UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 BLOAT IN CATTLE 
 
 H. H. COLE, S. W. MEAD, and MAX KLEIBER 
 
 BULLETIN 662 
 
 February, 1942 
 
 UNIVERSITY OF CALIFORNIA 
 BERKELEY, CALIFORNIA 
 
CONTENTS 
 
 PAGE 
 
 Experimental methods and results 6 
 
 The relation of ruminal activity to belching 6 
 
 Ruminal pressure and belching 8 
 
 Studies on the rate of gas formation in the rumen 10 
 
 Nature of gases formed in the rumen 14 
 
 Studies on the artificial introduction of gas into the rumen 16 
 
 Discussion 17 
 
 Excessive gas formation 17 
 
 Toxic-gas theory 17 
 
 Interference with belching 18 
 
 Preventive measures against bloat 19 
 
 Summary and conclusions 20 
 
 Acknowledgments 20 
 
 Literature cited 21 
 
BLOAT IN CATTLE 1 
 
 H. H. COLE, 2 S. W. MEAD, 3 and MAX KLEIBER 4 
 
 Bloat, the overdistention of the first two stomachs with gas, is a serious 
 problem in cattle and sheep production. It offers a real obstacle in the 
 pasturing of legumes such as the clovers and alfalfa. Because, from a 
 nutritive standpoint, legume pastures are particularly valuable, deter- 
 mining how they may be safely used is important. Bloat may occur on 
 
 
 
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 Fig. 1. — The four stomachs of the ruminant (sheep) viewed from the right 
 side. (Eeproduced from: Sisson and Grossman, Anatomy of the Domestic Ani- 
 mals, with the permission of W. B. Saunders Co., Philadelphia, Pa., the copy- 
 right owners.) 
 
 several other succulent feeds, including tubers and roots. Occasionally 
 an individual sheep or cow will bloat on any type of ration. Such animals 
 are chronic bloaters, perhaps for causes other than those considered in 
 this discussion. 
 
 In order to develop sound precautionary measures, one must under- 
 stand the causes of bloat. Our studies, though they do not give a complete 
 answer, clarify the problem considerably. 
 
 For an understanding of the subject, certain facts regarding the anat- 
 
 1 Eeceived for publication May 24, 1941. 
 
 2 Associate Professor of Animal Husbandry and Associate Animal Husbandman 
 in the Experiment Station. 
 
 8 Associate Professor of Animal Husbandry and Associate Animal Husbandman in 
 the Experiment Station. 
 
 4 Professor of Animal Husbandry and Animal Husbandman in the Experiment 
 Station. 
 
 [3] 
 
4 University of California — Experiment Station 
 
 omy and physiology of the ruminant stomachs are important. The four 
 stomachs are the rumen, reticulum, abomasum, and omasum (fig. 1). In 
 bloat, we are primarily concerned with the first two — the rumen and the 
 reticulum — although their free communication (fig. 2) makes them prac- 
 tically a unit. The four stomachs of the cow hold 20 to 40 gallons, the 
 exact amount depending upon the size of the animal. The rumen is by 
 far the largest, accounting for about 80 per cent of the total capacity, 
 according to Schalk and Amadon (ll). 5 
 
 No digestive enzymes are swallowed by the cow in its copious saliva 
 (12) or secreted directly by the rumen (3) . Perhaps this statement is too 
 
 A/r space 
 
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 Fig. 2. — Diagrammatic sketch of the midlongitudinal section of the rumen and 
 reticulum adapted from Schalk and Amadon (11). The opening of the esophagus into 
 the rumen (cardiac orifice) is on the right side of the rumen, as is the opening of the 
 reticulum into the omasum (reticulo-omasal orifice). Note that the rumen and retic- 
 ulum are only partially separated by the rumino-reticular fold; also that the reticulo- 
 omasal orifice is submerged in liquid, whereas the cardiac orifice is not. A syringelike 
 action of the reticulum tends to force freshly swallowed food into the posterior rumen. 
 
 dogmatic, for Wise, Miller, and Anderson (16) have shown that milk 
 undergoes some changes while passing through the mouth and esophagus 
 of the calf. 
 
 Food within the rumen and reticulum is softened and reduced to a 
 pulp by the rhythmic muscular contractions of the rumen and is ground 
 and further macerated by the rumination process. It takes about 60 
 hours to empty the rumen. Bacteria, yeasts, and other microorganisms 
 carry on extensive fermentative and digestive action that results in the 
 liberation of abundant carbon dioxide and methane, or marsh gas, with 
 smaller amounts of hydrogen, hydrogen sulfide, and carbon monoxide. 
 We shall later show how the rate of formation of carbon dioxide and 
 methane is related to the kind and amount of food ingested, and shall 
 also consider some facts regarding the control of the belching mechanism. 
 
 Because of the many similarities between belching and the regurgita- 
 tion of food for rechewing, we should like to consider the whole rumi- 
 
 5 Italic numbers in parentheses refer to "Literature Cited" at the end of this bul- 
 letin. 
 
Bul. 662] Bloat in Cattle 5 
 
 nation process briefly, for the details of its mechanism have been rather 
 completely worked out. On a ration of hay and grain, a cow will ruminate 
 about 6 hours daily. As she spends approximately the same amount of 
 time in eating, she is either eating or ruminating 12 hours out of every 
 24 (11). The amount of rumination depends on the nature of the feed. 
 Mead and Goss (7) found, for example, that cows on grain alone rumi- 
 nated very little. 
 
 Shalk and Amadou (11) have furnished the most exact knowledge 
 regarding the regurgitation mechanism and its control. They showed 
 that regurgitation proceeds as follows : first, an extra strong contraction 
 of the reticulum floods the esophageal opening into the rumen with a 
 soupy material ; at the same time, a strong inspiratory movement, draw- 
 ing air into the lungs, reduces the pressure within the thorax and there- 
 fore within the esophagus (since the esophagus passes through the thorax 
 in reaching the rumen ) . This reduced pressure sucks the soupy material 
 into the esophagus, and finally a reverse-peristaltic wave along the esoph- 
 agus carries the material to the mouth. The cow then squeezes the water 
 out of this regurgitated mass, swallows the water, and continues masti- 
 cation. Obviously, therefore, regurgitation involves the coordinated ac- 
 tivity of the muscles of the reticulum, diaphragm, and esophagus. The 
 muscles of the reticulum are entirely involuntary ; those of the esophagus 
 partly so. Regurgitation represents, then, a finely adjusted reflex act. 
 
