r 'TOr£ Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA Methods of Increasing Hot Climates H, R. ITTNER T. E. BOND C R KELLY IMER RATIONS ZALIFORNIA AGRICULTURAL EXPERIMENT STATION BULLETIN 761 COMFORTABLE CATC Fifty-one per cent of the cattle in the United States, representing a cash value of 7% billion dollars, are in areas where the average summer temperature is above 75° F. Because many of these areas are close to important markets, have plentiful supplies of water and high quality feeds, cattlemen have for a long time been interested in ' improving their beef production in such hot areas, notably the des- erts of California. Experience and experiments have shown that beef production drops considerably in hot summers as cattle become uncomfortable and eat less. Since 1946 the Animal Husbandry and the Agricultural Engineer- 1 ing departments of the University of California in cooperation with the United States Department of Agriculture have been conducting experiments at the University experiment station in El Centro, Cali- fornia, to study the effect of different hot weather environments on beef cattle. The goal of the experimenters has been to devise means whereby cattlemen could make their beef animals more comfortable - during the hot months and carry out profitable year-round operations. The experiments have resulted in a number of practical applications which may be carried out by farmers at minimum expense. The steps to be taken to maintain animal comfort and production revolve I around five key factors . . . Shade . . . Water . . . Air Movement . . . Radiation . . . Feed. SHADE . . . Properly designed shades will reduce the radiation heat load on cattle up to 50 per cent. Most shades in the desert areas are from 16 to 20 feet wide and up to several hundred feet long. Experi- | ments indicate that 10 to 12 feet is the best height for a cattle shade. I £1.5 How roofing materials and coolers influenced average daily gain GALVANIZED IRON ALUMINUM AND WET BURLAP HAY OVER WET GALVANIZED IRON ENCLOSED SHADE WITH COOLER [2] OW BETTER DAILY GAINS IN WEIGHT Although east-west orientation is best from the standpoint of re- ducing radiation heat load, experimenters found that shades oriented north and south, so that the sun would cover the entire area for part of the day, improved sanitary conditions. The experimenters used galvanized steel sheets, aluminum sheets, boards and hay as roof material. Hay proved to be the coolest of all materials tested although it provides problems of replacement, pro- tection from wind and damage when wet by rain. Hay should be held together by two layers of wire net to reduce blowing. It was also found that by painting the top side of metal white, the radiant heat load under the shade could be reduced considerably. Painting the underside of a metal roof black also was found to be an aid in reducing radiant heat load on the animals because the dark paint absorbed radiation from the ground rather than reflecting it back onto the animals. Although tests were not conducted to ascertain the shade space requirement per head, it is believed 60 square feet per head is ade- quate. The important thing to remember is to avoid crowding during summer months. A complete summary of shade experiments may be found on page 32. WATER . . • Experiments were conducted to increase animal gains by using water to wet the cattle in pens and by cooling drinking water. The use of sprays, hoses and other methods of wetting animals was not too successful unless the animals were wetted to the skin. Investigators believe that the humidity increase occasioned by the use of water may slow the evaporation of moisture from the cattle, and in fact make it more difficult for them to retain thermal balance. 3.0 CO 2.5- CD 2.0 §1.5 1.0- How air movement, water temperature and corral construction influenced daily gains _ NATURAL AIR MOVEMENT MECHANI CAL LU is O y- C-3 O =££ 5= o ^ O I— si is i j- ^=c o ^ 5= — O en O cc [3] They do however feel that such programs may be of value in areas less humid than the location of the experiment station. The cooling of drinking water on the other hand did appreciably increase animal comfort and production. By keeping drinking water at about 65° F., noticeable gains were reported. While mechanical refrigeration costs are probably too high for commercial programs, other methods of cooling were suggested. Evaporative water towers helped keep water cool. By using underground pipes from wells where the water was already at a low temperature, experimenters were able to obtain cool water at little or no extra cost. By keeping water in shallow tanks so that cool water could not be reached by the cattle and by covering tanks except for small drinking holes low temperatures were maintained. Shaded drinking tanks also proved val- uable but shades should not be large enough to allow animals to stand under them. A complete summary of experiments with water is on page 50. AIR MOVEMENT . . . Increased air movement has proven to be of great benefit to cattle. Either mechanical or natural means can be utilized to increase the circulation of air in cattle pens. Without incurring extra expense cattlemen can take advantage of natural conditions to increase circulation by proper corral construc- tion. Wire or cable corrals offer little resistance to natural air move- ment and during tests resulted in significant gains compared to cattle penned in wooden corrals. Proper orientation of corrals to take advantage of air movement in the area is also important. The experimenters successfully employed large fans, operating either full or part time, to increase air movement over penned cattle. Even though penned in wooden corrals, cattle subjected to mechanical air movement made better gains than animals in wooden corrals without fans. Experimenters feel that the gains more than offset the cost of operating fans. Although cattle are not considered to be sweating animals, recent studies indicate that they may lose a large amount of moisture through the skin and that increased air movement speeds up evapora- tion of the moisture and brings about more rapid cooling. A complete summary of air movement experiments can be found on page 66. RADIATION . . . The sky, the ground, the corral, nearby buildings, literally everything in sight, radiates heat onto the cattle. Reducing this radiation is a complex but not insoluable problem. Corral construction, which plays an important role in promoting increased air circulation, is also important in controlling radiation. Wire or cable, because it offers relatively little area for absorbing or reflecting heat, has proven much better than wood for this purpose. The fences in a wooden corral absorb a great amount of heat and radiate it directly back onto the penned cattle. Buildings, hay stacks, large farm machines and other obstacles which would radiate heat should not be located near corrals. This will also permit free circulation of the air. If at all possible cattle pens should be located near growing crops. Cattle in pens in such surroundings showed much better gains than [4] animals subjected to radiation from the bare earth, roads or other surfaces. Air temperatures in the vicinity of growing crops were significantly lower. Experiments with special electronic equipment revealed that the north sky usually is cooler than the rest of the sky. The temperature of the sky was measured. Orientation of shades and fences so that animals can be exposed to this cool area of the sky is another factor in promoting animal comfort. A summary of radiation experiments can be found on page 75. FEED . . . The proper ration for hot weather is extremely important in beef production. Care should be taken not to supply high fibre diet during hot months. Such feeds produce a high "heat increment" which must be dissipated by the body, a difficult task in hot weather. In general, a summer ration should be good quality roughages and grains. In general, cattle in the desert with proper shade, corrals, water and diet can be expected to gain two pounds per day or more. However, experimenters found that it was advisable to bring cattle into the desert area before the mid-summer heat so the animals could become accustomed to the high temperatures of that period gradually. Best results were obtained if the animals were brought to top finish in the spring or fall, rather than in the heat of the summer. A complete summary of feeding experiments may be found on page 78. 150- How roofing material influenced temperature of various shade structures gioo CO JUNE 25 1:35 P.M. 50 en o o o a U_l CJ3 (2) AUGUST 19 11:10 A.M. AUGUST 22 12:00 NOON [5] CONTENTS Reasons for Study 7 High temperatures and production 9 Basic approach 10 Cattle Shades 18 Summary of shade tests 32 Water as a Cooling Agent 34 Summary of water tests 50 Air Movement and Temperature 52 Summary of air movement and temperature tests 66 Radiation 67 Summary of radiation tests 75 Rations for Summer Production 76 Summary of feeding tests 78 Costs and Power Consumption 78 Summer Water Requirements 80 THE AUTHORS: N. R. Ittner was Specialist in Animal Husbandry, Imperial Valley Field Station, El Centro (deceased). T. E. Bond is Agricultural Engineer, USDA, Davis. C. F. Kelly is Professor of Agricultural Engineering and Agricultural Engineer in the Experiment Station, Davis. APRIL 1 958 METHODS OF INCREASING BEEF PRODUCTION in HOT CLIMATES* N. R. ITTNER T. E. BOND C. F. KELLY Introduction Why, how, and when the studies described here were conducted Reasons for Study The heat load on animals is high dur- ing the summer in the Imperial Valley, Coachella Valley, Palo Verde Valley, and other desert areas of California. Environmental studies to determine ways and means of making livestock more comfortable during the hot weather have been in progress at the University of California's Imperial Valley Field Sta- tion since 1946. Heat in this area is generally of the dry type although there are about six weeks every summer when a humid con- dition develops from moist air blowing in from the Gulf of California. The adverse effects of a hot environ- ment on livestock are more pronounced than those of a cold environment. Vari- ous studies have shown the effect of heat on livestock, with dairy cattle at the University of Missouri (Ragsdale, Brody, et al., 1948) and California (Re- gan and Richardson, 1938), with swine at the University of California (Heitman and Hughes, 1949), with poultry at the Beltsville (U.S.D.A.) Research Center (Ota, Garver, and Ashby, 1953), and with beef cattle at the Imperial Valley Field Station (Ittner and Kelly, 1951). All of these investigations have shown that the depressive effects of heat begin to be felt at a relatively low temperature level, around 75° F.f This is known as the critical temperature and can be de- fined as the air temperature beyond which cattle begin to have a higher than normal body temperature. ^ There are many areas in the world where high temperatures are a problem in livestock production. Here in the United States the 75° isotherm (fig. 1) divides the country into two parts: All of the area south of the line has an average temperature above 75° during July, which is the hottest month in all parts of the country, except along the Pacific Coast, where August is hotter. The region south of the isotherm con- tains 51 per cent of all the beef cattle and calves and dairy cattle (including * Submitted for publication April, 1957. f All temperatures in this bulletin are on the Fahrenheit scale. [7] heifers over two years old) of this coun- try (U.S.D.A. Agriculture Statistics, 1953). Their 1953 value in farm and ranch was over 7Vs billion dollars, out of a total for the country of 16% billion dollars. In many parts of the world, work is in progress to develop more productive animals that are adaptable to their par- ticular hot climated In the southern part of the United States much of this work is being done with Brahmans or Brah- mans crossed with the exotic breeds and with the Charolais cattle of France. The King Ranch in Texas has developed the Santa Gertrudis breed by crossing the Brahman and Shorthorn (Rhoad, 1955) . In our country we usually think of the Brahman as the only heat-tolerant ani- mal, but there are a number of other areas that have heat-tolerant, indigenous types of cattle, such as the Boran cattle of Kenya, the N'dama in French Guinea, or the Criollo cattle of Venezuela. Con- siderable improvement can be, and has been made through selection, but this method has its limitations and progress is slow. New improved types can be de- veloped faster by crossing these indige- nous types with one of the more produc- tive breeds. South Africa is using the Africander with the Hereford and Short- horn to get a more desirable beef type adaptable to their conditions. Much pro- gress is being made along these lines, but all are long-range programs which no doubt will eventually provide the hot regions of the world with more produc- tive types of animals. ' A more immediate approach to this problem was needed for our desert areas since more and more cattlemen are oper- ating on a year-round basis. The envi- ronment project described herein was Fig. 1. 75° F isotherm for average July air temperature in the United States, and number and value of livestock in areas north and south of isotherm (U.S.D.A., Agric. Statistics). (Isotherm from Climate and Man, U.S.D.A. Yearbook, 1941.) [8] established to find ways of reducing the heat load on animals, and the results of the last ten summers' experiments are discussed in this bulletin. Some of the methods tested have proved to be very helpful, while others have not proved to be too practical.\The results of these experiments will be discussed and illus- trated and methods of application to a livestock program will be recommended. Many of the methods are also applicable to heat-tolerant animals since they per- form better under less rigorous condi- tions^ Nearly all of the tests were made with Hereford cattle since they seem to be the most heat-tolerant of the European breeds and are the popular breed in the west. Effect of High Temperatures on Production Heat tolerance is the term applied to the animal's ability to escape the adverse consequences of a hot environment. Just what constitutes heat tolerance in an ani- mal is not definitely known, but all the evidence points to the fact that it is a complex entity. It is known that tropical cattle have a higher heat tolerance than temperate-zone cattle, and among the European cattle some breeds have more heat tolerance than others. Body tem- perature is one way of checking heat tolerance (Rhoad, 1944). Bonsma (Bonsma and Pretorius, 1943) in South Africa has done a great deal of work with cattle in tropical environments and has shown that short-haired cattle have a lower body temperature and grow faster than those with woolly coats. He has also shown that light-colored cattle reflect more solar heat than those with dark hair. An animal's suitability to an en- vironment is indicated by heat tolerance, growth, feed efficiency, high fertility, and low incidence of disease. The indigenous cattle found in the semi-arid subtropics are usually rather large-framed animals like the Africander. In the humid tropics heat dissipation is most difficult so an animal with a large skin area per unit weight is desirable. These characteristics are found in the small Nguni breed of South Africa. Many livestock men and scientists throughout the world have noted that when European breeds of cattle are moved away from the cool climatic con- ditions of their native home and placed in a hot environment they show marked distress and low productivity. Some of this distress and low productivity is un- doubtedly due to the plane of nutrition, the parasitic condition of the animals, and management practices, all of which, more often than not, are quite different from what they have been accustomed to. Internal and external parasites are usu- ally more severe in a hot, humid climate than in a hot, dry climate. California's desert areas are hot and dry most of the year, and the parasitic problems are not serious. Anaplasmosis is one para- site that has been a problem from time to time. With the increasing numbers of animals, parasites are likely to become more of a problem. However, it should be remembered that sanitation is the answer to many disease problems and good hot sunlight is one of our best dis- infectants. Except for the summer heat, this re- gion is an ideal place to feed cattle. There is an abundance of feed, such as alfalfa, sudan, barley, and milo. There is also plenty of cheap irrigation water and very little rain to create a mud prob- lem for the cattle. Last but far from least, is the region's proximity to the growing Los Angeles market. Heat in this area is severe enough to materially reduce the daily gain of beef cattle, and dairy cattle have more than a normal drop in milk production. When the body temperature rises, usually at air temperatures of 75°-80° F for Eu- ropean and 95° F for Indian cattle, the animals lose appetite and reduce feed intake; this reduces their metabolic rate and keeps them cooler, but it also re- [9] duces daily gain and milk production (Worstell and Brody, 1953). Cattle in this region show little loss of production with daytime temperatures of 110° to 115° F if the night tempera- ture drops to around 60° F. When the maximum temperature is 105° F and the minimum is 80° F for two or three days, there is an immediate drop in food con- sumption and reduction in daily gain. Most of the environmental studies re- ported herein have used summer gains and feed efficiency of beef cattle as in- dices for testing different feeds and man- agement practices. Cartwright (1955) reports that summer gains are sufficiently high in heritability (19 per cent) to be useful in selecting breeding animals. Although considerable information has been gathered throughout the world on the reactions of cattle to thermal stress, there is still a great deal that is not known concerning the fundamental physiology of temperature regulation in cattle, as well as the anatomical differ- ences responsible for their adaptability to heat. A Basic Approach to the Problem An animal is continually producing heat from the feed it consumes. Since only a part of this feed energy is utilized in the production of milk, meat, and fat, and for body maintenance, the excess must be disposed of. For an animal to be thermally comfortable there must exist a balance between the energy added to it and that utilized by, or removed from it. The problem of keeping live- stock cool during hot weather is essen- tially one of aiding the animal to main- tain a proper energy balance. It is quite possible to control or modify most of the factors affecting this balance. To under- stand better how this may be accom- plished and to form a basic approach to the problem, it is essential to consider the four modes by which heat, or energy, is transferred between an animal and its environment. Convection: By convection an animal can lose heat to, or gain heat from, air circulating around it, depending on whether this air is cooler or warmer than the animal surface. The amount of heat exchanged is controlled according to the relationship: Q c = CAV n (t 1 -t 2 ) Here Q c is the convective exchange of heat, V is the air velocity, A is the animal surface area, (t x - t 2 ) is the temperature difference between air and animal sur- face, and C is the convection constant. The amount of heat exchanged varies linearly with animal surface area and with the temperature difference between animal surface and air. It varies non- linearly with air velocity (wind). The value of the coefficient C is dependent upon the characteristics of the surface (in the case of cattle the length and thickness of hair, how much hair, and whether curly or straight). The value C also depends upon the direction of air flow with respect to the surface. Evaporation: For each pound of mois- ture evaporated, about 1050 Btu of heat are exchanged. The rate of energy ex- changed between the surrounding air and an animal's surface can be described by an equation of the type, Q e = KAV n A(p s -p) Here Q e is the evaporative heat ex- change, V is the air velocity, A is the animal surface area, A is the latent heat of vaporization of water, (p s - p) is the difference in partial pressure of the water vapor at the animal surface and in the surrounding air, and K is the evaporative constant, which, like the convective co- efficient is affected by the type of surface and its directional relationship to the flow of air. The air velocity exponent, n, is similar to that in the convection equa- tion above which means that evaporative [10] and convective exchanges of heat are similarly affected by wind. In the case of beef cattle, as with most livestock, mois- ture is also removed from the respiratory areas, and the amount of heat exchanged by this method is greatly affected by the rate and extent of respiratory activity. Radiation: All surfaces radiate, ab- sorb, and reflect energy (heat) in amounts dependent upon the tempera- ture and character of the surface. Any two surfaces, then, are continually ex- changing heat at a rate defined by the equation, Q r = AaF a F e (T 1 4 -'iY) Here Q r is the radiation heat exchange, A is the area of one surface, a is the Stefan-Boltzman constant, F a is a factor that allows for the relationship of one surface to another (sometimes called "shape" or "seeing" factor), and T 1 and T 2 are the absolute temperatures of the two surfaces. The factor F e allows for the radiation characteristics, emissivity* and absorptivityt, of the two surfaces. Conduction: Heat is transferred by conduction through an object if there is a temperature gradient present, or from a warm surface in contact with a cooler surface, at a rate determined by the equation, Q k = UA(t 1 -t 1 ) Here Q k is the conductive heat trans- ferred, A is the area through which heat is transferred, (t x - t 2 ) is the tempera- ture gradient through the object or be- tween two surfaces, and U is the over-all heat transfer coefficient of the system. * Emissivity: the ratio of the intensity of radiation of any given wavelength emitted from unit area of a surface to the intensity in the same wavelength from unit area of a black body at the same temperature. t Absorptivity : the fraction of incident radi- ation absorbed by a substance. At any wave- length and temperature the absorptivity of an opaque substance is equal to its emissivity or to one minus its reflectivity. Conduction is perhaps the least impor- tant of the four modes by which heat is exchanged externally by an animal. There is also some exchange of heat with surrounding air by conduction. Treatment of these four modes of heat exchange has been highly simplified for sake of illustration. Also, they have been treated as being independent. For in- animate objects independent treatment is often possible — for an animal it is not. For example, environmental temperature affects the surface temperature of ani- mals so that any change in environ- mental temperature is accompanied by a change in surface temperature. The equations given above show that each mode of heat exchange is affected by the respective levels of these two tempera- tures (in the evaporation equation the vapor pressure is a function of tempera- ture). All other factors affecting heat exchange are equally interdependent so that approaching the problem of cooling livestock solely on a theoretical basis is highly illogical. The other approach is experimental. The four equations point out all the factors affecting thermal comfort of ani- mals. Since any improvement of the thermal comfort of an animal must be made through some modification or con- trol of these factors, these are listed be- low and they define what areas can and should be investigated to provide ther- mal relief for animals in a hot environ- ment. This was the approach that guided the research reported in this bulletin. A. Air Temperature Humidity Velocity Direction B. Animal Surface temperature Surface area Surface characteristics Surface evaporation Breed Feed Water [11] C. Surroundings Temperature of surrounding surfaces Radiation characteristics of surrounding surfaces Location with respect to animals Solar and sky radiation Cooperative Nature of Study Cooperative programs in research are imperative if scientific information is to continue to expand. This study has three cooperators, the Animal Hus- bandry Department and the Agriculture Engineering Department of the Univer- sity of California and the United States Department of Agriculture. All three have contributed men, money, and mate- rials for the development of this program. Since these experiments are primarily a study of the heat exchange between the animal and its environment, many engi- neering instruments have had to be used in order to measure heat flow both to and from the animal. Evidence is beginning to accumulate that the gaining ability of cattle in a hot environment is directly re- lated to its comfort and heat tolerance. The Climate Factors that make beef raising difficult in the desert area Air Temperature, Wind Velocity and Relative Humidity Two terms used for the classification of summer weather are "hot dry" and "warm humid." These two conditions occur in nature, but quite often any one place will have variations or combina- tions of these two types of weather dur- ing the summer. Death Valley in Cali- fornia is an example of a hot, dry area, while the states bordering on the Gulf of Mexico have warm, humid summers. A hot, dry environment is character- ized by high air temperatures, low hu- midity, and dry ground with little or no vegetation. Such conditions provide very few clouds or moisture vapor in the air to remove the intense rays of the sun. These high temperatures and direct solar radiation are bad, but there is also the intense reflection of the sun's radiation from the dry ground. However, there are two factors operating here which prevent these conditions from becoming unbear- able: one is the dry air which facilitates evaporation of water, and the other is the clear sky which allows considerable heat from the ground to radiate into the upper stratosphere. Warm, humid climates are character- ized by clouds and moist air, which re- move some of the solar radiation, and vegetative cover which reduces the radia- tion heat load from the ground. Air temperatures in these climates are mod- erate and seldom above the animal's skin temperatures, but the evaporation of wa- ter is very slow. Most people find the wet, sticky condition of the skin distinctly uncomfortable in these regions. Increas- ing air movement in a humid area aids in the evaporation of water and makes life more comfortable to human beings. High winds with high temperature and a low humidity can be most uncomfortable because of their drying effect on the body. Imperial Valley, Coachella Valley, and Palo Verde Valley are, in many respects, typical of a hot, dry region, but for about six weeks every summer these valleys become hot and humid. This phenom- enon is brought about by a prevailing wind from the south, bringing moisture [12] from the Gulf of California. During the remainder of the year the prevailing wind is from the west. This six-week period also has a number of tropical thunder showers, usually local and at times quite destructive. Relative humid- ity readings are usually below 40 per cent during the heat of the day and more often than not range betwen 15 and 35 per cent. When the noon humidity is 30 per cent or above, human beings become uncomfortable. Fortunately, excessively high temperatures do not usually prevail during this humid period; maximum temperatures range between 100° and 105° F. However, minimum tempera- tures become excessive, seldom dropping below 70° F. Furthermore, they are sel- dom below 80° F for more than four hoursiyThe moisture-laden air from the Gulf radiates the heat back to the earth instead of letting it dissipate in the upper atmosphere. Since the ground cannot cool, night temperatures rise and the mean temperature for the 24-hour period goes well above the critical temperature for cattle (75-80° F) with a consequent drop in production. XThere are periods when the night temperature does not drop below 80° F for 15 to 20 days at a time. These desert areas have a mean monthly temperature above 75° F for about six months of the year ; for nearly four months it exceeds 85° F and for two months it is 90° F. Figure 2 shows the temperature and humidity for a typical hot, dry day and a hot, humid day for the Imperial Valley. Air movement during the summer is negligible, although for an hour or so winds may reach velocities of 40 to 50 miles per hour. The average wind vel- ocity during the summer is around 2.5 miles per hour 3 feet above the ground. With very little air movement, high tem- perature, high humidity, and very few clouds, a few days each year are almost unbearable. Environmental studies reported herein were conducted each summer between June 21 and September 27. Weather records were kept every summer, and table 1 shows the average maximum, minimum, and mean air temperatures and relative humidities for the test pe- riod of 1947 to 1956 inclusive. Although the Imperial Valley and sur- rounding areas have a humid condition during part of the summer, the humidity is still lower than that of the states around the Gulf of Mexico. Figure 3 shows average diurnal air temperatures and relative humidity at the Imperial Valley Field Station, California, Baton Rouge, Louisiana, and Corpus Christi, Texas, from July 6 to September 14, 1955. Air temperatures at the Field Sta- tion averaged 102° F during the heat of the day, while the relative humidity was 20 per cent. At Corpus Christi and Baton Rouge air temperatures average around 87° F and relative humidity about 60 per cent during the middle of the day. 115 Hot dry day Aug. 3, 1955 Hot humid day Aug. 9,1955 90 Fig. 2. Diurnal air temperature and relative humidity for a hot, dry day and a hot, humid day at the Imperial Valley Field Station. [13] Table 1 — Weather During Feeding Periods Data for Imperial Valley Field Station During Test Periods, 1947 to 1956 Inclusive Year Period of feeding trial Air temperature (F.) Air relative humidity (%) Ave. Max. Ave. Min. Mean Ave. Max. Ave. Min. Noon Mean* 1947 July 23 to September 15 . . . 105.7 74.7 90.2 67 26 34 46 1948 July 28 to September 20 . . . 108.1 74.7 91.4 55 17 25 33 1949 July 12 to September 16 . . . 104.3 73.4 88.9 71 24 31 44 1950f June 21 to September 9 105.1 74.8 89.9 76 28 39 47 1951 July 3 to September 27 ... . 103.7 71.8 87.7 78 29 36 50 1952 July 2 to September 11 ... . 106.7 77.7 91.8 66 26 26 40 1953 June 30 to September 22 . . . 105.5 77.1 91.3 61 19 24 36 1954 June 24 to September 16 . . . 103.6 76.4 90.0 67 19 28 39 1955 July 6 to September 14 ... . 103.2 78.3 90.3 80 23 29 46 1956 June 27 to September 5. . . 102.4 74.2 88.3 68 17 22 36 * The mean relative humidity is the average of all 2-hr. readings throughout the period. t One group was fed from June 14-September 5 and weather data are almost the same as those shown. Tallahassee, Florida, is about the same as Baton Rouge, Louisiana; but the data are not included in figure 3. As a further comparison of the difference between a "hot dry" and a "warm humid" climate, figure 4 shows the mean daily air tem- perature for the Imperial Valley Field Station, California, Corpus Christi, Texas, Baton Rouge, Louisiana, and Tal- lahassee, Florida. Mean daily air tem- peratures are about 90° F for the Cali- fornia Station and between 80° and 85° F for the other three stations. Rainfall during June, July, August, and September is rather heavy in the Gulf Coast States, averaging 11 inches for Corpus Christi, 20 inches for Baton Rouge, 26 inches for Tallahassee, and only 0.7 inch for El Centro. Air move- ment in these Gulf Coast States varies some, but the average ranges between 5 and 12 mph, while in the Imperial Val- ley it averages around 2.5 mph for the summer months. Air movement at the station was taken 3 feet above the ground. Climatic conditions are different in these four areas, but all have somewhat similar problems in livestock production because of their summer heat. Solar and Sky Radiation As will be discussed later (page 18), a large part of the heat load on an animal is due to radiation from its surround. The solar and sky radiation influences, directly or indirectly, the thermal en- vironment of entire areas and is depend- ent, at any particular time, upon altitude, latitude, cloud cover, and air moisture, gas, and dust content. The United States Weather Bureau has for many years used Eppley pyrhelio- meters to observe solar and diffuse sky radiation throughout the country. These measurements indicate a higher than av- erage radiation intensity in the Imperial Valley as compared with other sections of the country at the same latitude. For instance, the July, 1955, isolines for this area show a daily average solar radiation of about 600 langleys, whereas the south- eastern part of the United States aver- aged about 500 langleys. Much of this difference can be attri- buted to the greater cloud cover in the [14] 105 100 >/^^ ^^N 95 Temperature \ • ...<** / - / \ / ..-•*■'" \ / u_ \ J \V ...•** Relative ^ 90 V / \ / jf /\ ,^ p * humidity — UJ cr < h- 85 ^ < a: UJ a. 2 80 s\/ /An / Temperature ,> N ..' *••.. ^s. jt V.o «''. ** \ - -.^ V^ >»^ _ ••. 