 The next question involves the means of bringing on this reflex. As 
 Schalk and Amadon showed, the act can be initiated by scratching the 
 rumen wall with a wisp of hay through an artificial opening made into 
 the rumen of the cow. The feeding of grain alone is not accompanied by 
 a normal period of rumination. This fact is explained by the absence of 
 an adequate amount of fibrous material contacting the wall of the rumen 
 and initiating the reflex. The inference is clear, therefore, that the 
 scratching action of ingested roughage on the anterior wall of the rumen 
 normally initiates rumination. 
 
 No attempt is made here to review the literature on the physiology of 
 the ruminant stomach. Certain papers, however, will prove helpful as 
 a source of references: Quin, van der Wath, and Myburgh (10), Quin 
 and van der Wath (9), and Dukes (3) cite much of the literature on 
 ruminal motility. Washburn and Brody (15) have reviewed that dealing 
 with gas formation in the rumen. Mangold (6) gives a comprehensive 
 bibliography on the digestion of cellulose. Olson (<5) refers to many of 
 the papers on bloat. 
 
 We shall first present the results of our investigations and then discuss, 
 in the light of these studies, the theories on the cause of bloat, together 
 with measures useful in preventing bloat. 
 
6 University of California — Experiment Station 
 
 EXPERIMENTAL METHODS AND RESULTS 
 
 Most of the gas formed within the rumen is expelled by belching. A 
 smaller amount diffuses into the blood stream and is expelled through 
 the lungs. To gain information on the frequency of belching, we recorded 
 the number of audible eructations in a cow over 9-hour periods while 
 receiving daily (a) all the hay she wanted and 5 pounds of grain, (&) 21 
 pounds of green alfalfa alone, and (c) 12 pounds of concentrates alone. 
 The cow was kept on the different rations for at least a week before the 
 observations were made. On the hay and grain ration, the average num- 
 ber of eructations was 10.7 per hour, for the green alfalfa alone 9.3 per 
 
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 Fig. 3. — Diagram of the plug used to close the rumen fistula. When used for gas 
 studies, the glass tube extending through the plug was used to connect the interior of 
 the rumen with a mercury manometer or gas meter. When being used simply to seal 
 off the rumen, the glass tube with its stopper was removed, and a solid cork stopper 
 substituted. The diameter of the glass tube is 8 mm. To seal off effectively the cavities 
 to which the air valves lead, a piece of thick rubber tubing was first pulled over the 
 brass tubing at the center and at the two ends. Then the pneumatic cushions were 
 cemented to this rubber tubing, and wire clamps used to make it more secure. These 
 wire clamps were covered with bicycle tape and then with soft, thin rubber tubing. 
 The brass tube is 6% inches long. 
 
 hour, and for the concentrates alone 5.3 per hour. With all the rations 
 used, there was a definite increase of belching soon after feeding began, 
 and this increased rate was maintained for 2 to 4 hours. As will be shown, 
 the rate of gas formation is increased during this same period, and thus 
 the increased rate of belching is explained. This preliminary observation 
 that belching occurs as frequently on hay and grain as on green alfalfa 
 led to the study of the rate of gas formation. 
 
 The Relation of Buminal Activity to Belching. — In human beings, 
 belching is in part a voluntary act largely dependent upon a simulta- 
 neous contraction of the diaphragm and abdominal muscles, which in- 
 creases the pressure on the stomach and causes the gas to be forced out. 
 In the cow the diaphragm and abdominal muscles do not assist in the 
 act. This fact led to a study of the action of the ruminal musculature 
 itself. Schalk and Amadon (11) recorded ruminal motility in the ox by 
 
Bul. 662] 
 
 Bloat in Cattle 
 
 inserting one or more toy balloons through a rumen fistula and holding 
 the partially inflated balloon against the part of the rumen wall to be 
 studied. By holding two balloons simultaneously against different por- 
 tions of the rumen, they determined the sequence of muscular activity 
 within the rumen. The balloon was attached to a water manometer, and 
 the variations in pressure were recorded on a kymograph drum. This 
 method is satisfactory for determining the sequence of activities within 
 the rumen. Schalk has also recorded the ruminal motility with a movie 
 camera. *" 
 
 Fig. 4. — The plug diagrammed in figure 3 closing the ruminal fis- 
 tula of cow 557. This cow has delivered two normal calves and gone 
 through two lactations since the ruminal fistula was established. 
 
 Since, however, these methods require that the rumen be left open, 
 they prevent determination of the relation between ruminal contractions 
 and belching. We therefore devised a method of recording ruminal pres- 
 sures and, with the knowledge gained by previous workers, were able to 
 relate these pressures to the activity of a given portion of the rumen. This 
 method also allowed us to determine the exact time at which the pressure 
 dropped because of belching. 
 
 In these studies we used a cow with a permanent ruminal fistula. An 
 airtight plug (fig. 3) has been devised for the fistula with a tube extend- 
 ing through it to connect the rumen with a mercury manometer. The 
 shaped pneumatic cushions are made by use of a steel mold. This plug 
 is used to close the fistula at all times (figs. 4 and 5). When experiments 
 are not in progress, it is deflated somewhat so that the opening is not air- 
 tight. If sufficient pressure for perfect tightness is maintained for an 
 
8 
 
 University of California — Experiment Station 
 
 extended period, some necrosis results around the fistulous opening. The 
 pressures were determined simply by connecting the glass tube of the 
 ruminal plug to a mercury manometer with pressure tubing. The changes 
 in pressure were recorded on a kymograph drum. 
 