6 s > I I 1 I M 5 IOI5 2025305 10 15 2025 31 5 10 15 2025 31 5 10 15 202530 JUNE JULY AUGUST SEPTEMBER [15] described on page 17 indicate many days during July and August with noon half- space radiation intensities on a horizon- tal surface of 425 to 475 Btu/hr. sq. ft. as measured by a total energy radiometer and of about 300 Btu/hr. sq. ft. as meas- ured by an Eppley pyhrheliometer. Experimental procedures and instruments The results of a good many feeding trials are reported in this bulletin, and to eliminate repetition the standards used are discussed in this section. All animal weights, unless otherwise noted, are after a 10-hour stand in a dry corral without feed or water. In most cases weights were taken every 28 days. The wooden corral pens were 50 x 50 feet enclosed by a 6-foot fence construc- ted of four 2 x 10-inch planks. Each pen had a hay or aluminum shade 10 feet above ground. All wire pens were made of ordinary fence wire and all have hay- covered shades at least 10 feet high. Water consumption was measured by calibrated water meters on the water in- lets. Since the accuracy of these meters is highest when a full stream of water is flowing through them, a float and micro- Fig. 5. Portable "spot" climate recorder. The 4-pen clock-operated recorder provides 24-hour records of air and ground temperatures, globe- thermometer temperature, and wind velocity. switch were arranged with a solenoid water valve so that full flow was obtained whenever the water level in the tank dropped 1 inch. The water meters were read at least once a day; and on some days hourly observations were made. Pen recorders kept a continuous record of the temperature of the water near the top of the tanks. Not all lots had these record- ers. Feeding was by hand and all lots were fed twice a day. The instruments used for defining the environment were for the most part port- able, so that they could be moved from pen to pen, or from pen to open area. A continuous record of air temperature and relative humidity was, however, obtained by a Friez hygrothermograph located in a standard Weather Bureau shelter about 600 feet from the main corrals. In recent years some wind-velocity data have also been collected at this location. The Friez cup-type anemometer used for measuring wind velocity was only 3 feet above the ground, a little more than half the height of a standing cow. As new instruments became available they were used in the project, so that the same types of instru- ments were not necessarily used through- out the period covered by this report. The portable instruments were of two general types: those for measuring the air temperature and velocity, and those for measuring radiation. Air temperature and velocity: Small portable weather stations were used where a continuous record of air temperature and velocity was required at a particular location over periods of sev- eral weeks or months. These have been described in detail by Schultz and Brooks (1956). A 4-pen clock-operated recorder allowed 24-hour or 7-day rec- ords to be obtained. One pen recorded air temperature as sensed by a fluid-filled capillary tube, another ground tempera- ture, and a third globe-thermometer tem- perature. The latter was 8 inches in diameter. The fourth pen was used to record impulses from a Friez cup-type [16] anemometer, at the rate of one impulse for each 1/12 mile. A view of one of the portable or "spot" climate recorders is shown in figure 5. Other devices used to measure air temperature were small copper-constan- tan thermocouples shielded with metal cylinders, mercury thermometers, etc. The Alnor Velometer, a vane-type ane- mometer, was also used to indicate air velocities. Radiation: Since such a large part of the experiment was related to protecting the animals from solar radiation, special attention was given to radiation measur- ing instruments. To measure total spheri- cal radiation (both sky and ground), globe thermometers — either 6 or 8 inches in diameter — were used. These give, by means of the internal temperature of a black, hollow copper sphere, the result of the combined effects of air tempera- ture, spherical radiation, and air veloc- ity. By calculation, the mean radiant temperature of the entire surround may then be obtained with varying accuracy, depending upon the rates at which the climatic factors — air temperature, radia- tion, and air velocity — are changing. A complete discussion of this instrument has been given by Bond and Kelly (1955). Recently the "spherical radiometer" was developed for this project and has been used especially for checking the mean radiant temperatures as measured by globe thermometers. This instrument consists of two 2-inch-diameter spheres, one of polished silver, the other black. The spheres contain heating elements by which the sphere temperatures can be maintained equal and convection losses compensated for. The current used is a measure of the spherical radiation (Dun- kle and Gier, 1954). To measure half-space radiation, or the energy falling on a flat horizontal surface, use was made of the total energy plate radiometers developed by the Il- lumination Laboratory, University of California, Berkeley. (See Gier and Dun- kle, 1951, for complete description) . The sensing element of this instrument is a thermopile, whose electromotive force was indicated by a Leeds and Northrup No. 8662 semi-precision potentiometer in field observations, and by a Brown re- cording electronic potentiometer in sta- tionary use. A view of the instrument on its tripod in the field is shown in figure 6. This instrument is designed to meas- ure all radiant energy falling upon a horizontal surface, including both long and short wave-lengths. There is no cover of glass or other material to act as a fil- ter, and the receiving surface has a high absorptivity for all wave-lengths. Another instrument sometimes used to measure half-space radiation was the Eppley pyrheliometer, described by Lee (1953). Because its sensing element is covered with glass, it measures only the solar and diffuse energy, and screens out most of the long-wave atmospheric ra- diation. The "Solarimeter" as developed by Gier and Dunkle was used at times for measuring half-space radiation (solar and diffuse), its response being similar to the Eppley pyrheliometer. It consists Fig. 6. Flat-plate radiometer and solarimeter mounted for portable field use. [17] of two thermopiles encased in a plastic cover, one painted white, the other black (figure 6). Brooks (1951) has stated that the solar and diffuse radiation amounts to about 60 per cent of the total sky radia- tion as measured by the total energy radiometer. Since an animal's surface absorbs both short and long-wave en- ergy, it seems that the total energy radi- ometer would Be a better indicator of radiation heat load upon an animal than would an instrument of the type of the Eppley pyrheliometer. Where it was desired to determine the radiosity of a smaller area or object, one of two instruments was used — either a Gier directional radiometer or a Hardy dermal radiometer. These have been de- scribed in detail by Kelly, Bond, and Lorenzen (1949) and by Hardy (1934). The sensing elements of both instru- ments are blackened thermopiles. The Gier radiometer has a cone opening of 16°, the Hardy dermal radiometer one of 12°. They were used to obtain radi- osity and temperature of cattle surfaces, shade and corral materials, ground cover, and effective sky temperatures in selected locations. The Experiments Studies of different materials and techniques for cooling animals Providing a comfortable environment for livestock during the hot summer can be considered as a problem in heat trans- fer. There are four avenues of heat trans- fer available to the animal for cooling itself: Radiation, convection, evapora- tion, and conduction. These four meth- ods do not operate alone, and their ef- fects on cattle are always changing. To study one of these methods of heat trans- fer by itself is impossible, since cattle in the open are also affected by the other three means of heat transfer at the same time. Since all four methods are operat- ing together most of the time, this study has been broken down into five cate- gories: cattle shades, water as a cooling agent, air movement, radiation of an ani- mal's surrounding, and rations for high summer temperatures. CATTLE SHADES Shades will reduce the radiation heat load from the sun and sky by more than 50 per cent. There are a number of fac- tors that cause the effectiveness of any given shade to vary. For a more detailed discussion of these factors and their ef- fect on thermal design of shades see Kelly, Bond, and Ittner (1950). An animal in the sun receives radiant energy from three sources: (a) sun and sky, (b) unshaded ground, and (c) hori- zon, actually a. band extending about 10 degrees above the horizon which is sep- arated from the remainder of the hemis- phere in calculations because it radiates at a greater rate as a result of back radi- ation from moisture in the heated air near the ground. On a typical August day at the Im- perial Valley Field Station the total ra- diant heat load on an animal in the sun was 244 Btu per hour ft. 2 (of animal surface), as determined from black- globe thermometer readings. Under a shade the radiant heat load was 167 Btu per hour ft. 2 Shade reduces radiant heat load from the sun and sky, and substi- tutes shaded area for part of the hot [18] ground, but it adds a new source of en- ergy, the shade material itself. In this instance the total effect was nevertheless a reduction of the radiant heat load on the animal, from 244 to 167 Btu per hour ft. 2 of animal surface. This is equivalent to reducing the mean radiant temper a- i ture* of the animal's surround from 153° to 98° F. Shade Material Several different types of shade ma- terial and two heights of shade — 7 feet and 12 feet — were tested during the sum- mers of 1947, 1948, and 1949. In 1947 the weighing facilities and the number of animals involved in the tests were in- adequate, but a considerable number of radiation readings were taken through- out the summer. Four shades were tested during the summer of 1947; each was 16 x 24 feet and 10 feet high at the eaves. The roofs are gable with about an 18- inch rise. A brief description of each follows: I.Wood slat shade. The roof is constructed of 1 x 10 inch boards spaced 1 inch apart. The cracks run east and west. The floor is dirt. 2. Hay covered shade. The roof is about a 6-inch layer of coarse hay held in place between two layers of woven- wire fencing. The floor under the shade is concrete. 3. Aluminum shade. The roof is commercial 5-V Crimp aluminum sheets. The floor is concrete and has a 2-inch drain in one corner. Overhead, down the center of the shade, are several spray heads which may be used to produce a fine spray under the shade. Although this shade was equipped with the sprink- lers, it was tested without the sprinklers with the radiation instruments. * Mean radiant temperature: that tempera- ture of a uniform enclosure (usually designated black to eliminate reflection) with which a body would exchange the same amount of energy by radiation as in the actual environ- ment. 4. Galvanized iron shade. The roof is old, corroded corrugated galvanized sheet iron, and the floor is dirt. In June, 1947, before animals were available for the experiment, the inten- sity of radiation under each shade was compared with that from the unshaded sky and sun by means of a flat-plate radi- ometer. The instrument was held 3 feet above the ground, and readings were made on both the upper and lower hemis- pheres. The observations covered a pe- riod of several hours during the hottest part of the day. When measuring the radiation under a shade, the instrument was held at the center of the shadow. From 10 A.M. to 2 p.m. the radiation from the upper hemisphere was reduced 65 per cent by the solid shades (galvan- ized iron, aluminum, and hay covered), and 55 per cent by the wood-slat shade. This agrees well with the findings of workers in Africa (Reinerschmid, 1943) . There was a slight difference in the amount of energy reaching the flat-plate under the various shades. For instance, at 12 noon, when the air temperature was 99° F, the energy incident on the instrument under the hay shade was 181 Btu per hour/ft. 2 ; under the aluminum shade, 190; under the galvanized shade 193; and under the wood slat shade, 223. At this time the total solar and sky radi- ation, including incoming long-wave at- mosphere radiation, amounted to 527 Btu per hour/ft. 2 . In other words, the hay covered shade cut off 1.7 per cent more of the solar energy than did the aluminum shade, 2.3 per cent more than the galvanized iron, and 8 per cent more than the wood slat shade. It was found that shades also reduced the radiation from the lower hemisphere, or the ground, although not as much. At 12 noon, when the ground radiation in the sun, amounted to 242 Btu per hour/ ft. 2 , the ground radiation under the solid shades averaged about 173 Btu per hour/ ft. 2 , a reduction of 28 per cent. Again there was a slight difference noted in [19 effect of the various shades. The hay and aluminum shades reduced the ground radiation 28 per cent, the galvanized iron 27 per cent, and the wood-slat shade 22 per cent. It should be noted that the sprays were not in operation under the aluminum shade at the time of these ob- servations, and that the ground or floor under all shades was dry. Some of the differences in ground radiation, how- ever, may be attributed to differences in floor material. In August quantitative measurements of radiation from the zenith and from several angles below the zenith, as well as from several angles in the lower hem- isphere, were made with a Hardy dermal radiometer. This instrument included in its view an angle of only 12°, rather than the entire hemisphere, as did the flat- plate radiometer. The results of the "scanning" of the hemispheres are shown in figure 7 for each of the shades. As with the flat-plate radiometer, the in- strument was held about 3 feet above the ground, at the center of the shadow. Galvanized Iron Spaced Boards -Hay Aluminum Fig. 7. Radiation from shade, unshaded sky, and ground at center of shadow, at noon, under four shades at the Imperial Valley Field Station. Observations made August 22, 1947. [20] Fig. 8. View of the hay-covered shade (left) and the slatted-wood shade (right). The air temperature was 95° F. The sprays under the aluminum shade were cut off, but the concrete floor was wet. As shown by figure 7, this instrument indicated a slightly different order of efficiency of the several shades in cutting off the solar radiation, namely, (a) aluminum, (b) hay, (c) wood slat, and (d) galvanized iron. The heifers under the hay-covered shade and wood-slat shade are shown in figure 8. While the animal standing in the shadow of a shade is protected from the direct rays of the sun, it is still receiv- ing and giving energy to and from the surroundings, depending on its surface temperature and emissivity, and the temperature and emissivity of the sur- roundings. The roof of the shade is usu- ally above the air temperature, during the daytime. Observations in August, 1947, indicated that at midday, at times when the air temperature was about 100° F, the temperature of the under- side of the El Centro shades (the side radiating to the animals standing in its shadow) averaged for the galvanized iron, 26° above air temperature; for the aluminum shade, 10°; for the wood shade, 9°; and for the hay shade, 5°. The original data are given in table 2 along with the emissive power as ob- tained by the Hardy radiometer. The value of each shade material in cutting off solar and sky radiation was also determined by the reactions of cattle sheltered under them. Between July 23 and September 15, 1947, three Hereford heifers were placed in the pens surround- ing each of the four experimental shades, and their physiological reactions, feed consumption, and weight gains were ob- served. They were fed fair quality al- falfa hay, a little cottonseed meal, salt, and water. Although the length of time was short, the number of animals small, and most differences between pens not statistically significant, almost all differ- ences followed the same pattern; that is, those animals under the hay and alumi- num shades appeared cooler and more comfortable than those under the wood- slat and galvanized iron shades. The normal body temperature of a cow is between 101° and 102°, while the com- fort zone for respiration rate is between 20 and 50 breaths per minute. Between July 23 and September 3, with a mean air temperature of about 90° F, 31 sets of body temperatures were taken on these [21] heifers. Unfortunately, there was a wild heifer under the galvanized iron shade, and only a few body temperatures were taken on this group. Body temperature averages were as follows: hay roof, 103.0° F; aluminum roof, 103.3° F; and wood slat roof, 103.5° F. The difference in respiration rates of the four pens was negligible, all averaging about 90 per minute. The average rate of gain for all ani- mals was poor, being 0.48 pound per day for the 55-day test period, but the ani- mals under the hay and aluminum shades again did a little better than those under the other two shades. Feed consumption followed the same pattern as the rates of gain. Salt consumption was normal. Cooling Shade Surfaces by Evaporation Animals may lose heat by radiation to the surround, as well as to the air by convection and evaporation, when the radiosity of the surroundings is less than that of the animal's surface. In 1948, water was used to cool the surface of two shades in order to lower their temperature (by evaporation), which thereby lowered that portion of the ra- diant temperature of the surround. Both shades had double roofs, spaced about 3 feet apart. In the first shade, a sub- roof of burlap sacks was kept wet by four sprinklers spaced evenly above it. Surplus water dripped from the burlap to a drained concrete floor, usually wet- ting the cattle somewhat in the process. The burlap sub-roof (21 x 21 ft. in size, compared with 16 x 24 ft. for the upper aluminum roof) was 7 feet above the pavement (fig. 9). The second shade had a water-cooled sub-roof of galvanized iron (16 x 24 ft.) , sloping to one side to carry surplus water to a drain, leaving the floor dry. The upper roof was of hay and of the same size. The plain galvanized iron shade mentioned previously was used as a check for these two cooled shades. In August, 1948, comparisons were made on the basis of (a) air temperature beneath the shades, (b) temperature of roof surfaces next to the cattle, (c) tem- perature of ground beneath the shades, and (d) amount of solar, sky, and ground radiation cut off by the shades. The average figures from a series of readings on a typical day, which had a maximum air temperature of 109° F, Table 2 — Temperature and emissive power of under surfaces of shades covered with hay, wood, galvanized iron, and aluminum, at Imperial Valley Field Station Date (1947) Time Mr temp., deg. F. Hay covered Wood covered Galv. iron covered Aluminum covered Temp., deg. F. E* Temp., deg. F. E* Temp., deg. F. E* Temp., deg. F. E* June 25 Aug. 19 Aug. 22 1:35 p.m.. . 