 Figure 6 shows a pressure curve, with the occurrences of belching noted 
 on it. The drop in pressure due to belching follows a ruminal contraction, 
 although belching does not occur at each ruminal contraction. The exact 
 phase of ruminal motility at which the pressure becomes greatest and 
 belching occurs is most easily determined in the cow during rumination, 
 
 Fig. 5. — A nearer view than figure 4, of the plug closing the ruminal 
 fistula. As shown here, the glass tube extending through the core of the 
 plug is removed if the plug is being used simply as a means of sealing off 
 the fistulous opening. 
 
 for Schalk and Amadon showed that the reticulum is contracted and the 
 rumen relaxed at the moment of regurgitation. There is no appreciable 
 change of ruminal pressure as food is regurgitated ; the rise comes 6 to 
 10 seconds later as the rumen undergoes contraction. Quin and van der 
 Wath (9), studying ruminal pressures in a similar manner, but with a 
 somewhat different type of plug, devised by Quin, van der Wath, and 
 Myburgh (10), have noted that, in sheep, belching is related to ruminal 
 contraction. 
 
 The fact that belching is related to ruminal contraction is important 
 for an understanding of the mechanism. Since, however, belching does 
 not occur at each ruminal contraction, other factors are evidently in- 
 volved. 
 
 Ruminal Pressure and Belching. — The fact that belching occurs when 
 the ruminal pressure is greatest, that is, at the peak of ruminal contrac- 
 
Bul. 662] 
 
 Bloat in Cattle 
 
 Fig. 6. — Tracing of portion of ruminal pressure curve of cow 557 on full ration 
 of alfalfa hay and corn silage, using mercury manometer (January 29, 1937). The 
 bottom line is the time interval in minutes. The points on the middle line indicate 
 when audible belching occurred. The vertical scale represents pressure, 0.5 mm on the 
 graph corresponding with 1.0 mm mercury of pressure. Note that after each belching 
 a drop in ruminal pressure occurred and that this drop in pressure follows a ruminal 
 contraction. The highest pressure point is due to stretching. Stretching, coughing, 
 and so forth, cause greater changes in ruminal pressure than does the contraction of 
 the rumen musculature itself. 
 
 Fig. 7. — Tracing of portion of ruminal pressure curve of cow 557 while oxygen is 
 being added at the rate of 3.6 liters per minute, using mercury manometer (April 13, 
 1937). As in figure 6, the bottom line is the time interval in minutes, the points on the 
 middle line indicate when audible belching occurred, and the vertical scale represents 
 pressure, 0.5 mm on the graph corresponding with 1.0 mm mercury of pressure. Though 
 the ruminal pressure, during ruminal relaxation, is 8 mm mercury above the pressure 
 before oxygen was introduced, belching still occurs only at the peak of ruminal con- 
 traction. 
 
10 University of California — Experiment Station 
 
 tion, indicates the importance of pressure. On this point, further evi- 
 dence was secured by preventing a pressure increase during ruminal 
 contraction. This was accomplished by aspirating gas from the rumen, 
 through maintaining a slight negative pressure, in which case belching 
 did not occur. The apparatus employed was the same as that used in 
 studying the rate of gas formation (fig. 8) . The aspirator is not necessary 
 provided the outlet from the rumen is large enough to allow the gas to 
 escape readily and thus equalize the pressure as the rumen decreases in 
 size by contraction. 
 
 Pressure alone is not responsible for belching, however, as we have 
 demonstrated by artificially increasing the pressure through forcing gas 
 into the rumen. As figure 7 shows, under conditions of artificially in- 
 creased pressure, belching occurred only during ruminal contraction, 
 even though the pressure was greater during ruminal inactivity than the 
 pressure associated with belching under normal conditions. This fact 
 proves that the cardiac orifice guarding the entrance of the esophagus 
 to the rumen is not automatically forced open whenever the pressure is 
 increased to a certain point. Obviously, therefore, the other important 
 factor in belching in ruminants is the reflex opening of the cardiac orifice. 
 The role of the cardiac orifice in belching will be discussed later (p. 18) . 
 
 Studies on the Bate of Gas Formation in the Rumen. — The rate of gas 
 formation with various rations was studied in order to determine whether 
 the frequency of bloat on legume pastures is simply the result of an ex- 
 cessive gas formation. Both a cow with a permanent ruminal fistula (cow 
 557) and a normal cow (cow 622), studied by means of a trocar canula, 
 were used. 
 
 The rate was determined first in the animal with the ruminal fistula. 
 An objection to the results with this animal could be made because, before 
 each test period, the rumen was not sealed from the outside air, and con- 
 sequently the ruminal flora might not be normal. Conceivably, this condi- 
 tion might have affected both the absolute and the comparative amounts 
 of gas formed. Another objection to the results with this animal came 
 to light during the investigation. When, during each test period, the gas 
 from the rumen was sampled and analyzed, the carbon dioxide was some- 
 times distinctly lower and the oxygen higher than most of the analyses 
 found in the literature. As was shown later, however, the total amount 
 of gas formed with the ruminal-fistula animal was very similar to that 
 obtained with the normal animal. 
 
 Figure 8 shows the apparatus used in determining the rate of gas for- 
 mation. To avoid letting fluid pass into the gas meter, a trap was inserted 
 to catch the fluid forced out of the rumen with the gas. A check valve 
 was used to prevent the backward flow of gas during ruminal relaxation, 
 
Bul. 662] 
 
 Bloat in Cattle 
 
 11 
 
 though its use in conjunction with the aspirating bottles is not absolutely 
 essential. In the early studies, when no aspirator was used, air was sucked 
 back through the gas meter from the outside air into the rumen during 
 ruminal relaxation. This fact demonstrated that the pressure in the 
 rumen during relaxation is below atmospheric (actual measurements 
 show it to be —6 to —12 cm of water). According to Quin, van der 
 Wath, and Myburgh (10), there is a "negative pressure" in the relaxed 
 rumen of sheep. The gas meter used is the one commonly employed in 
 metabolic tests. The aspirating bottles (so-called "Mariotte" bottles) 
 were used to draw the gas out more rapidly during ruminal contraction 
 
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 Fig. 8. — Schematic drawing of apparatus used in 
 studying the rate of gas formation. 
 
 and thus avoid belching. Presumably, the suction created by the aspirat- 
 ing bottle might be sufficient to draw air through the esophagus into the 
 rumen. The analysis of gas samples taken during each test period showed, 
 however, that this did not occur, since gas samples drawn from the rumen 
 by this procedure were comparable to those taken directly from the 
 rumen without previous aspiration. 
 