100 98 102 108 95 101 104 107 114 101 174 160 167 104 106 112 115 110 190 181 174 122 120 139 125 128 194 180 187 112 127 124 118 172 166 156 2:30p.m ll:10a.m 2:40p.m 12:00 noon * Emissive power (Btu/hr/sq. ft.) as determined by Hardy radiometer. NOTE: Air temperature obtained by No. 30 BS gage shielded copper constantan thermocouple and surface temperatures by touch thermocouple of same size wire. [22] Table 3 — Average environmental conditions under the three shades on August 6, 1 948. Between 1 1 :00 A.M. and 1 :00 P.M. Comparison Galvanized iron check shade Burlap roof cooled by sprinklers Galvanized iron cooled by sprinklers Average outside air temperature (°F.) 103.5 104.0 127.5 107.5 56 27 103.5 101.5 89.0 97.2 61 37 103.5 101.5 92.0 100.0 62 31 Air temperature under shade (°F.) Temperature of underside of roof (°F.) Temperature of ground in shadow (°F.) . . Radiation from sun and sky cut off by shade (%) Lowering of ground radiation by shade (%) . . . . are given in and a minimum of 84° F, table 3. The temperatures of the undersides of the roof surfaces were markedly differ- ent. The wet, shielded, galvanized iron shade at times was 36° cooler, and the wet burlap was 45° cooler than the un- cooled galvanized iron roof. Cooling the sub-roof had little effect upon air tem- perature. Beneath both cooled shades the air averaged about 2° cooler than out- side. The check shade showed no lower- ing of air temperature. The wet pavement beneath the burlap- covered shade was as much as 10° lower than the ground below the check shade. The ground beneath the cooled galvan- ized iron shade was 3° cooler than that under the check shade on the average, and 7° cooler during the hottest part of the day. This lowering of the radiosity of the surround with shades will decrease the radiant-heat load on the animals from 176 Btu per hr. per sq. ft. of animal sur- face with the uncooled check shade, to 165 with the wetted galvanized iron shade, and to 157 with the wetted burlap shade. In other words, a 700-pound steer with a surface area of about 42 sq. ft. exposed to radiation would receive 462 Btu per hr. less under the wetted galvan- ized iron shade than under uncooled sur- face shade, and 798 Btu per hr. less under Fig. 9. Shades with surfaces cooled by evaporation of water used in 1948 tests. Shade at left has burlap sub-roof; right hand shade galvanized iron sub-roof. the wetted burlap shade. This calculation is based upon observations made at 11:30 A.M., September 1, 1948, when the ambient air temperature was 101° F. The effect of the two cooled shades and the galvanized iron check shade was evaluated by a 54-day feeding trial. On July 28, 17 good quality Hereford steers and 6 good Braford steers were divided among the three pens. Throughout the test period these animals were fed all the good alfalfa hay they would con- sume, and during the last 27 days they received, in addition, 1 pound of barley per head daily. The data on weights and gains are shown in table 4. Two Brafords were assigned to each shade. All gained at approximately the same rate. Their greater heat tolerance apparently made them less sensitive to differences in types of shades. Inclusion of these animals made it impossible to ascertain the feed consumption of the Herefords. The weight-increase data in the table are for the Herefords only. During the test, one Hereford in the pen with the galvanized iron roof died from an undetermined cause, and this animal is not included in the results. The Herefords under the hay and galvanized iron roofs gained at the most rapid rate, 0.89 pound per head daily, and those under the plain galvan- ized iron shade gained the least, 0.69 pound per head daily. The animals under the aluminum and burlap roofs made daily gains of 0.80 pound. However, one animal under the wet burlap shade was sick during most of the experiment, and if he is eliminated from the calculations, the rate of gain would be 0.90 pound. Drip from the wet burlap roof kept the animals damp, and they seemed to be more comfortable than the animals in the other pens. The concrete floor under this shade had to be cleaned several times a week and sanitation was a problem. The animals under the plain galvanized iron shade suffered the most, as evi- denced by increased panting, driveling, and smaller gains. On a particularly hot day, when the air temperature at 3:00 P.M. was 118° F and the relative humidity 15 per cent, the average respiration rates per minute under the three shades were: galvanized iron, 116; double roof with galvanized iron, 105; and double roof with burlap, 80. Brafords usually had about as many respirations per minute as the Herefords, but their breathing was much shallower. On this very hot day the Brafords aver- aged a few respirations more per minute than the Herefords, but their degree of suffering was much less. All the measurements taken during this test show the two wetted shades to provide a cooler environment for the Table 4 — Comparison of weights and gains of Hereford steers with three different types of shade materials (July 28-September 20, 1948) Type of shade Number of Herefords Average* initial wt. July 28 (lb.) Average* final wt. Sept. 20 (lb.) Average daily gain (lb.) Feed/100t lbs. gain (lb.) Galvanized iron roof Aluminum and burlap roof ... Hay and galvanized iron roof. 5 6 5J 430 429 420 467 472 468 0.69 0.80 0.89 1230 1266 1091 * Average weight and gains are only for the Herefords since there was no significant difference between the Brafords. t Feed per 100 pounds of gain includes feed eaten by the Brafords. t One Hereford died. [24] steers. The steers under these two shades were more comfortable, gained about 0.20 pound more than the check pen, had lower respiration rates, and did less driveling. Nevertheless, the increases in gain do not seem to be enough to com- pensate for the higher cost of construct- ing double-roofed shades and the extra work of keeping the pens sanitary. High and Low Shades, 1948-1949 At another corral were two shades, identical except for height; one was 7 feet high to the underside of the roof, while the other was 12 feet high. Both were 18 x 36 feet and were covered with hay supported by wire (fig. 10) . A group of animals on pasture had access to these shades and showed a decided preference for the 12-foot one. Measurements with a flat-plate radiometer showed that the high shade cut off 64 per cent of the total solar and sky radiation at noon as com- pared to 61 per cent for the low shade. In 1949, the experiment with the low and high shades was repeated, but the corral was rebuilt so that the exit to the pasture was the same distance from each shade, and a water tank placed in line with each. A manger for hay was set up between the two, so that it did not cast a shadow in either of the shaded areas. Thus, the two shades were equally convenient. Eight Hereford steers aver- aging 650 pounds used these shades. They were fed about 13 pounds of al- falfa hay per head daily along with the alfalfa pasture, and gained 1.57 pounds per head daily during the test period (July 12-September 16) . The high shade was used almost exclusively. Observations in 1948 under several experimental shades showed that the type of shade has very little effect on the air temperature under the shelter, un- less water is evaporated into the air from sprays or from urine and feces. A more complete test was made in 1949 with the 7-foot and 12-foot shades. Using a 16-point recording potentiometer, a ! -. . *€- ' Fig. 10. Hay-covered shades, one 7 feet and the other 12 feet high to the underside of the roof. continuous record of air temperature at several levels was obtained under these two hay-covered shades for 48 hours. Thermocouples of 30-gauge copper-con- stantan wire were supported from the roofs at heights of 1, 3, and 6 feet under the low shade and at 1, 3, 6, 9, and 11 feet under the high shade. The supports were moved hourly so that the bottom thermocouple was always close to the center of the shadow. At night all junc- tions were left directly under the center of the shade. While there was some evi- dence of stratification at higher eleva- tions, at the 1- and 3-foot levels, occu- pied by the animals, there was little dif- ference between the two shades. Most of the benefit, as far as animal comfort is concerned, should be ascribed to a lower- ing of the radiation heat load. Louver Shade A louver shade was also tested in 1949. The louvers were set at such an angle that a solid shadow was cast on the ground but allowed almost total exposure of the animals to the colder north sky (fig. 11). The angle and spacing of the slats (1 x 10-inch boards) were calcu- lated for the latitude of El Centro at noon of the longest day. The over-all size of the shade was 13% x 22 feet. At first this shade was 6 feet above the ground, but later it was raised to 9 feet. This [25] shade was compared with the galvanized iron shade and the hay-covered shade with a sub-roof of galvanized iron, but no water was used for cooling. Animal preference was used as an in- dicator of the effectiveness of these three shades. The test animals included eight Hereford and eight Braford steers, aver- aging about 650 pounds each. They had access to pasture and, in addition, were fed an average of 6.4 pounds of good alfalfa per head daily. The Herefords made an average daily gain during the 66-day test period (July 12 to September 16) of 1.20 pounds, while the Brafords averaged 2.13 pounds. The cattle came in from pasture about 7 a.m. and went out again between 4 and 5 p.m. Gates of the corrals were left open, giving all the animals free choice of the shades. Their preferred resting place was the double-roofed shade. The galvanized iron shade was never used and the louvered shade only occa- sionally, although both were more con- veniently located relative to feed. About halfway through the test, the louvered shade was raised from 6 to 9 feet, but the preference of the steers remained the same. A comparison of the energy incident on a flat surface was made by means of a hemispherical radiometer at noon on Fig. 1 1. Louver shade. August 24 when the air temperature was 106° F. The double-roof shade cut out 58 per cent of solar and sky radiation at the center of the shadow; the galvan- ized iron shade, 54 per cent; and the louvered shade, 53 per cent. The south end of the louvered shade cut off even less energy (51 per cent). By the use of a directional radiometer, traversing from the north horizon through the zenith down to the south horizon, it was found that the high-intensity radiation was energy reflected from the top side of the louvers down onto the steers. A person standing under the shade could feel the concentration of energy on the face and body from the north side. Raising the shade to 9 feet gave the same effect, al- though intensity was less at cow level. Trees for Shade Trees have been suggested as provid- ing the "ideal" shade. Because of their irregular shape, their comparative value is difficult to measure. A limited number of observations at Davis indicate that their radiosity may be somewhat less than for a flat aluminum shade. A large black walnut tree averaged 138 Btu per hr. sq. ft. when viewed from the shadow beneath it; a smaller catalpa tree aver- aged 141 Btu, and an aluminum shade, 170 Btu. At this time the air temperature was 83° F, with a slight breeze. One distinct advantage of trees is the fact that, because of their thickness of mass of leaves, their shadow is always larger than the vertical projected area, giving a larger low-temperature ground area with a given exposure to cool sky than is possible with a thin shade. Disadvan- tages of trees are that in many cases the shadow is not solid because of openings between leaves, and that they do not fit into practical farming practice where it is desired to rotate pastures frequently. Painted Shade Materials Certain materials, such as white paint, are highly reflective (low absorptivity) to short-wavelength radiation and are Fig. 12. Three 8 x 8 x 4-feet-high test shades set up over a dirt field. Note black-globe ther- mometers at center of each shadow and in sun. very good emitters (high emissivity) of long-wave radiation at their normally low temperatures. In the study described below, white-painted aluminum sheets were as much as 15° cooler than un- painted aluminum sheets when exposed to the sun. White-painted galvanized iron sheets were as much as 50° cooler than unpainted ones. While the characteris- tics of the top surface greatly influence the temperature of the shade material, it is the emissivity of the bottom surface that influences the quantity of energy, due to this temperature, that will be emitted to the animal. The reflectivity of the bottom surface determines the quan- tity of incident energy, from the ground, that will be reflected back down to the animal. To study the thermal effects of changes in radiation characteristics induced on the surfaces of various shade materials by painting, field tests of several ma- terials were conducted during the sum- mers of 1952 and 1953. Three flat, port- able shade frames, 8x8x4 feet high, were covered with the materials tested. The frames were collapsible so that they could be easily moved (fig. 12). One frame was always covered with plain cor- rugated embossed aluminum roofing to serve as a check shade. The real thermal comparison of two shades should be based on the relative comfort of animals under them. To ob- tain such comparisons, one 6-inch black- globe thermometer was placed under each of three shades and kept in the cen- ter of the shadow. A fourth globe was placed in the sun to serve as a basis for comparison. The temperatures of the shade materials were obtained with thermocouples attached to the under- surface of the shades. Temperatures of both the globes and the thermocouples were continuously recorded by a 16-point recording potentiometer. The quantity of radiant energy from the shade surface and from different parts of the surround was measured with a Hardy radiometer. The upper left-hand section of figure 13 shows the radiant heat load on the globes under three shades covered with corrugated embossed aluminum roofing. One was left unpainted. Two coats of Fuller's Myratic No. 1520 white paint were applied to the top surface of the re- maining two, and the bottom surface of one of these was painted with two coats of Fuller's Myratic No. 1518 vel- vet black paint. The lower set of curves shows the surface temperatures of these three shades. White paint and the unpainted alu- [27] mmum sheet reflect about the same amount of solar energy (about 75 per cent), but the emissivity of the white paint at ordinary shade material tern- perature, is much greater (about 0.89) (0.11 to 0.20). The white-painted sur- tace consequently maintained a lower temperature because of better radiation exchange with the cold sky. Since the radiation characteristics of the bottom surfaces were identical, the radiant heat load under the white-painted shade was considerably less. The surface temperature of the third shade, painted white on top and black underneath, was about the same as that of the white-top shade, and yet the radi- ant heat load under it was as much as 13 Btu per hr. ft.* less. Since the upper- surface radiation characteristics of these two were the same (white paint) the dif- ferences must be attributed to a rcduc ban of reflected energy under the black- pamted shade. The undesirable effect (greater emission by the black surface) was less than the desirable effect (re- duced reflection of incident energy) The black surface absorbed more radii ion from the unshaded ground than did he unpamted surface, but at the same bme it lost heat at a greater rate by radiation to the cool shadow. Further- more, convection cooling would tend to prevent an excessive temperature rise of the black surface. The surface temperatures of the painted shades were at times 15° lower than that of the unpainted shade. The radiant heat load under the white and Wack shade was as much as 18 Btu per shade ■" tha " U " der tHe un P ai "ted Hay has invariably proved "cooler" White top I f\ - Black bottom Aluminum Fig. 73. Radiant heat loads uncW 8 y ft v >< t *l . shade was determined from Z^lJlZt T fu' ^^ ^ '° ad ""^ each •he shade materials are also shewn ** ""^ ° f sh " d ° W - Surf °« temperatures of [28] than most other shade materials. One of the shades was covered with a 4-inch layer of hay, and results were compared with the unpainted and the white and black aluminum shades. The curves for this test are shown in the right-hand section of figure 13. The radiant heat load under the hay shade was much lower than that under the other two shades. Here, the hay temperature (bot- tom surface) remained very close to that of the air, and as much as 25° lower than the surface temperature of the plain aluminum shade. The very uneven char- acter of the hay surface evidently acts as a black surface and absorbs most of the irradiation on it from the hot ground, thereby reducing the energy reflected back down to the animal. We do not know what the surface convection co- efficient for the hay is, but, because of the uneven character of the surface, it is probably very high. The hay presumably lost much of its heat to the air by con- vection. Also, because of the insulating value of the 4-inch layer of hay, the bottom surface did not receive much heat from the top surface by conduction. Al- though hay has excellent thermal prop- erties, it does have limitations as a shade material, for it must be replaced peri- odically and does not provide a perman- ent and weatherproof structure. Painted galvanized iron roofing sheets were compared similarly and the same beneficial effects of paints were noted. White paint applied to the top surface of galvanized iron caused a reduction of as much as 50° in its temperature, bring- ing it within a few degrees of the tem- perature of white-painted aluminum sheets. The addition of white paint to the galvanized iron sheet made it a "cooler" shade material than plain alu- minum, establishing a lower radiant heat load beneath it. The difference in radiant heat load and surface temperature among the different shades shown in the curves (fig. 13) will not always be of the same magnitudes. These differences may be less or greater, depending upon many environmental factors affecting the shades, such as wind velocity, air temperature, radiation from the sun and sky, and ground cover. The combined desirable effects of white-painted top surface and black- painted undersurface were shown to help greatly in reducing the radiant heat load on an animal under a flat shade of alu- minum or galvanized iron and should aid in increasing an animal's comfort. White-painted Metal Buildings During the summer of 1955 a study was made of the influence of white paint on the thermal environment within a metal building. The building was 60 x 32 feet, with the long dimension oriented north and south. The exterior of the south end and the south 20-foot section (sidewalls and roof) were painted with a flat white paint (fig. 14). The middle 20-foot section was painted with white paint supplied by the building manufac- turer. The north section and north wall were left unpainted. Temperatures of the different building sections were meas- ured with thermocouples attached to the inside surfaces. Surface temperatures for a 24-hour period are shown in figure 15. Maximum surface temperature re- ductions, due to the white paint, occur- red at 1:00 P.M. when the air tempera- ture outside the building was 100.0° F and inside, 102.5° F. These reductions were: west wall, 25.0° F; west roof, 42.6° F; and east roof, 41.0° F. There was little difference in the surface tem- peratures of the two ends even though the south end was in the sun all day. White paint effectively put the south end "in the shade." There was little difference in the effect of the two types of white paint, but the flat white did show a slight advantage over the building manu- facturer's paint (fig. 15). Since only one building with both painted and unpainted surfaces was used, it was not possible to directly compare [29] Fig. 14. Corrugated galvanized steel building, 60x32 feet. South end and south 20-foot sec- tion painted flat white, middle 20-foot section painted with building manufacturer's white paint, north section and north end unpainted. Fig. 15. Inside surface temperatures over a 24-hour period of the walls and roof of the metal building shown in figure 14. 160 [30] Table 5 — Air temperatures in white-painted and unpainted corrugated galvanized steel building, 60' x 32', Imperial Valley Field Station, 1955 Date Time Inside Air Temperatures, °F. White (measured) Unpainted (theoretical) Temperature difference 6/25 6/25 6/26 1:00 p.m 2:00p.m 2:00 p.m 102.5 100.0 102.5 130.5 116.8 119.8 28.0 16.8 17.3 air temperatures in painted and un- painted buildings. However, by theo- retical considerations it was possible to show what the air temperature of a wholly unpainted building would have to be when heat was transferred to the in- Table 6 — Radiosity (Btu/hr/ft 2 ) of outside surfaces of metal barn and surrounding ground, 2:30 P.M., Imperial Valley Field Station, 1955 Surface West side of barn (sun) East side of barn (shade) Unpainted Manufacturer's white Flat white 231 311 315 275 172 179 184 179 Ground side air at the same rate as in the white- painted building, based on actual tem- peratures of the painted and unpainted sections at a particular time and with no ventilation. This was done and the re- sulting air temperatures are shown in table 5 for three different sets of surface temperature values. To show the ability of the white- painted surfaces to "lose" heat more readily than the unpainted surfaces, and thereby remain at a lower temperature, the radiosity* of these surfaces was meas- ured with directional radiometer. One set of these readings is shown in table 6. The white surfaces in the shade gave off more heat, indicating a greater emission of energy than from the unpainted sur- faces. In the sun the greater amount of energy from the white surfaces indicated both greater reflectivity and greater emis- sivity than the unpainted surfaces — very desirable characteristics in heat-load con- ditions for buildings. * Radiosity — the total quantity of radiant energy leaving a surface per unit time per unit area. The radiosity may be due to energy initially emitted by a surface, to energy reflected from the surface, and to energy transmitted through the surface. [31] THE TESTS SHOWED that good shade will reduce the heat load as much as 50 per cent, and will increase gains Measurements in the tests indicated that properly designed shades will reduce the radiation heat load on an animal 50 per cent or more. Since sky temperature, solar radiation, air temperature, and other factors are never constant, no one shade can be best for all conditions. Size of Shade. Most shades in this area vary from 16 to 20 feet in width and up to several hundred feet in length, depending upon the need. Wide shades cut down on the amount of cool sky radi- ating to the animal, although the larger shadow results in less radiation from the ground. The net result in cooling effect is about the same for both wide and nar- row shades; however, wider shades re- duce the drying effect from solar radia- tion, and unsanitary conditions may develop more easily. Orientation. Most shades in the area are constructed with a north-south orien- tation. This usually allows enough sun- shine under the shade to keep it dry and promote sanitation. East-west orienta- tion allows more animals to be exposed to the cool north sky, and ground tem- peratures are a little lower because the ground is shaded for a greater part of the day. Even though east-west orienta- tion decreases the radiant heat load on the animals, north-south orientation is preferred by cattlemen because it pro- motes better sanitary conditions. Height. Raising the height of a shade gives the animal in the shadow a greater exposure to the cool sky and tends to increase the cooling effect. Cattle were found to prefer a shade 12 feet high rather than one 7 feet high. Although shadow size is not affected by height, the higher the shade the faster the shadow moves during the day. A high shade could lose its effectiveness by casting its shadow outside the corral for much of the day. Higher shades receive sun under them for a longer time during the day than do lower shades, thus keeping the area drier. Moisture under a shade serves to lower the ground temperatures, but keeping just the right amount of moisture under a shade would be very difficult. It is prob- ably more practical to plan on keeping this area on the dry side. Shades betwen 10 and 12 feet high seem to be most practical. Men on horse- back can ride under such shades without difficulty, cleaning equipment can be used, and the animals have a good oppor- tunity to be exposed to the cool sky. Shades higher than 12 feet must make more allowances for strong winds. This makes them more expensive to construct and keep in repair. Shade Material. Hay, galvanized iron sheets, aluminum sheets, and boards spaced 2-inches apart have all been tested as roofing material for shades. Hay is the coolest material tested to date. A 4- to 6-inch layer of hay has an insu- lating effect, and heat from the top does not penetrate through and radiate onto the cattle. Very little heat is reflected back to the animals from the underside of the shade. The underside of a hay roof stays very close to air temperature, thus reduc- ing the radiant heat load. However, using hay as a shade roof does have its prob- lems. Unless it is held together between two layers of wire, it tends to blow away. In a wet country hay can absorb a great amount of water during rainy periods and thus tends to break down the shade support unless it is well built. Even well- constructed hay shades must have the hay replaced periodically. Bamboo, palm [32] fronds, etc., give the same cooling effect as hay. Galvanized steel sheets provide the exposed to the sun were found to have a temperature 20 to 30° higher than air temperature. The underside radiates this heat down onto the cattle. By paint- ing the upper side white with a good chalking white paint much of this prob- lem can be reduced; the galvanized steel sheets then come close to hay- covered shades in the resulting cooling effect on the animals. Galvanized steel and other metal sheets have the advan- tage of being more permanent than hay, and they shed rain during the wet season. Aluminum sheets were found to be good shade material. They reflect much of the solar radiation. White paint was found to improve the reflecting qualities of aluminum as well as galvanized steel sheets. Wood makes a good shade material, but leaving a crack between the boards allows the sun to fall directly on the cat- tle. This produces a hotter environment than a solid shade. Cracks appeared to reduce the fly population under a shade, but all the experiments to date show that a solid shade is definitely cooler. Figs. 16 and 17 show two types of shades that may be used in this area. Although no tests have been conducted on the shade required per animal, a check of the shades used year after year indicate that 60 sq. ft. of shade per ani- mal is practical. Many feeders provide between 40 and 50 sq. ft. of shade, but animals should not be crowded during the summer months. . '■ ::■' Fig. 16. This wooden roofed shade is prac- tical in areas where small whirlwinds tend to destroy hay covered shades. Cracks between boards should be kept to a minimum. Fig. 17. This 11-foot hay shade is supported by cables and the hay is sandwiched between two layers of light fence wire. Note the cable fences. [33] WATER AS A COOLING AGENT Water is an ideal cooling agent; it usually is cheap and abundant, and it can be economically transported to the animals; it is noncorrosive and non- toxic ; it has the highest heat capacity of any of the common liquids (1 Btu per pound/ F) and also the highest latent heat of evaporation (1050 Btu per pound at 70°) . This discussion covers tests over the period 1947-1955 that used water as a cooling agent in four different ways: (a) spraying the animals, (b) cooling the air, (see page 52), (c) cooling the shade surfaces, (see page 22), and (d) cooling the drinking water. Spraying the Animals Spraying dairy cattle with water has been investigated by Seath and Miller (1948). The effect of wallows and rain on water buffalo, Zebu cattle, and sheep was studied in India by Minett (1947). European- and Indian-evolved cattle lack sweat glands as they are found in man. However, they do lose moisture and are cooled by the evaporation of water from the skin, more so than originally thought. Kibler and Brody (1952) have shown that at temperatures above 75° F Jersey and Holstein dairy cattle will lose about two-thirds of their insensible (la- tent) heat of metabolism through the skin and only one-third by way of the lungs. This evaporative cooling of the body is not enough to prevent discomfort when environmental temperatures are above the critical range (75° to 85° F). At air temperatures of 105° F all heat produced was dissipated by evaporative cooling. Cattle sprayed with water will be cooled by the evaporation of the water from their skin and by conduction when the water temperature is lower than the skin temperature. This was first shown in tests made in 1946, when some pre- liminary studies were conducted with dairy cattle. At an air temperature of about 109° F and a relative humidity of 18 per cent, wetting cows with a garden hose reduced body temperature about 1.5° and slowed respiration rates by about 20 breaths per minute. The spray tests reported herein were conducted each summer, from 1947 to 1952 inclusive, except for 1948. The re- sults are summarized in table 7, together with the number and breed of animals and their initial weights. Water tempera- ture at the nozzles varied from 85° to 95° F in all the tests. Following are brief descriptions and results of the studies, by year: In 1947 three Hereford heifers were housed under a 16 x 24-foot aluminum shade equiped with three shower heads giving a fine spray. The spray heads were 8 feet above the ground. Water pressure at the heads was 30 pounds per sq. in. A concrete slab under the shade carried the waste water to a drain. The animals made little use of the sprays, got only the ends of the hairs wet (not their skins), and did not seem to be getting any meas- urable benefits. One spray head, with the hole enlarged to % mcn to wet the ani- mals to the skin, was then lowered to 6 feet above the ground, cutting down the drift. When the animals were also wetted down with a hose several times, to show them the benefits of standing under the shower, they began to make greater use of the spray. By the end of the summer one animal was standing under the shower about three hours per day. Occa- sionally, even though the shadow move- ment left the showering animal exposed to the sun, it nevertheless stood under the shower even when the air temperature was 109° F (fig. 18). [34] -ill Fig. 18. Yearling Hereford standing in sun, with air temperature at 109°F, in order to take advantage of spray. Suovto Stall To \>Ateq Supply^ /Vaohetic SuovtR MCAD Duoto Clectqic Cell Belay Dlan Sei^tkmh Tmdu Smover Fig. 19. Single shower head controlled by photoelectric cell relay. Plan shows relation between shower stall, shade, and pasture. Section indicates position of relay with respect to shower stall and animal. [35] Wetted animals usually had body tem- peratures 2° or 3° lower than those of dry animals, and lower respiration rates by 20 or more breaths per minute. These animals never used the sprays at night; even when the night temperature did not go below 80° F, they preferred standing in the open, exposed to the cooler sky. The continuous operation of the showers used excessive amounts of water and created unsanitary conditions under the shade, even though the floor was con- crete. Weight records and feed records were too meager in 1947 to indicate any advantage between the spray and check pens. In 1949 (there were no spray tests in 1948) an inexpensive photo-electric cell relay ($30) and an electric solenoid wa- ter valve were used to control the water flow to a single coarse shower head (fig. 19) so that the shower operated only when an animal entered the stall. The shower was installed over an irrigation ditch so that waste water went directly into the ditch. The shower, with standing room for only one animal, was situated between shade and irrigated alfalfa pas- ture. It was anticipated that the cattle would wet themselves at frequent inter- vals when passing to and from the pas- Fig. 20. Shower stall, located over irrigation ditch, in use in tests of 1950. Water flow is controlled by photoelectric cell relay. ture, thus increasing grazing time. The 8 check animals were at the wood corral and had access to pasture. Feed records were not kept on these animals. Several of the 8 test cattle (table 7) used the shower very little, partly be- cause they never learned its comfort and partly because "boss" cows would not let them into the stall. In spite of this, the average daily gain of the test pen during the 66-day feeding period (July 12- September 16) was 0.37 pound per ani- mal greater than the gain of the un- sprayed, check cattle. This difference in gain may have been influenced by the corrals since the shower group was in a wire pen and the check animals were at the wood corral. In 1 950 the shower stall was widened to 6 feet, three shower heads were in- stalled, and the number of test animals was reduced to four so that all would have equal opportunity to shower. All animals used the spray a great deal of the time during the day. They received all the alfalfa and barley hay they wanted but made little use of the pasture. They seemed to enjoy the water and were defi- nitely more comfortable than the un- showered check animals. The check steers were also in a wire pen, had access to pasture, and were fed the same as the test group. The average daily gain during the 80-day feeding trial (June 21-Sep- tember 9) was 0.22 pound greater than the gain of the check animals (table 7). Because of a shortage of irrigation wa- ter the showers were not operated during three or four days of each month. A view of the shower stall in operation is shown in figure 20. In 1951 a test using very fine mist sprays was conducted in a feeding trial with 5 Shorthorns (2 steers, 3 heifers). The check pen had 4 Shorthorns (2 steers, 2 heifers), and both lots were fed at the wooden corrals from July 3 to Sep- tember 27. 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S ^ « 5 ^ •I S 03 0) fi o W O 1! a 11 1 £ 2-° O 00 X c ■o o p „ |E CO tH q ih CO * IO id «* ^ o o o o v?-o tH t-H tH tH CO*-* te rH t-J "^ CO id ^ ^" CO o o o o "73 tH tH tH tH w-^ i s q (N *i °^ o*? tf) Ttf" -«tf CO o o o o Tiro tH tH tH tH N w fa o o S .fe s 2 q q t* -Q a E A O CO ^ CO o id tjJ id tjJ Q. « o o o o 0) tH tH r-l tH o iter amed p.m. t 5 p.m. io q O O fe. 2 ho© oo CO CO ^ "<* o . . N O NH - °^^ ^temperature / 100 — — u g95 Q.90 e t 85 Relative l?urr2idiTy \/ \, \ -r- at /\ ^Ov ^"Veatfeer staTioi? / \^ M, 80 ■ ia 75 \ J Vire pen ( pen. 2)^* — 70 1 ii-ii i 1 mVi i 1 i i i i i i.i i i — 55 50 45 ^ l H551 a 30 — 25 20 12 Aid. 6 12 Moor 6 Fig. 33. Air temperatures in wood and wire corrals and at outside weather station. Relative humidity at outside weather station. [58] Wire-pen temperatures averaged 4.3° lower than at the weather station and 3.8° lower than in the wooden corral. Aver- age relative humidity at the weather sta- tion ranged between 20 and 60 per cent but only 20 per cent during the hottest part of the day (usually around 3 p.m.) . Average diurnal wind velocity is pre- sented in the upper section of figure 34. The wooden corral had an average wind velocity of 1.11 mph while the wire pen had 2.43 mph. The greatest difference usually came around 5 p.m., with an air velocity of 1.34 mph for the wooden cor- ral and 3.36 mph for the wire pen, a difference of 2.02 mph. These records only cover the first two months of the test period, as the wind recorder broke in the wooden corral during the third month. Average wind velocity for the third month at the wire pen was 1.79 mph. The animals in the wire pen had a cooler environment from lower radiation as well as from lower air temperature and greater air velocity. Radiation meas- urements at the center of the shadows, made with globe thermometers on Au- gust 28 and 29, indicated that the radia- tion heat load was less in the wire pen 3.5 3.0 >25 Wire pen ( per2 2) 5 1 I I I I I I I I I I I I 1 I I o u 90 Vood corral (pert >^ ^Nv Water 'supply Q. E I-&5 ^r u^* " • ■ ■ ^^^ ^N*. L. 2 >ao j?