 In actual tests, the aspirating bottle proved unnecessary to prevent 
 belching in the ruminal-fistula cow, whereas it was necessary with the 
 canula in the normal cow because of the smaller size of the canula. The 
 glass tube leading to the rumen through the fistula plug had a diameter 
 of 8.0 mm, as compared with 4.5 mm for the bore of the canula used in 
 the normal animal. Because of the larger opening, gas left the rumen 
 freely during ruminal contraction, so that pressure was not sufficient 
 for belching. The use of the aspirating bottle with a suction of 15 cm of 
 water was enough to prevent belching in the normal animal except on 
 one or two occasions when the canula became partly plugged with rumen 
 contents. 
 
12 University of California — Experiment Station 
 
 We have compared the rate of gas formation on cut green alfalfa, 
 alfalfa hay alone, and alfalfa hay and concentrates. The green alfalfa 
 was cut rather than pastured in order that we might accurately deter- 
 mine the amount consumed. Lactating cows with greater appetites were 
 used so that maximum food consumption occurred, since it is under this 
 condition that bloat is most frequently encountered. The cow was kept 
 on the particular ration to be studied, with excess feed provided, for at 
 least 5 days before observations were made. The amount consumed on 
 the day preceding the test always exceeded the amount on the day of 
 the test, because feed was withheld during most of the test period. On 
 March 18, for example, cow 622 ate 113 pounds of green alfalfa, whereas 
 she ate only 24 pounds in the allotted 2-hour feeding period on the fol- 
 lowing morning during a test run (trial 2, green alfalfa, table 1). On 
 March 24 she ate 12% pounds of alfalfa hay and 21 pounds of concen- 
 trates, whereas on the morning of March 25, during a test run, she ate 
 9% pounds of concentrates and no hay (trial 1, hay and concentrates, 
 table 1). On March 27 she ate 5% pounds of hay and 25 pounds of con- 
 centrates, whereas on the morning of March 28, during a test run, she 
 ate 6 pounds of concentrates and 2 pounds of hay (trial 2, hay and con- 
 centrates, table 1). 
 
 The trocar was inserted in the normal cow every few days with no 
 apparent ill effects. With one cow, in fact, seven insertions were made 
 in one month, after which she continued to consume daily 10 pounds of 
 alfalfa hay and 25 pounds of concentrates. Obviously, therefore, the 
 treatment did not impair her appetite or well-being. 
 
 Table 1 shows the rate of gas formation in the normal cow. Results 
 under comparable conditions with the ruminal-fistula cow were as fol- 
 lows : the average of four trials on green alfalfa was 71.21 liters for the 
 period extending from 11 a.m. to 4 p.m. as compared with 64.04 liters for 
 the normal cow; the average of three trials on alfalfa hay for the same 
 period was 74.27 liters, as compared with 77.04 for the normal cow. In 
 neither animal did gas formation on green alfalfa appear greater than 
 for alfalfa hay or, in the case of the normal cow, for alfalfa hay and con- 
 centrates. In both animals a gradual decline in rate of gas formation 
 began the fifth hour after feeding. The one exception was an increase in 
 cow 622 between 3 p.m. and 4 p.m. on hay and concentrates. The reason 
 for this increase is not entirely apparent. In one instance the cause may 
 have been the plugging of the canula during the previous hour. 
 
 On the basis of these data, bloating on green alfalfa cannot well be 
 attributed simply to excessive gas formation. In fact, the tendency seems 
 to be for less gas to be formed from green alfalfa than from alfalfa hay 
 and concentrates. 
 
Bul. 662] 
 
 Bloat in Cattle 
 
 13 
 
 The rapid rise in gas formation after eating shows why bloating may 
 occur soon after animals are turned onto alfalfa pasture. This rise is 
 more clearly illustrated in figure 9 than in the table, for the amount of 
 gas formed during the period of eating is shown. 
 
 TABLE 1 
 
 Bate of Gas Formation in Cow 622 When Fed Green Alfalfa Alone, Alfalfa 
 
 Hay Alone, and Alfalfa Hay and Concentrates 
 
 (On the morning of the test, the cow was given all she would eat between 8 a.m. 
 
 and 10 :30 a.m. ; in the evening all she would eat between 4 p.m. and 5 p.m.) 
 
 Ration 
 
 Feed 
 consumed 
 8 a.m. to 
 10:30 a.m. 
 
 Feed 
 
 consumed 
 
 4 p.m. to 
 
 5 p.m. 
 
 Gas produced 
 
 fed 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Rough- 
 age 
 
 Con- 
 cen- 
 trates 
 
 Rough- 
 age 
 
 Con- 
 cen- 
 trates* 
 
 11 a.m. 
 
 to 
 12 m. 
 
 12 m. 
 
 to 
 1 p.m. 
 
 1 p.m. 
 
 to 
 
 2 p.m. 
 
 2 p.m. 
 
 to 
 
 3 p.m. 
 
 3 p.m. 
 
 to 
 
 4 p.m. 
 
 4 p.m. 
 
 to 
 
 5 p.m. 
 
 5 p.m. 
 
 to 
 
 6 p.m. 
 
 Total 
 11 a.m. 
 
 to 
 4 p.m. 
 
 
 pounds 
 
 pounds 
 
 pounds 
 
 pounds 
 
 liters 
 
 liters 
 
 liters 
 
 liters 
 
 liters 
 
 liters 
 
 liters 
 
 liters 
 
 Green 
 
 
 
 
 
 
 
 
 
 
 
 
 
 alfalfa: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Trial 1 . . . 
 
 36 
 
 
 
 16 
 
 
 
 14.58 
 
 11.75 
 
 8.61 
 
 9.43 
 
 10.18 
 
 24.43 
 
 38.54 
 
 54.55 
 
 Trial 2... 
 