---^';' Wire per2(per2 2) > *v K ^ 75 111 1 1- 1 1 1 1 I I I 1 i i i i i 1 i i i i !2Noor2 6 l2Aid. Fig. 34. Upper: Average diurnal air velocities in wood and wire corrals. Lower: Average diurnal drinking-water temperature in the two pens and temperature of water supply. [59] by as much as 9.5 Btu per hr, per sq. ft. of animal surface. Radiation and reflec- tion from the wooden fence were high. At noon a horizontal reading with a directional radiometer pointed north in- dicated a radiation intensity of 212 Btu per hr. per ft. 2 in the wooden corral, as compared to 163 in the wire pen. If the radiation and air-temperature effects are combined into a single rep- resentative environmental temperature (average of mean radiant temperature and air temperature), then the repre- sentative environmental temperature in the wire pen was about 5° less. Similar comparisons of environment during the late summer of 1953 (but at a different location than the 1954 test) showed the environmental temperature in a wire pen to be 5.5° to 6° lower than that in a wooden corral. Radiation observations were made rather late in the season on days when the maximum air temperature was only 97° F (as compared with a season's average of 103.6° F) . It is probable that the effects of corral construction upon radiation heat load showed even greater differences during most of the test period. The drinking-water temperatures for the two pens are shown in the lower sec- tion of figure 31. The wooden corral had an average daily water temperature of 86.3° F, while that of the wire pen was 81.4° F, and the wire pen with the cool- ing tower averaged 70° F. Tap-water temperatures did not vary much through- out the 24-hour period or through the period of the experiment, staying very close to 93° F. Air movement with low humidity cools the drinking water by evaporation, and the cool water in a shallow tank remains available to the cattle because it cannot sink out of reach. However, part of the differences in water temperature shown here can be attributed to the shallow tank being located in a cooler environment (wire pen). Weather during the summer of 1954 was cooler than average, and the hu- midity was a little lower because of an absence of summer thunder showers. These experiments show definitely that proper equipment for cattle can reduce thermal heat load and increase daily gains significantly. Mechanical Air Movement Since there was a difference in air movement of 1.32 mph, between wooden and wire pens, and the difference in daily gain could be attributed to either in- creased air movement or to a reduction in radiation heat load, it was felt ad- visable to study the cooling effect of wind on cattle by mechanically increas- ing the air movement. During the summers of 1955 and 1956 feeding trials were conducted with Here- ford steers for 70-day periods, from July 6 to September 14, 1955, and June 27 to September 5, 1956. Seven steers were fed in each of two similar pens, except the pen without the fan had only five steers in 1956. Two steers were lost to the experiment at the very beginning. The average weight of animals at the start of the test was 670 pounds in 1955 and 651 pounds in 1956. Both pens were about 50 x 50 feet, and each had a 17 x 32-foot shade that was 10 feet high (about 78 sq. ft. of shade per animal). The drinking water was uncooled (about 87° F). The animals were fed twice daily and were given all they would clean up between feedings. One pen each year served as a check pen — that is, a pen with no artificial movement of air through it. For the sec- ond pen, a 42-inch barn-ventilating fan (17,000 cfm capacity) was mounted on top of the 6-foot board fence along the side of the corral from which the pre- vailing wind blew (fig. 35). In 1955 the fan ran 12 hours during the day the first 21 days, then continuously for the remainder of the test. In 1956 the fan ran continuously. The center of the air [60] Fig. 35. This 42-inch barn-ventilating fan (17,000 cfm capacity) was used to cool the cattle by convection. stream was directed down into the cor- ral at about the center of the shade. Air velocity on the animals at the center of the shade was about 350 fpm or about 4 mph. In 1955, at the center of each pen, at animal level, there was a wire pen enclosing a small weather station (fig. 5). These were not used in 1956. These portable weather stations recorded the air temperature, air velocity, rela- tive humidity, and black-globe ther- mometer temperatures at animal level. As shown by the chart, (fig. 36) the distribution of air was quite good and air movement was increased over prac- tically the entire pen. When these air- velocity readings were made, the aver- age velocity of air in the check pen was 50 fpm. Animals naturally stayed under the shade most of the day and so were exposed to a good breeze all day. Since the weather records were not kept for the two pens in 1956, the records re- ported are for the 1955 test, but weight gains, feed consumption, and weather station records are reported here for both years. Over the entire 70-day period (1955) the air velocity at the center of the shade of the check pen was 55 fpm (0.63 mph) . In the fan or windy pen it was 325 fpm (3.7 mph), while at the weather station the air movement was 1.75 mph. Figure 37 shows the diurnal wind velocity for these three locations. There was no dif- ference in relative humidity between these two pens; the relative humidity at the weather station was 46.4 per cent. The average air temperatures in the two pens and at the weather station, over the entire period, were 87.5°, 88.8°, and Fig. 36. Air velocity distribution in windy pen, Imperial Valley Field Station, 8:30 a.m., June 30, 1955. [61] 45 40 £U 3.0 2 2.5 UJ 2.0 > < 1.5 1.0 v^ Fan pen Weather station I 1 1 I 1 I I 1 I I Check pen I 1 1 Fig. 37. Diurnal air velocity in the fan pen and the no-fan pen and at the weather station. 4 TIME 10 I2M 90.3° F respectively for check, windy pen, and weather station. Figure 38 shows these differences for the three lo- cations. In the morning there was very little difference in air temperature, but from noon until approximately 8 A.M. differences of 1° to 5° are noted, and they are lower at the corral in the check pen than at the weather station. These lower temperatures are more marked during the hours of darkness. The tem- perature in the fan pen was only about 2° lower than at the weather station. On August 11, 1955, and September 11, 1956, four Hereford calves were used to check the cooling effect a fan has on body temperatures. Air temperatures at 2 P.M. were 103° and 106° F, humidity 105 U. 95 ~ 5: 85 2 80 75 - - - y / y'~" m "~'~'\\ AIR TEMPERATURES / •' \ \ v / II i \ **•. ^V / — /»•/ /^.^ ■••...„. '••* ' / / > \ _ / RELATIVE HUMIDITY \ Weother stotion-;.^ 1 1 1 1 1 1 1 1 1 1 ! I 1 i i i i i I i i i i 10 I2N TIME 70 5 60 I - 30 Fig. 38. Air tempera- ture, relative humidity in the fan pen, in the no-fan pen, and at the weather station. [62] 26 and 18 per cent respectively. At about 9 :00 A.M. all four calves were tied in the shade without any air movement, and body temperatures were taken at 9:30 A.M. Right after this two calves were moved under the shade where the fan was blowing, and body temperatures were taken as shown in table 13. Both shades and pens were identical. Body temperatures were definitely lower for the calves under the fan. During the time the body tempera- tures were being taken in 1955, skin temperatures were also measured. Each skin-temperature figure shown in table 14 is an average of six readings. Air velocity during this test averaged 400 fpm in the windy pen and 20 fpm in the pen without the fan. As long as air temperature is lower than the surface temperature of an ani- mal, wind has a potential convective cooling effect. If, however, the air is warmer than the surface, the effect re- Table 13 — Body temperature differences of Hereford steers with and without a fan* August 11, 1955 f Calf No. Calf weight Body temperatures, °F. 9:30 a.m.J 10:00 a.m. 10:45 a.m. 12:15 p.m. 2:30 p.m. Fan Average No fan Average 1 2 3 4 602 621 600 554 104.3 104.2 104.25 104.0 104.8 104.40 103.7 104.2 103.95 103.8 103.9 103.85 104.4 104.2 104.30 104.6 103.8 104.20 104.8 104.6 104.70 104.7 104.8 104.75 105.6 104.8 105.20 105.8 105.1 105.45 September 11, 1956f Calf No. Calf weight Body temperatures, °F. 9:30 a.m.:}: 10:00 a.m. 11:00 a.m. 12:00 noon 1:00 p.m. 2:00 p.m. Fan Average No fan Average 5 6 7 8 754 692 587 690 103.8 102.9 103.35 104.4 103.6 104.00 104.8 103.8 104.30 104.4 103.3 103.85 104.4 103.5 103.95 104.6 104.3 104.45 102.4 104.4 103.40 103.4 106.2 104.80 103.0 105.8 104.40 103.7 105.2 104.45 104.0 106.2 105.10 104.1 106.1 105.10 * Air movement averaged around 400 fpm in the fan pen and about 20 fpm in th tests. t August 11, 1955, 2 p.m. air temperature 103°, humidity 26 per cent; Septemb temperature 106° humidity 18 per cent. t Right after their body temperatures were taken at 9:30 a.m. two calves were the fan pen, the other two stayed under the shade in the no fan pen. 8 no fan pen during the er 11, 1956, 2 p.m., air moved to the shade in [63] Table 14 — Skin temperature difference of Hereford steers with and without a fan (August 11, 1955) Air temperature C F. Air velocity (ft. per minute) Time * t 20 (°F) 400 (°F) Difference (°F) 9 :50 a.m 10:30 a.m 12:30 p.m 2:10 p.m.. 92.9 94.3 97.0 99.0 92.5 95.6 98.4 103.5 98.9 102.6 102.7 104.4 96.1 96.8 101.2 101.8 2.8 5.8 1.5 2.6 * Air temperature in low air velocity pen. t Air temperature in high air velocity pen. Table 15 — Cooling effect of a fan on Hereford steers (July 6-September 14, 1955) (June 27-September 5, 1956) 1955 1956 Fan Check Fan Check Number of animals 7 7 7 5 Av. initial weight (lbs.) Av. final weight (lbs.) 669 831 2.32 5.07 2.33 12.07 1.94 669 759 1.29 4.23 1.92 9.12 1.91 645 813 2.40 4.65 2.32 9.86 2.35 657 788 1.87 4.73 2.37 9.07 2.19 Av. daily gain (lbs.) Av. daily feed (lbs.) Barley M.D.B.P.* Alfalfa hay Oat hay Total 21.41 17.18 19.18 18.36 Feed per 100-lb. gain Barley 219 100 521 84 327 149 706 148 193 97 410 98 253 127 485 117 M.D.B.P Alfalfa hay Oat hay Total 924 1330 798 982 * Molasses dried beet pulp. [64] verses so that there is potential convec- tion heating from wind. Studies in cham- bers at the University of Missouri have shown that the surface temperature of dairy cattle increases with an increase in air temperature, but at a slower rate so that the surface temperature is always above air until both come together at about 103° F. Whether this 103° F holds good under natural conditions is not known, but there could be a variation from this point depending on relative humidity, velocity of air movement, and the amount of moisture lost through the skin of cattle. Tables 13 and 14 show that both body temperatures and skin temperatures of the calves were lower in the pen where air velocity averaged 400 feet per minute. Water consumption during these two years did not vary much. Fan-pen ani- mals in 1955 and 1956 drank 13.8 and 11.9 gallons per head per day, while the low-air-movement-test animals drank 12.4 and 12.2 gallons respectively. Weather data for the test periods of 1955 and 1956 are shown in table 1. Al- though the mean temperature of 90.3° F in 1955 was not the highest during the 10 years of these tests, the average mini- mum of 78.3° F was higher than any other year. Only five nights had a mini- mum temperature less than 70° F. In 1955, one of the more humid years, the mean humidity was 46 per cent. Aver- age maximum, average minimum, and mean air temperatures for 1956 were the lowest during the 10 years of testing. Mean relative humidity was 36 per cent, was close to the lowest of the 10 years. There were 21 days in the 1956 period with night temperatures lower than 70°F. The average daily gain for the animals in the check pen in 1955 was 1.29 pounds per day per animal, and they consumed 1,330 pounds of feed for each 100 pounds of gain. Animals ex- posed to the additional wind from the fan gained 2.32 pounds, and it took only 924 pounds of feed per 100 pounds of gain. In 1956 the differences were not as great; the check pen gained 1.87 pounds per head per day and the fan group gained 2.40 pounds. Economy of gain for the fan pen and check lot was 798 and 982 pounds respectively. Both years' differences were significant at the 1 per cent level. The feed intake of the fan pens was higher than the check pens during both years (table 15). Animals were weighed every 14 days in 1956, but the weight gains and air temperature do not show much correla- tion. However, the humid weather in 1955 no doubt raised the night tempera- ture and probably accounts in part for the very low daily gains of the check-pen animals. Lower temperatures and lower humidity in 1956 probably are factors in higher daily gains of the animals in the check lot. [65] THE TESTS SHOWED That mechanical or natural air movement aids thermal comfort Air movement can be increased in two ways. The first method is to allow the natural air currents and wind free ac- cess to the corral area by constructing the pens with wire, cable, sucker rods, pipe, etc. The second method is to use fans to increase the air flow around the animals. Both have given a larger in- crease in daily gain than most other cool- ing methods so far tested. Natural Air Movement Natural air movement can be in- creased by more than 1 mile per hour in the Imperial Valley by proper corral construction. One test showed an in- crease of 0.43 pound in daily gain when the animals in a wire pen were compared to animals in a wooden corral. Figure 39 shows this airy type of construction. Working corrals should be built with wood, since there is enough stretch in wire and cable to allow animals to escape if they become crowded and excited. Mechanical Air Movement Mechanical air movement by the use of fans has been tested two summers; the fan resulted in an increase in daily gain of 1.03 pounds the first summer, and 0.53 pound the second summer. Both pens used in the test were built of wood. Fig. 39. Fence corner showing one type of cable corral construction. [66] The air movement in the pen with a fan averaged 3.7 mph, while that in the check pen averaged 0.63 mph (air movement checked first year only). The fan ran continually and was placed on the south side of the corral so as to assist the pre- vailing wind (fig. 35). Further work needs to be done to de- termine if the fans need to be run only part of the day, the differences in gain a fan will make in a wire or cable corral, and the velocity of air movement most effective for keeping the animals cool. Recent studies by Kibler and Brody (1950) have shown that European cattle lose a considerable amount of water through the skin even though they are not classified as sweating animals like the horse or man. Increasing the air movement around the cattle may facili- tate the evaporation of this skin moisture which would carry away excess body heat. Several tests in which body tem- peratures were taken of animals under a fan and cattle without a fan have shown the ones with the fan to have a lower body temperature. This type of cooling seems to be quite effective. Cooling Air by Evaporation A "desert cooler" under a shade with three sides enclosed (fig. 27) was tested with Hereford and Braford beef cattle. The Brafords did not show a significant difference in gain, but the Herefords un- der the cooled shade gained 0.36 pound more than the check animals. The in- crease in gain was good, but the cost of construction and maintenance of shades of this type and the cost of the "desert coolers" is higher than some other cool- ing methods tested. Temperatures in the shed were rarely less than 10 degrees cooler than the outside air temperature. As later experiments have shown, the in- creased air movement may actually have been of more benefit than the 10° cooler air. RADIATION An animal is exposed to radiation from everything "within sight." The sky is an important source of radiation be- cause it is so large. Parts of the sky, how- ever, are cooler than an animal's surface and may be used advantageously as a cold sink to absorb radiation from an animal. Corral fences, because they are so close, influence the radiant heat lost or gained by the animal. The ground sur- rounding an animal is important both because it is close to the animal and is such an extensive source of radiation. These three surfaces — sky, corral fences, and surrounding ground — are nearly al- ways "within sight" of the animal, so they are potentially important in influ- encing the radiation heat load on an animal. North Sky Directional radiometers provide a means of obtaining the radiation in- tensity at the surface of the earth from areas of the sky. Many traverses over the sky, from horizon to horizon, with a Gier directional radiometer indicate that azimuth orientation has little effect upon sky radiosity throughout the hot part of the day if the instrument opening receives no direct-beam energy from the sun, and if the sky is free of clouds. Angle of elevation above the horizon is important — an angle of 60° is usually the coldest. In figure 40 a series of traverses with the directional