 24 
 
 
 
 14 
 
 
 
 18.51 
 
 16.24 
 
 17.00 
 
 12.69 
 
 9.09 
 
 
 
 
 
 73.53 
 
 Average. . 
 
 30 
 
 
 
 15 
 
 
 
 16.55 
 
 14 00 
 
 12 81 
 
 11.06 
 
 9.64 
 
 — 
 
 — 
 
 64.04 
 
 Alfalfa hay: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Trial 1 . . . 
 
 6 
 
 
 
 4 
 
 
 
 26 18 
 
 20.32 
 
 15 77 
 
 11.74 
 
 12.74 
 
 23.96 
 
 — 
 
 86.75 
 
 Trial 2... 
 
 5 
 
 
 
 — t 
 
 — t 
 
 15 20 
 
 16.19 
 
 14.02 
 
 10 37 
 
 11.55 
 
 — 
 
 — 
 
 67.33 
 
 Average. 
 
 5M 
 
 
 
 — 
 
 
 
 20.69 
 
 18.26 
 
 14.89 
 
 11.06 
 
 12.15 
 
 — 
 
 — 
 
 77.04 
 
 Alfalfa hay 
 
 
 
 
 
 
 
 
 
 
 
 
 
 and con- 
 
 
 
 
 
 
 
 
 
 
 
 
 
 centrates: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Trial 1 . . 
 
 
 
 9^ 
 
 
 
 5 
 
 14.87 
 
 30.30 
 
 15.72 
 
 1.23| 
 
 22.01 
 
 25.57 
 
 30.98 
 
 84 13 
 
 Trial 2 .. 
 
 2 
 
 6 
 
 
 
 5 
 
 24.81 
 
 19.13 
 
 14 54 
 
 15.39 
 
 29.35 
 
 37.03 
 
 
 
 103.22 
 
 Average. 
 
 1 
 
 1% 
 
 
 
 5 
 
 19 84 
 
 24.72 
 
 15.13 
 
 — 
 
 25.68 
 
 31 30 
 
 — 
 
 93.68 
 
 * The concentrate mixture consisted of 500 pounds rolled barley ,150 pounds dried molasses beet pulp, 
 100 pounds choice cottonseed meal, 8 pounds bone meal, and 8 pounds salt (NaCl). 
 t The canula was accidentally pulled out of the rumen, which terminated this trial prematurely, 
 t The canula became plugged during this period. 
 
 The following incident illustrates the rapidity with which bloating 
 may occur after eating. On September 13 the ruminal-fistula cow was 
 connected to the gas meter for gas-formation studies at 6 a.m. On the 
 day previous she had received 71 pounds of green alfalfa. At 8 a.m. she 
 was given 37 pounds of green alfalfa, and at 8 :50 a.m. had consumed 
 15 pounds. Between 8 :30 and 8 :50 a.m. the glass tube leading to the 
 rumen became partially plugged, and at 8 :50 she was distinctly bloated 
 and uncomfortable. Even though 16.8 liters of gas had escaped from the 
 rumen during this period, the lack of sufficient stimulus to induce belch- 
 ing (see p. 18) had resulted in the retention of sufficient gas in the rumen 
 
14 
 
 University of California — Experiment Station 
 
 to produce marked bloating. Clearing of the glass tubing with a syringe 
 bulb brought immediate relief. 
 
 To determine the relation between the amount of feed consumed and 
 the amount of gas formed in the rumen, the feed intake in one experi- 
 mental animal was lowered to 4 pounds of alfalfa hay daily. On the 
 fourth day of this level of feeding, gas formation was determined as in 
 the trials already described. In the period extending from 11 a.m. to 
 4 p.m., 11.08 liters of gas was formed as compared with an average of 
 77.04 liters for two previous trials on a full ration of alfalfa hay. Thus 
 
 
 
 • / \» ^-*t~- * 
 
 8 00 
 
 Ccw fed 
 
 9-.00 10 i 00 f /I -00 
 
 feed removed 
 
 /ZOO noon /OOPM- 
 
 Fig. 9. — The rate of gas formation on green alfalfa alone and upon alfalfa hay 
 alone in cow 557, expressed in liters per half -hour period. The solid line represents the 
 average of five trials on a full feed of green alfalfa ; the broken line, the average of 
 three trials on a full feed of alfalfa hay. 
 
 a reduction in hay consumed from 25 pounds to 4 pounds daily resulted 
 in a reduction in the amount of gas formed to one seventh. Apparently, 
 therefore, feed consumed has a direct relation to gas formed. It is gen- 
 erally agreed among stockmen that greedy feeders are more likely to 
 bloat than poor feeders ; and one would expect lactating cows or rapidly 
 growing animals to be particularly subject to bloat for the same reason. 
 Nature of Gases Formed in the Rumen. — During the gas-formation 
 studies on the normal cow, we have determined the amount of carbon 
 dioxide, methane, and oxygen present in the gas samples from the rumen. 
 From the gas that flows out of the rumen, a sample is taken by letting 
 mercury flow out of a glass bulb connected to the tube between rumen 
 and testmeter. This gas sample is analyzed in an apparatus which we 
 built especially for this purpose. Carbon dioxide and oxygen content of 
 
Bul. 662] 
 
 Bloat in Cattle 
 
 15 
 
 the sample are first measured by absorption in sodium hydroxide and 
 pyrogallol, respectively, and by determination of the changes in volume 
 at a given constant pressure. The remainder of the sample is then mixed 
 with pure oxygen, and this mixture is slowly pumped through a silica 
 capillary tube which contains a glowing nichrome wire. The combustible 
 gases — especially methane — are oxidized at the surface of this wire. The 
 water and carbon dioxide formed are absorbed by driving the gas sample 
 
 TABLE 2 
 Composition of Rumen Gas in Cow 622 on Different Rations 
 
 Ration and time after feeding 
 
 Sample 
 no. 
 
 Carbon 
 dioxide 
 
 Oxygen 
 
 Methane 
 
 Other 
 
 gases 
 
 Alfalfa hay: 
 
 30 
 
 18 
 20 
 32 
 31 
 29 
 19 
 
 23 
 
 22 
 
 24 
 
 26 
 25 
 
 27 
 
 per cent 
 65 
 
 per cent 
 
 1.8 
 2.0 
 4.4 
 1.4 
 1.0 
 1.1 
 5.8 
 2.5 
 
 2.1 
 11 
 1.6 
 
 2.3 
 
 1.1 
 1.0 
 
 1.1 
 
 1.4 
 
 per cent 
 
 28.5 
 22.0 
 17.5 
 25.1 
 24.6 
 23.7 
 15.7 
 22.4 
 
 24.0 
 21.0 
 
 22.5 
 
 9.2 
 21.3 
 18.9 
 18.9 
 17.1 
 
 per cent 
 4 7 
 
 3.5 hours 
 
 63 
 54 
 73 
 66 
 67 
 45 
 62 
 
 3 
 6 
 2 
 5 
 6 
 9 
 3 
 
 12 7 
 
 
 23 5 
 
 
 3 
 
 
 7 9 
 
 6.0 hours 
 
 7 6 
 
 7.5 hours 
 
 32 6 
 
 Average 
 
 12.8 
 
 Green alfalfa: 
 2.5 hours 
 
 67.5 
 68.5 
 68.0 
 
 68.2 
 69.4 
 73.3 
 72.3 
 70 8 
 
 6 4 
 
 
 9 4 
 
 Average 
 
 7 9 
 
 Alfalfa hay and grain : 
 2.5 hours 
 
 20 3 
 
 
 8 2 
 
 
 6 8 
 
 6.0 hours 
 
 7 7 
 
 
 10 8 
 
 
 
 
 
 through concentrated sulfuric acid and then through sodium hydroxide 
 solutions. The increase of weight of the sodium hydroxide solution is 
 used as a measure of the carbon dioxide produced by the combustion. 
 
 Table 2 presents the results. The amounts of these gases do not vary 
 markedly with the different feeds used. 
 
 Washburn and Brody (15), who have the most complete data on the 
 composition of rumen gases, have shown distinctly that the composition 
 of rumen gases varies more with the time interval after feeding than 
 with the ration. They obtained very similar results with three rations : 
 alfalfa hay alone, alfalfa hay and grain, and grass. In each case, carbon 
 dioxide was reduced from about 65 per cent at 4 hours after feeding, to 
 10 to 28 per cent at 15 to 23 hours after feeding. The percentages of 
 oxygen and nitrogen rose as that of carbon dioxide decreased. The per- 
 
16 University of California — Experiment Station 
 
 centage of methane remained fairly constant. These results were obtained 
 by feeding at approximately the maintenance level. 
 
 Dougherty (2) has suggested that an increase in the amount of carbon 
 monoxide may be a contributing factor in causing death by bloat. As he 
 definitely shows, if carbon monoxide is artificially introduced into the 
 rumen, it will pass into the blood and decrease the oxygen-carrying 
 capacity of the blood. But neither his results nor Olson's (8) indicate 
 that the percentage of carbon monoxide varies with the type of food 
 eaten. 
 
 Olson gives some data on rumen-gas composition of bloated animals. 
 The average of nine samples taken from cows bloated on sweet clover 
 was 61.97 per cent carbon dioxide, 3.61 per cent oxygen, and 18.42 per 
 cent methane. Evidently, therefore, gases from his bloated animals do 
 not differ strikingly from those obtained with our normal animals. As 
 he explains, his oxygen figures are rather high because of the method of 
 collecting samples. 
 
 Studies on the Artificial Introduction of Gas into the Rumen. — We 
 have determined how much gas is produced in the rumen under maxi- 
 mum feeding conditions. The question arises: Do these amounts rep- 
 resent the maximum amount of gas that the cow can expel through 
 belching under normal conditions without suffering serious bloat ? 
 
 Carbon dioxide, methane, and oxygen were introduced separately into 
 the rumen when the animal was on green alfalfa and also when it was on 
 hay and grain. Unfortunately the same cow was not used on the two 
 types of feed. We found that any of these gases could be introduced at 
 the rate of 5 liters per minute and sometimes at the rate of 7 liters per 
 minute for 30 minutes without prostration. In some instances it became 
 necessary, at the higher rate, to discontinue introducing the gas after 
 10 minutes. At times the ruminal pressure rose to 100 mm mercury, but 
 this increase was followed by belching and temporary relief. The intro- 
 duction of carbon dioxide markedly affected respiration ; after ruminal 
 contraction the breathing became periodic and forced. This relation of 
 forced breathing to ruminal contraction has not been explained; it is 
 doubtless involved with belching, which involves both ruminal contrac- 
 tion and an inspiratory movement. 
 
 The most significant finding in these gas-introduction studies is that 
 150 liters of gas can be introduced within a half hour without serious 
 results, whereas it would take several hours for this amount of gas to 
 be formed naturally. 
 
Bul. 662] Bloat in Cattle 17 
 
 DISCUSSION 
 
 The experiments will be discussed in the light of some of the more 
 commonly accepted theories of bloat. 
 
 Excessive Gas Formation. — One commonly accepted theory of bloat 
 is that an excessive amount of gas is formed in the rumen and that this 
 is most likely to occur when cows are pastured on green legumes. Veech 
 (13) assumes, for example, that bloat is due to succulent foods in the 
 rumen, which cause the formation of large quantities of gas. Gallagher 
 (4) states that the rapid formation of a large quantity of gas in the 
 paunch causes bloating. Viljoens (14) suggests that bloat commonly re- 
 sults from an excessive production of gases or from an abnormal accu- 
 mulation due to the absence of active movements of the walls of the 
 rumen. According to Woodward and Dawson (17), any feed that pro- 
 duces indigestion and forms gas in the stomach may cause bloat. Kep- 
 hart (5), surveying the occurrence of bloat on sweet clover over a wide 
 area, reached these conclusions : 
 
 1. Bloat is worse when the clover is succulent. 
 
 2. Bloat occurs most readily when the animal is hungry. 
 
 3. Bloat occurs when water or minerals or both are lacking or low. 
 
 4. Bloating is an individual matter, possibly because some animals are 
 more greedy than others. 
 
 Our results do not support this theory of excessive gas formation : the 
 amounts of gas formed on alfalfa hay and grain exceeded those formed 
 on green alfalfa in a highly succulent stage, generally believed to be 
 most conducive to bloat. In fact, bloat actually occurred during one test 
 period on green alfalfa, though the amount of gas formed, as determined 
 by actual test after this period of bloat, was less than during several other 
 trials on hay alone or on hay and grain. We have shown, furthermore, 
 that amounts of gas far exceeding those formed under any conditions 
 studied may be introduced without serious effects. We conclude, there- 
 fore, that bloat is not caused merely by an excessive gas formation. The 
 amount of food consumed and consequently the amount of gas formed 
 is no doubt a contributing but not the main factor in producing bloat. 
 