radiometer in north- south and east-west orbits is shown for three different times on a cloudless day. [67] At 12 noon, when the radiometer target was 60° above the north horizon, the observations indicated the lowest sky radiosity. This area had a somewhat higher intensity at 10 and 2 o'clock. The same inference can be drawn from the east-west traverse, shown in the lower section of the figure. To cool a building by direct long-wave radiation to the sky, it would seem desirable to have all open- ings designed to have the greatest shape factor or seeing angle with respect to this area in the north sky about 60° above the horizon. By using an emissivity for the sky of 1.0, the effective sky temperatures can be calculated. In figure 41 a series of 116 north-sky temperatures, observed with the Gier directional radiometer, has Fig. 40. Traverses of Gier directional radio- meter in north-south (top) and east-west (bot- tom) directions. been plotted against air temperatures obtained simultaneously 42 inches above the ground. All observations were made between 10:00 A.M. and 5:00 P.M. on cloudless days (less than 10 per cent cloud cover), during the months of July to September. A linear regression curve has been fitted to these points. Its equa- tion is: t s =-81.9 + 1.5 t a , where t s is the temperature of the sky and t a the tem- perature of the air. A difference of about 28° between air and sky is available as a cooling sink at an air temperature of 100° F and of about 22° at 110° F. The extent of cloud cover is the main factor controlling north-sky tempera- tures in the Imperial Valley. Data ob- tained from the Naval Air Station near El Centro indicate that during the hot- test month, August, there were at least 15 days, throughout the period of 1949 to 1954, which averaged less than 10 per cent cloud cover at 2:00 p.m. It has been observed also that even when the south hemisphere may be fairly cloudy, the north sky may be clear because the clouds appear to form in the area to- wards the Gulf of California. The large number of cloud-free days indicates a fairly reliable sink for radia- tion cooling, which should be exploited in the design of livestock shelters for hot climates. Corral Materials In the section "Natural Air Move- ment" (page 66) , results of feeding trials were shown to indicate that animals in a corral enclosed by a wire fence gained more rapidly than animals in a corral surrounded by a heavy wooden fence. This greater rate of gain was attributed to a more comfortable environment in the wire-fence corral. The better environ- ment within the wire-fence corral was due to: (a) a lower air temperature, (b) greater wind velocity, and (c) to less radiation in the pen. Just how much each of these factors contributed to the test results is unknown. In tests previ- [68] 1 1 u 1 1 1 • • «/ ' 1 ' Je ' 0/^ 000 or ^^ o 00 s^ Ll. o o o ^rt> O ^r O "^100 o o O o >^ aoo fcftr «° 00 _, dfir aoo x — o o o o o * Oog LU ^0 / cr o o o 00 v^C / 000 00 / 3 o r » / H o / < o o (T 90 — o / — / LU / a. / / 2 y' o / / UJ H 80 — o ^r o yo o S^ o / / / / /\v Line of equal /^ / ^ temperature < 7n 1 1 1 1/ 1 1 30 40 50 60 70 80 90 100 OBSERVED SKY TEMPERATURE (°F) Fig. 41. Relation of air temperature at ground to effective north sky temperature 60° above horizon. ously described, wherein the effect on animal weight gains of each of these three factors was considered separately (air temperature page 55, wind page 52, and radiation page 67), the benefits from wind were greatest, and from lower radiation, least. However, this should not be considered as an evaluation of the contribution each of these factors made in improving the climatic environ- ment. The levels of differences between the control and test pens, for each of these factors, were unrelated, making comparison difficult. It is somewhat more difficult to com- prehend and measure radiation differ- ences between two locations than wind velocity or air temperature differences. For this reason a detailed study was made in 1953 to investigate the radia- tion difference between wire-fence and wooden fence corrals. Six-inch black- globe thermometers were kept at the center of the shadows of the shades in two pens shown in figure 31. These were used to measure the radiant heat load to which an animal standing in that spot would be exposed. Radiation measure- ments were made with a directional radi- ometer to determine the intensity of en- ergy radiated from different sources and objects in and around the wire-fence and wooden fence corrals. The curves of figure 42 show that the radiant heat load was less in the wire-fence corral — at times as much as 10 Btu/hr. ft. 2 less. Also, the air temperature in the wire- Fig. 42. Comparison of radiation, air tem- perature, and air velocity within the wooden- fence and wire-fence corrals, August 31, 1953. [69] EAST ~^*^^^ o "-^2- Wire *° AVERAGE OF N.,S.,E.,aW. RADIATION J I I I I I I L 7 8 9 10 II I2N I TIME Fig. 43. Comparison of radiation from four directions in the wooden-fence and wire-fence corrals, August 31, 1953. fence corral was less, averaging about 2° lower. Radiation within the two corrals was also studied by taking a series of read- ings with a directional radiometer. With the receiver of the radiometer at a height of 24 inches and at the center of the shadow of the shade, a series of hori- zontal readings was taken to determine the effect of the corral material on the radiation coming from each direction. The results of one series of reading is shown in figure 43. During most of the period shown there was less radiation, in every direction, from the wire fence. During the morning the radiation from the wooden fence on the west was high- est; in the afternoon it was highest from the wooden fence on the east. The posi- tion of the sun affects the amount of energy radiated from the boards — the boards became hotter, and more solar energy was reflected from them, as the sun became more normal to the boards. This was why the west boards radiated more in the morning and the east boards radiated more in the afternoon. Reflectivity of the boards for solar en- ergy was determined by measuring the quantity of solar energy irradiating them and the amount given off by them. These measurements were made with a sola- rimeter selective for wavelengths below 3 microns. Reflectivity of the boards was found to vary from 54 to 90 per cent, with an average value of 70 per cent. Such high reflectivity makes the board fences good potential heat sources. Solar- energy reflectivity of the ground was found to be about 47 per cent — lower than for the boards. This 47 per cent re- flectivity would represent the reflectivity of the wire fence comparable to the 70 per cent reflectivity of the boards be- cause animals inside a wire enclosure would be exposed to ground instead of the wooden fence. The high reflectivity of the ground inside the corral probably accounts for the greater radiation from the south fence (ground reflection re- reflected by the boards) even though the south boards were in the shadow of the sun. The horizontal directional radiometer readings of figure 43 include radiation from the spaces between the boards, as well as from the boards themselves. The actual radiation from the boards, and from the spaces between the boards, was measured in a separate series of observa- tions. The radiation from the boards was found to be considerably greater than the radiation from the spaces between the boards. The spaces would represent the effect of a wire fence because the ac- tual radiation from the wire itself would be insignificant. The corral-fence material actually does have an influence on the amount of radiation an animal in the corral re- ceives. To reduce the radiant heat load on an animal a wire or cable fence should be used for penning animals. Surrounding Crops Ground temperature and radiation are important to the problem of animal com- [70] fort in warm climates. The flat-plate ra- diometer is an instrument that measures the total radiant energy falling on it from the hemisphere above. Measure- ments with this instrument facing both upper and lower hemispheres indicate that energy from the lower hemisphere may be as much as 40 to 60 per cent (ratio of lower hemisphere radiation to upper, table 16) as great as from the upper hemisphere, depending on the type of ground surface. The lower hemisphere radiation is comprised of low-tempera- ture radiation, due primarily to the tem- perature of the ground surface, and re- flected energy influenced by the radiation characteristics of the surface. Table 16 indicates some of the characteristic dif- ferences between unvegetated ground and alfalfa. Lower hemisphere radiation was con- siderably less over the alfalfa field than over bare ground. The solarimeter meas- ures only the short-wave energy between 0.295 and 3.0 microns. When the sola- rimeter is faced down it measures lower hemisphere short-wave energy only and, consequently, only energy reflected from the ground surface. A comparison of the incoming short-wave energy from the lower and upper hemispheres indicates the reflectivity of the ground surface. Table 16 shows that the reflectivity of the alfalfa is considerably lower than that of the bare ground. Over two adjacent 200- ft.-square plots the air temperature over alfalfa averaged 5° lower at mid-day than over plowed ground. At this same time the lower hemisphere radiation from the alfalfa was 30 per cent of the upper hemisphere radiation, and from the plowed field 40 per cent. While it would be impractical to main- tain green vegetation under and immedi- ately adjacent to an animal shade, except while pasturing, it may be possible to increase an animal's comfort by selec- tion of the proper type of unvegetated ground surface. Ground surfaces vary in temperature by reason of differences in thermal conductivity, density, and other characteristics. Measurements with a touch thermocouple in the Imperial Val- ley in August, 1947, showed a variance in ground-surface temperatures between areas only a few feet apart. At 11 :00 A.M. when air temperature was only 89° F, the following temperatures were ob- served in the sun: Hard ground, tramped by cattle 124°F Hard ground, in road 129°F Soft ground, not tramped by cattle. ,132°F Dry rotted manure in feed lot 148°F Table 16 — Upper and lower hemisphere radiation over bare ground and over an alfalfa field as measured with a flat plate radiometer (total radiation) and a solarimeter (short wave radiation), Imperial Valley, 1954 Time Upper hemisphere radia- tion, Btu/hr./ft» Lower hemisphere radiation Btu/hr/ft 2 Reflectivity, per cent Total Short wave Total Short wave Ground Alfalfa Ground Alfalfa Ground Alfalfa 9:55 a. m 409 411 447 253 282 272 259 268 277 201 199 198 94 79 62 68 66 25 37 28 22 27 23 9 10:10a.m 1:00 a.m [71] 0} 00 P5 t» O ff fr- ee hi (O N oi id oc o CO t-J r-j CO CC > V a. <-> £ t> O OS CO *tf iH a i a *. tH tH tH cs n o w CO M 3 _>* ^2 CO W fl> ^ tf CO > 9 3 3 t^ H lOO 1 -3 -» B 0} > o CO 6 od to c ; B 8 OS OS 00 CO CC > *s Q ft o ^ 10 3 c CO CO T3 *tf co os q "3 C 6 id 00 rl c ! 3 o s a *H O OS t> CC & i-i i-H ■43 > n g L 01 e8 E e in O ja -Q iq co os io Tt O 00 CD ^ OS r- V, o o os co cc > S> o tH rH > u O 3 *■ - CD L. Sg §1 OS ■«# lO O" During the summer of 1949 tempera- tures of several types ot surfaces were measured (table 17) to show the great variation that can be expected. During the summer of 1951 two iden- tical 12' x 12' portable shades were lo- cated in separate fields, one in an alfalfa field and the other in a plowed field to determine the effect of ground cover on environment. Black-globe thermom- eters were kept at the center of the shadow of each shade, at a height 12 inches above ground, to measure the ra- diant heat load at each location. Addi- tional black-globe thermometers were lo- cated in the sun over each field. The radiant heat load is an integrated measure of the effect of radiation from each part of the surround, sky, shade, horizon, unshaded ground, and shadow upon the total radiation the globe ther- mometer receives. The radiosity (in- cludes both temperature radiation and reflected energy) from each part of the surround was measured with a Hardy radiometer. These values, for one day, are shown in table 18. The cloudless sky is the coolest part of the surround and has the same radiosity with respect to both shades. The radios- ity for the other four parts surrounding the shade over the plowed field is greater than for those surrounding the shade over green pasture, with the exception of the horizon. The radiosity of the hori- zon would be expected to be about the same over both fields because it includes trees, etc., that are equally on the horizon of both shades. The influence of these greater radiosities is reflected in the higher radiant heat loads over the plowed field as determined from black- globe thermometer measurements (table 19). A "low-temperature" ground cover will help to reduce the magnitude of this source of heat. Also, ground temperature influences the temperature of the air over it, so it should be as low as possible; this is evident in the air temperatures over [72] m o t>os(N^ Oi- U3 ^ (C W W 50 ^ CO C i 5 s i-H i-H iH i-H i-H i-H i-H ri i- 1 CM o ■o ■a XI c in n d ci iq ^ a> co co iq oqa CO 6 CO T|i T(< W CO rib ! |H * lO IO lO lO lO ^ CN 0> •- o iH iH i-i tH tH i-H iH i-H r- i k E 0) M 00 M O CO H CO OSff 5 .t! th cn "tf o> id io ^" ih* c > a o to p OiHtHOOOO"^ CN IT 5 •o ^ < MO ocncn t»CO r-l -3 4 5 i-H CN CN i-l iH t-I iH i-H t- I ^ UJ s k 43 *- '■V co co oq co i> a> c» q cc ) 0) in cd oo in t? d in co it i £ CO > o CO [* C* t» t- CO CO H C a tj o .3 s M k w CO X ol © *tf co i> co oq ■** loot TJ i*> ci t> to o *-" oo co >n cc k (1 CO CD t» t« t- CO CO H C s CO z o X 4- ■3 cNcocNi-j[>a>q *-j cn | coo^coot^o 00 ^ £ CO CO t- t- b- CD CO tjt N t} ► r-i t-i rH t-I iH tH iH *-H t- o "0 CO c c3 J3 03 E CO 3 cq a> t> i> cq q co t>-^ k bo H CN O W CO Tji id CO CN i^ CO CO CO CO CO CD ^ -o O Sk ^ 4- ^ q co t- q oq m Tjt o« i 1 Tji o> co od co* ^ t> ""^ C k u I CO CO CO CO CO ^ CN O CN "2 H H rl rl H H r iH i- | **- 3 n CO |H in a o £ D o "5 ■3 T ( 9 I h M O CO £ 4 CO co _o ^ £ « 4 E £ £ £ 3 e £ 3 JJ hohn o« & o. e k ^q t«3 a 3 8 HHHHHNCOCfi H rl |> ►- o <35 Table 19 — Radiant heat load determined from black globe thermometer readings, El Centro, September 11 and 12, 1951 Time Air temperature °F. Grass Dirt Radiant heat load under shade Btu/(hr.) (sq. ft.) Grass Dirt Radiant heat load over open field Btu/(hr.) (sq. ft.) Grass Dirt 9/11/51 10 a.m.. 11a.m.. 12 noon lp.m.. . 2 p.m.. . 3 p.m.. . 6 p.m.. . 9/12/51 la.m.. . 7 a.m.. . 85.0 84.0 85.5 86.0 86.5 86.0 80.5 59.5 66.5 85.5 86.0 85.5 86.5 88.0 87.5 80.0 60.5 66.0 153.5 159.5 156.3 156.3 157.1 156.1 135.0 125.0 137.0 156.2 166.4 170.0 165.0 158.5 157.4 141.2 127.2 138.6 238.4 248.1 230.2 251.8 239.0 226.9 135.3 119.2 202.3 254.7 251.6 244.4 263.3 257.0 242.7 146.8 122.0 204.7 the two fields as shown in table 19. Air temperature 12 inches above the plowed field averaged 0.6° higher for the period shown than over the green field. During the hotter part of the day this difference was 1.5°. Direction of air movement was such that it passed first over the green field so the increase in air temperature occurred as the air moved over 45 feet of the dirt field. Nearby "low-tempera- ture" covers, such as clover or alfalfa, can be very beneficial in keeping down both heat load on an animal and the air temperature. Animals on pasture have this advantage over animals held in a dry lot. Fig. 44. View of a feed yard using hay shades and cable fences which reduces radiation and allows for greater air movement. >*-*-,. , ,„ ,, ,; ^ THE TESTS SHOWED That considering radiation from surrounding areas will pay off in better gains Reduction of Radiation Three surfaces — sky, corral fences, I and surrounding ground — are nearly al- ways "within sight" of cattle in the feed yard and influence the radiation heat load on the animals^ Tests reported in this bulletin show that^here are practical ways of reducing this heat load... North Sky. A series of summer sky radiosity observations taken during the last ten years shows that the north sky (about 60° above the horizon) has an average temperature of 20° to 30° lower than ground-air temperature. Any cloud cover will materially reduce the differ- ence between north sky temperature and air temperature near the ground/ How- ever, the Imperial Valley has a large number of cloud-free days which make the north sky a fairly reliable source of radiation cooling. Even when the south sky is fairly cloudy, the north sky may be clear because clouds appear to form to- ward the Gulf of California. The louver shade, discussed earlier, was one attempt to use the north sky as a cold body to which animals might radi- ate heat. Even though this test was not successful, the authors feel that this method of cooling should be considered in designing livestock shelters for hot 1 climates. Corral Material. The better envir- onment in wire or cable corrals was the result of lower air temperature, greater wind velocity, and less radiation. The contribution each of these made toward improving the environment was not de- termined, but each does contribute to animal comfort. Tests showed the radiant heat load within a wire pen to be as much as 10 Btu/hr. ft. 2 less than in a wooden-fence corral, indicating the effect of corral ma- terial on radiation. Wind velocity in the wire corral was always greater, and the air temperature averaged about 2° lower. The total effect was a reduction in en- vironmental temperature within the wire pen of 5° to 6°. ^Corrals, or cattle pens, should be con- structed of wire or cable to permit free air movement and to aid in reducing the radiation heat load on animals and the air temperature