 Toxic-Gas Theory. — We have no data to support or disprove Dough- 
 erty's theory that a toxic gas is responsible for death in bloated animals. 
 The evidence on the amount of carbon monoxide formed in the rumen of 
 animals on different rations (2, 8) does not strongly support this view. 
 Dougherty (2), however, has conclusively proved that when carbon 
 monoxide is pumped into the rumen, the gas diffuses into the blood, pro- 
 ducing a condition somewhat similar to bloat. His theory really relates 
 to the cause of death following bloat rather than to the cause of bloat. 
 
18 University of California — Experiment Station 
 
 Interference with Belching. — In our opinion, bloat is caused not by 
 excessive gas formation but by interference with belching. If, for exam- 
 ple, animals are pastured on beet tops, the lodging of a piece of beet in 
 the esophagus results in rapid bloating if it is not removed. Surely this 
 is merely the prevention of the escape of gas through the esophagus. Bell 
 and Britton (1), furthermore, state that if lambs on legume pasture 
 turn on their backs and are unable to rise, bloating occurs rapidly. Under 
 these conditions, apparently, belching is prevented by submergence of 
 the cardiac orifice. Conceivably, bloat on green alfalfa or grain alone 
 may be explained by the fact that the rumen contents, being more liquid, 
 cannot be packed away in the posterior rumen; the cardiac orifice be- 
 comes submerged, and belching is prevented. 
 
 In our opinion bloat most frequently results from absence of the stim- 
 uli necessary to initiate belching. As Schalk and Amadou (11) have 
 shown, regurgitation is a reflex act depending upon the constant scratch- 
 ing of the walls of the rumen by roughage; they induced regurgitation 
 artificially by rubbing a wisp of hay, introduced through a rumen fistula, 
 over the inner walls of the rumen. In our opinion, the belching mechan- 
 ism is controlled in a somewhat similar manner. As we have previously 
 pointed out, belching occurs at the height of ruminal contraction and is 
 correlated with the peak of ruminal pressure. Yet increased pressure in 
 itself does not open the cardiac orifice, for when gas was artificially in- 
 troduced, the pressure frequently rose much higher than in any normal 
 animal, and yet gas escaped only during ruminal contraction. The in- 
 variable occurrence of bloat in ruminants after death also emphasizes 
 that the release of gas from the rumen depends upon a functional reflex 
 mechanism. The cardiac orifice is no doubt opened for gas to escape by 
 a reflex mechanism. A relatively rapid change of pressure, such as occurs 
 during ruminal contraction, is probably important; but in our opinion 
 this stimulus must be augmented by the scratching of the rumen walls 
 with roughage. There is evidence to support this belief : bloat occurs most 
 readily under two conditions — the feeding of grain alone or the feeding 
 of succulent legumes. In both instances the amount of prickly fiber pres- 
 ent is at a minimum. Fibrous roughage is effective because prickly. Thus 
 bloat seldom occurs on rations of hay and grain. As Mead and Goss (7) 
 have shown, nonirritating fiber such as finely ground paper pulp added 
 to a grain ration did not prevent frequent bloating. According to many 
 field reports, if alfalfa hay is deprived of its prickly nature by fine grind- 
 ing, bloat frequently occurs. 
 
 Evidently if the reflex mechanism to induce belching is faulty, the 
 amount of trouble expected from bloat will depend to a marked degree 
 upon the amount of gas produced, which in turn will vary with the 
 
Bul. 662] Bloat in Cattle 19 
 
 amount of feed consumed. If, on the other hand, the mechanism to induce 
 belching is normal, then, as we have shown, the cow can belch not only 
 the maximum amount of gas formed under natural conditions, but even 
 greater amounts. 
 
 One may ask why bloat does not occur so frequently on the grasses as 
 on the legumes. To this question, we must confess, we do not have a sat- 
 isfactory answer. A tentative reply, until experimental work is done to 
 clarify the point, is that grasses are perhaps ingested more slowly than 
 legumes because of the nature of growth. Or lush-growing grasses may 
 be more stemmy than legumes. Very occasionally bloat does occur on 
 rank, succulent grasses such as barley. 
 
 To explain the chronic bloater by this belching-interf erence theory of 
 bloat, we may assume that individuals differ in nervous irritability and 
 that the chronic bloater has a high threshold of irritability. Even coarse 
 roughage in the rumen may be insufficient, in such cases, to stimulate 
 belching. 
 
 PREVENTIVE MEASURES AGAINST BLOAT 
 
 According to our theory, bloat results from a dietary lack of sufficient 
 fiber of proper type to initiate belching. We suggest, accordingly, that 
 enough roughage of a coarse, stemmy nature be included in the diet to 
 overcome this deficiency or to prevent excess eating of succulent foods 
 lacking in fiber. The result may be accomplished by several means, but 
 in certain instances all the suggestions are impractical. 
 
 If animals are being fattened on legume pasture and grain, then 
 chopped (but not finely ground) hay may be mixed with the grain. Some 
 lamb feeders are now following this practice. 
 
 For both lamb and cattle feeding, it may prove desirable to mix grasses 
 with legumes for pasture. According to Bell and Britton (1), "bloat was 
 not a problem in pastures covered with more than 50 per cent of grasses." 
 