in the pen. Also, build- ings, haystacks, or any major obstacle should be kept away from a corral to permit free air movement through the area and to eliminate radiation that might be reflected from them to the animals, if- Surrounding Crops. Bare ground will radiate more heat than an area planted to a crop. Also, air moving over bare ground tends to become warmer than air moving across a green field. A certain amount of bare ground around corrals is necessary for the roads and alleys, but a crop planted in the vicinity of the feed yard will tend to reduce the air temperature and radiation. Figure 44 shows a feed yard that has provided cattle with a cooler environ- ment. The hay shades are about 11 feet high, which reduces radiation from the sun and still allows animal exposure to the cool north sky. The corral fence is made of cable, which reduces fence radi- ation and allows for free air movement. Haystacks and buildings are away from the corrals. Although the photo does not show it, there is a crop planted around the feed yard. [75] RATIONS FOR SUMMER PRODUCTION The calorigenic effect of food is much greater in ruminants than in animals with a single stomach. One of the chief maintenance requirements for animals in a cold climate is heat to keep the body warm. Roughages have a much higher relative value for heating the body than they do for productive purposes. For in- stance, idle horses can be wintered on rather poor quality roughage alone be- cause of the heat produced through its digestion and assimilation. By the same token, a roughage diet during the sum- mer would tend to make the animals hotter at a time when they are having difficulty getting a balance between the rate of heat produced and rate of heat lost. Heat produced in the body following the consumption of food is known as "heat increment." This is the heat pro- duced in the body by digestion and as- similation of food. As noted above, this heat will warm the body but cannot be used for any other purpose since the body is unable to convert heat into other forms of energy. Even with such easily digested feed as barley, about one-third of the total energy in the digested nutri- ents is lost in the increment of heat, and the losses with hay and straw are much larger (60 per cent for wheat straw.) A summary of several tests, some con- ducted during the summer and others during the winter, with some groups re- ceiving a hay concentrate ration and Table 20 — Comparative gains and estimated gains of summer and winter feeding trials with Hereford steers* Alfalfa Hay Summer Warm Water Alfalfa Hay Summer 65 °F. Water Alfalfa Hay Winter Alfalfa Grain Summer Warm Water Alfalfa Grain Summer 65 °F. Water Alfalfa Grain Winter Number of animals Av. length of trials (days) Av. initial weight (lbs.) . . Av. final weight (lbs.) . . . Av. daily gain (lbs.) Av. daily feed (lbs.) Barley 21 77 814 890 0.97 18.4 1.7 20 77 810 909 1.27 19.4 1.8 11 131 662 890 1.74 16.0 1.8 21 75 732 849 1.58 4.4 2.2 9.9 2.0 21 75 740 877 1.83 5.1 2.4 10.2 2.3 16 84 810 1004 2.31 6.7 2.8 10.6 1.9 M.D.B.P.§ Alfalfa hay Oat hay Total 20.1 21.2 17.8 18.5 20.0 22.0 TDNf 10.26 2.14 1.50 10.82 2.26 1.70 9.07 1.88 1.50 11.10 1.69 1.70 12.09 1.80 2.00 13.66 1.99 2.20 DCP| Estimated gain * All summer feeding was done in the warm environment of the wooden corrals during July, August and the first part of September. Winter feeding was done from January through most of May. Each test includes at least three feeding tests. f Total digestible nutrients. t Digestible crude protein. § Molasses dried beet pulp. [76] others only a hay diet, indicates the low productivity of cattle on a roughage diet during the summer. Possibly the heat increment of a roughage ration is only a partial explanation of these differences in daily gain. These tests are shown in table 20. Each group is the average of at least three experiments. All of the sum- mer feeding was done in the warm en- vironment of the wooden corrals, which produced lower daily gains than would be the case from animals in the cooler environment of an airy wire corral. Sum- mer tests were conducted from the first part of July to about the middle of Sep- tember, while the winter tests ran from January through most of May. Animals in these tests were all Hereford steers. Animals made poor daily gains (0.97 pound) on a hay ration during the sum- mer. Cool water increased these gains to 1.27 pounds and also increased food con- sumption, but the expected gain based on the food consumption (TDM and DCP) shows that they should actually be gain- ing about 0.5 pounds more per day. With a hay and grain diet, the daily gains are 1.58 and 1.83 pounds for warm and cool water respectively; only about 0.15 pound less than the expected gain. During the winter when temperature is not a factor, daily gain for alfalfa hay is 1.74 pounds and 2.31 pounds for the grain-hay ration. These gains are a little above the expected daily gain based on the daily food intake. With a cooler en- vironment than the wooden corrals most animals will make better than 2.00 pounds gain with a concentrate rough- age ration. If two animals are receiving 20 pounds of feed a day and one animal gets one-third of this as grain and the other only hay, the one receiving hay and grain would have about 20 per cent less energy to dissipate as heat and 20 per cent more energy to use for produc- tive purposes than the animal on the hay diet. The animal's efficiency of gain is ma- terially increased during the summer by using a hay and grain diet. Summer gains usually require more feed to make 100 pounds of gain, and daily food con- sumption is also down during the sum- mer. It is just a little more difficult to keep animals on feed during hot weather. Although summer diet seems to be a factor in producing faster gains, cattle still present a difficult problem to feeders trying to improve their production in hot weather. Cattle have a high rate of heat production, as shown by the basal metab- olism of a 765-pound Guernsey cow 48 hours after feeding, which was 62 Cal./sq. m/hr., while a 35-year-old woman only produced 37 Cal./sq. m/hr. (Worstell and Brody, 1953). Along with this high heat production, cattle have a low loss of heat through moisture vapor- ization. Cattle seem to react to low tem- peratures more as arctic species do while man's reactions are like those of tropical species, and there is definitely a basic incompatibility between high productiv- ity and high environmental temperatures for these larger non-sweating animals. It is surprising to note that cows, when kept in constant-temperature rooms with the heat slowly increased from 80° to 100° F, will show a decline in heat pro- duction of 30 to 40 per cent. Part of this decline is due to a decline in feed con- sumption and milk production, which may amount to 25 per cent of the total heat produced. The remainder may be due to a decline of thyroid activity since rats, a non-sweating animal, have a lower thyroxine production at high tempera- tures which decreases their basal metab- olism (Kibler, Brody, and Worstell, 1949). At high temperatures, cattle are hard pressed to keep body function going, but at the mean temperature of 90° F during July and August in the Imperial Valley they are definitely more productive on a hay and grain ration than on a straight hay diet, and this is partly due to heat increment. [77] THE TESTS SHOWED That the proper summer diet will help cattle maintain thermal comfort A diet high in fiber will produce con- siderable energy that will have to be dis- sipated as heat from the animal's body. This phenomenon is much more in evi- dence in ruminants than in single- stomach animals. Although the heat produced in the body following the con- sumption of food is very valuable to cat- tle during cold winters, it is a decided detriment in the summer when animals are having difficulty reaching a balance between heat produced and heat lost. Our tests have shown that using grain and good quality roughages (low in fiber) will allow cattle to make satisfactory gains during the summer. Even when the ration is composed of just good quality roughage they tend to have considerably lower daily gains than would be ex- pected. In these desert areas of California 2.00 pounds of gain per day or better can be expected during the summer months if proper precautions are taken as to diet, water, corrals, and shade. Even so, food consumption and efficiency of gain are lower when compared to winter produc- tion. Some consideration should also be given to having cattle acclimated before summer comes; that is, bringing them into the area before summer starts so they can gradually become accustomed to the heat. It is also desirable to plan a live- stock program so that cattle do not reach a high degree of finish during the middle of summer. It would be better to finish the fattening period just before summer weather begins or during the early fall. A heavy layer of fat reduces the animal's ability to rid itself of excass heat. Costs and Power Consumption Results indicate that most investments in cooling pay off In obtaining results reported in this bulletin, costs of the different treatments were considered, but they were not re- garded as criteria for evaluating the re- sults. The tests reported were all experi- mental and the basic objective was to find the effect of different treatments. However, records of costs were kept, and analysis will show that most of the treat- ments, even as applied experimentally on a small scale, increased the producer's net income. One treatment that did not show an increased return, as applied ex- perimentally, was cooling drinking water by mechanical refrigeration. Although the increase in weight gains was good, cost and upkeep of the equipment offset the value of the increased gains. Costs must often be rationalized care- fully to obtain a true evaluation of ex- perimental results. Cattle drinking cooled water in a hot environment did gain sub- stantially more than cattle drinking un- cooled water. Practical application of this result does not necessarily require the large equipment investment used in the experimental tests. Other methods of cooling water by evaporation (page 41) and nocturnal radiation (page 47) were tried. In some cases the problem may not [78] be to cool water, but to keep it cool. One producer in the Palo Verde Valley, inter- ested in applying these results, was able to get 70° F water from his well, store it in an insulated tank, and pipe it under- ground to his corrals so it would stay cool. With little additional cost, he was able to supply his cattle with cool drink- ing water. Using a fan to increase the air flow over beef cattle during hot weather pro- moted increased daily animal gains. In this case the cost of the fan and its opera- tion, even on an experimental basis, could very easily be justified by the in- creased returns from greater production. Even here, the costs involved are not en- tirely relevant to the value of the results. The tests proved the benefit of increased air flow — the fan was only a means of increasing the air flow. Where location of the enterprise and surrounding struc- tures can be planned and arranged to utilize natural wind, there may be no extra cost involved in applying results of the fan tests. If equipment is installed to cool the air, cool the drinking water, or to in- ', Table 21 — Power use of equipment Cattle treated Electric power use — KW Hr. For season Per day Per animal day Cooling air with desert cooler 1948 7 88 1.63 0.233 Evaporative cooling tower pump 1951 1954 5 7 129 89 1.50 1.49 0.300 0.213* Evaporative cooling tower fan 1954 7 76 2.98 0.426f Refrigerated drinking water 1952 1953 20 13 14 14 1131 786 846 996 17.14 9.36 10.07 14.23 0.857 0.720 0.719 1.0161 1954 1955 Fans in corral § 1955 7 7 974 1207 13.91 17.24 1.987 2.463 1956 * Pump used to circulate water for first half of 1954 season. t Fan used to cool water during second half of 1954 season. j Includes energy for cooling extra water consumed by steers on salt water experimei § During 1955 fan was on 12 hours per day for 21 days and continuously for 49 days tinuously for 70 days in 1956. it. . Fan was on con- [79] crease the air flow, the equipment cost and maintenance will generally be the largest item of the cost increase for cool- ing beef cattle — but not always. While for all tests the "cooler" animals con- sumed less feed per unit of weight in- crease, their total food consumption was greater than that of the "uncooled ani- mals. Increased cost for additional feed may actually be greater than equipment cost. The third cost item is power, if it is required. This, however, is generally small. Actual power used in the tests des- cribed in this bulletin is shown in table 21. The power used varied from 0.23 kw. hr. per animal per day for the desert cooler to 2.45 kw. hr. for the fan, Aver- age power costs on Cailfornia farms are usually considered to be 1% cents per kw. hr., so the power costs in our tests would have ranged from 0.345 cents per animal per day to 3.675 cents. This lat- ter cost is perhaps excessive, but this was for power to run the fan that ran continuously, which was probably unnec- essary. Also, the fan probably would have cooled 30 animals instead of 7. Table 21 also shows how much less power was needed to cool water by evap- oration than by mechanical refrigera- tion. The value of "cooling" beef cattle is greatly influenced by the relationship between beef prices and feed cost. Summer Water Requirements Cattle with cool water or less thermal stress drank less water A daily record of water consumption by lots was kept on many of these test animals, especially on the cold drinking- water lots and check groups. Some of these data have already been presented, but a more detailed accounting is desir- able since water is such an important part of the animal's body. The engineer is also interested in the water require- ments of cattle during the summer. Many of these data are presented in table 22 and show both the average daily water consumption and average daily water consumption per 100 pounds of live weight by periods. In most cases those animals with cool water, or under less thermal stress, drank less water than steers with warm water or in a warmer environment. As noted above, the use of salt in the ration in- creased water consumption in both the warm-and cold-water pens, but no bene- fits could be ascribed to the salt. One pen of Brahmans was fed during the summer (1950) and their water consumption was less than the Herefords even when it was calculated on the basis of gallons consumed per 100 pounds of live weight. A detailed investigation was made of the times when water was consumed by the cattle during 1950 and has been checked with data collected in later years. The general trend has been the same. All groups of animals drank more water on the warmer days than they did on cooler days. This is especially true of the warm-water Herefords. As a further check on this, the average water con- sumption on about 20 days, with a mean air temperature of 83° F or less, was compared with the average water con- sumption on about 20 days with a mean air temperature of 88° F or more. In all cases the water consumption was greater on the hotter days. The warm-water Herefords drank 2.23 gallons per day per head more on the hot than on cool days; the Brahmans 1.30 gallons more; and [80] the cold-water Herefords only 0.49 gal- lon more. Several sets of hourly read- ings of water consumption were taken throughout the test. Most of the water was consumed by the Herefords in two 4-hour periods during the day, 7 a.m. to 11 A.M., and 4 p.m. to 8 P.M. This coin- cides with the times of feeding, 7:30 A.M. and 5 p.m. Both groups of Here- fords drank approximately 1.1 gallons per hour per head during the 4-hour morning period and 1.7 gallons per hour per head in the evening. During the heat of the day, 11 a.m. to 4 p.m., only about 0.4 gallon per hour per head was con- sumed, and, during the night, when the water was fairly cool, the animals drank only 0.3 gallon per hour per head. The Brahmans drank less than these amounts but followed the same trend. The water consumption reported in 1950 is roughly double the observed con- sumption of cool water (50° ± 10°) by non-lactating dairy cows under temper- ate conditions (data cited by Thompson, Worstell, and Brody, 1949). Thus, the high water intake and the high correla- tion of water intake with atmospheric temperature variation in this study con- firm, under field conditons, the results reported by the Missouri workers as ob- tained under controlled conditions of their Climatic Laboratory. Ragsdale, Thompson, Worstell, and Brody (1950) found that Braham cows consumed less water per 100 pounds weight below a constant temperature of 90° F. From 85° F upward the Brahmans increased water consumption rapidly and exceeded, with one exception, the Jerseys and Holsteins. One Jersey consumed huge quantities at high temperatures and kept up her pro- duction. The other Holsteins and Jerseys tended to decline in water consumption at high atmospheric temperature. These high temperatures were constant temper- atures and exceeded those experienced here in Imperial Valley. Water consump- tion varies considerably from one animal to another, and individual reactions may be significant. A recent study by Winchester and Morris (1956) gives the water require- ments of cattle under a wide range of conditions and diets. They point out that water consumption remains rather con- stant between air temperatures of 10° and 40° F. As air temperatures increase to 100° F, consumption increases rap- idly. Water consumption will more than double with a change in air temperature from 40° to 90° F. 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