 Another desirable practice is to feed cattle, particularly lactating 
 dairy cows, palatable hay before turning them into legume pasture. This 
 practice has been carried on successfully with the milking dairy herd 
 of the University Farm at Davis. One must remember that animals on 
 excellent legume pasture may refuse hay unless it is of good quality. Be- 
 cause, furthermore, cattle consume hay rather slowly, they should have 
 access to it for several hours daily. Lactating cows, which have a stronger 
 appetite than nonlactating cows, will require special precautions. Rap- 
 idly growing animals, too, will be more greedy than mature nonlactat- 
 ing animals. 
 
 In years when luxuriant growth of forage occurs, there is trouble with 
 bloat on the range, particularly when legumes constitute a major part of 
 
20 University of California — Experiment Station 
 
 the forage plants. We do not have a satisfactory solution for this problem 
 of bloat on the range. 
 
 None of our advice on the prevention of bloat is original ; one finds a 
 host of suggestions in the literature. The difficulty has been in determin- 
 ing which of these to follow. We believe that sound experimental evi- 
 dence underlies our suggestions. 
 
 SUMMARY AND CONCLUSIONS 
 
 Pressures within the rumen of a cow were studied by means of a spe- 
 cially devised plug for a ruminal fistula. Belching occurs when the pres- 
 sure is raised in the rumen by means of an active contraction of the 
 ruminal musculature. Increased pressure, in itself, does not force gas 
 from the rumen through the esophagus, as is illustrated by the artificial 
 introduction of gas into the rumen. The amount of ruminal gas formed, 
 both in a cow with a ruminal fistula and in a normal cow, was determined 
 on rations of alfalfa hay alone, on green alfalfa alone, and on hay and 
 grain. The amount of gas formed is more closely correlated with the time 
 after eating than with the nature of the ration and is directly related 
 to the amount of feed eaten. The composition of rumen gas was the same 
 irrespective of the type of feeds used in these experiments. 
 
 The theory is proposed that the expulsion of gas from the rumen by 
 belching is a reflex mechanism dependent upon an adequate amount of 
 fibrous material of a prickly nature. Succulent legumes and concentrates 
 contain a minimum of fiber and are therefore particularly conducive to 
 bloat. Preventive measures consist in the introduction of sufficient fiber 
 in the ration to initiate belching. 
 
 ACKNOWLEDGMENTS 
 
 We are greatly indebted to Dr. G. H. Hart for performing the fistula 
 operation on several animals, for help in several phases of this work, and 
 for much timely advice ; to Mr. J. C. Russell for his capable and loyal as- 
 sistance throughout the experiment; and to Mr. Robert Casady, Mr. Leo 
 Christian, Mr. Carter Anthony, and Mr. Albert Kattenhorn, for then- 
 assistance in early phases of the work. 
 
Bul. 662] Bloat in Cattle 21 
 
 LITERATURE CITED 
 
 1 . Bell, W. B., and John Britton. 
 
 1938. Losses of lambs and cattle on Ladino clover pasture. 17 p. University of 
 California College of Agriculture, Division of Veterinary Science. 
 (Mimeo.) 
 
 2. Dougherty, R. W. 
 
 1940. Physiological studies of induced and natural bloat in dairy cattle. Amer. 
 Vet. Med. Assoc. Jour. 96:43-46. 
 
 3. Dukes, H. H. 
 
 1939. The physiology of the domestic animals. 4th ed. 695 p. (See especially 
 p. 271.) Comstock Publishing Co., Inc., Ithaca, N. Y. 
 
 4. Gallagher, B. A. 
 
 1921. Diseases of sheep. U. S. Dept. Agr. Farmers' Bul. 1155:1-39. (See espe- 
 cially p. 28-29.) 
 
 5. Kephart, L. W. 
 
 1929. Do your cattle bloat on sweet clover? Wallace's Farmer 54:727. 
 
 6. Mangold, E. 
 
 1934. The digestion and utilization of crude fiber. Nutr. Abs. and Rev. 3 : 647-56. 
 
 7. Mead, S. W., and H. Goss. 
 
 1935. Ruminant digestion without roughage. Jour. Dairy Sci. 18:163-70. 
 
 8. Olson, T. M. 
 
 1940. Bloat in dairy cattle. Jour. Dairy Sci. 23 : 343-53. 
 
 9. Quin, J. I., and J. G. van der Wath. 
 
 1938. Studies on the alimentary tract of Merino sheep in South Africa. V. The 
 motility of the rumen under various conditions. Onderstepoort Jour. Vet. 
 Sci. and Anim. Indus. 11:361-82. 
 
 10. Quin, J. I., J. G. van der Wath, and S. Myburgh. 
 
 1938. Studies on the alimentary tract of Merino sheep in South Africa. IV. De- 
 scription of experimental technique. Onderstepoort Jour. Vet. Sci. and 
 Anim. Indus. 11:341-60. 
 
 11. Schalk, A. F., and R. S. Amadon. 
 
 1928. Physiology of the ruminant stomach (bovine). Study of the dynamic fac- 
 tors. North Dakota Agr. Exp. Sta. Bul. 216:1-64. 
 
 12. Schwarz, C, and K. Steinmetzer. 
 
 1924. Beitrage zur Physiologie der Verdauung. Fermentforschung 7:229-69. 
 
 13. Veech, B. C. 
 
 1937. Hoven in cows. Agr. Gaz. N. S. Wales 48:105-7. 
 
 14. Viljoens, P. R. 
 
 1922. Acute tympanitis or hoven in cattle. South Africa Dept. Agr. Jour. 
 5:346-48. 
 
 15. Washburn, L. E., and S. Brody. 
 
 1937. Growth and development with special reference to the domestic animals. 
 XLII. Methane, hydrogen, and carbon dioxide production in the digestive 
 tract of ruminants in relation to the respiratory exchange. Missouri Univ. 
 Res. Bul. 263:1-40. 
 
22 University of California — Experiment Station 
 
 16. Wise, G. H., P. G. Miller, and G. W. Anderson. 
 
 1940. Changes observed in milk "sham fed" to dairy calves. Jour. Dairy Sci. 
 23:997-1011. 
 
 17. Woodward, T. E., and J. It. Dawson. 
 
 1926. Care and management of dairy cattle. U. S. Dept. Agr. Farmers' Bui. 
 1470:1-36. 
 
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