key: cord-0040264-bak5xj7j authors: Franklin, S.T.; Jackson, J.A. title: REPLACEMENT MANAGEMENT, CATTLE | Health Management date: 2004-11-28 journal: Encyclopedia of Dairy Sciences DOI: 10.1016/b0-12-227235-8/00419-3 sha: 99489b4deb0c6f64e913505db12fdeeec1536f2f doc_id: 40264 cord_uid: bak5xj7j nan Replacements are the future of the dairy industry. Focusing on improving health management of replacements will yield tremendous returns through decreased losses of animals with the greatest genetic potential on the dairy, decreased costs of medication, improved growth rates, improved feed ef®ciency and earlier entry into the milking herd. Health management of dairy replacements begins before the replacements are born. Several factors, such as nutrition of lactating and dry cows, vaccinations of lactating and dry cows, length of dry periods, cleanliness of the calving environment and disease status of the dams, will ultimately affect disease resistance and health of replacements. It is important to note, however, that cows that are overfed tend to have dif®culty calving because of being excessively overconditioned. Cows that are underfed, which results in mineral or vitamin de®ciencies or lack of body condition, may produce inferior and lowvolume colostrum. They also may experience dif®culty calving. Protein de®ciency in cows during the dry period may lead to low birth weights, low metabolic rates and poor vigour of calves, resulting in poor survivability. Some research also indicates that inadequate protein and energy nutrition of the dam results in poor absorption of immunoglobulins from colostrum by the calf. Cows that lose condition during the dry period are also at greater risk of experiencing calving dif®culty. Calves that experience dif®cult births require more time before being able to stand, experience an increase in the time to voluntary suckling and have a decreased ability to absorb immunoglobulins. All these problems result in decreased transfer of passive immunity from the dam to the calf and increased risk of disease in calves. As the degree of calving dif®culty increases, the risk of mortality for calves increases. Proper nutrition of dairy cows during lactation and the dry period will help decrease disease risks for replacements. Vaccinations of the dams will also impact disease resistance of dairy replacements. Proper vaccination of the dairy herd will increase the concentration of antibodies (immunoglobulins speci®c for diseases) in colostrum. Dams may be vaccinated during the dry period against pathogens that are common causes of diarrhoea in calves, such as Escherichia coli, rotavirus and coronavirus. Vaccination of the dams increases the concentration of antibodies against these pathogens in colostrum, thus providing increased protection for calves, resulting in decreased incidence or duration of diarrhoea. Vaccination of the dams during the dry period is more effective for prevention of disease in calves than vaccination of calves at an early age. The immune system of neonatal calves is unable to respond quickly to a vaccination or an infection because the immune system of the newborn is immature at birth. Both numbers and effectiveness of antibody-producing cells are lower in calves at birth than in adult cattle. Therefore, it is important for calves to obtain antibodies against common diseases of calves by consumption of colostrum rather than from an attempt to vaccinate calves at an early age. Vaccination of the dams against pneumonia may also help to decrease the incidence or severity of this disease in replacements. Another important factor that may affect the health of replacements is the length of the dry period of the dam. A dry period that is too short, i.e. less than 6 weeks, may not provide enough time for involution of the mammary gland and preparation for the next lactation. Cows with shortened dry periods produce small quantities of colostrum that may also have low concentrations of immunoglobulins. It is important for health of replacements, therefore, that cows have at least a 6-week dry period for production of highquality colostrum. Management of the calving environment has a tremendous impact on the health of replacements. It is important for calves to be born in a clean, dry environment. Wet, sloppy stalls provide a perfect environment for growth of bacteria. Calving on a grass lot may be the best alternative when the climate is dry and mild. If a maternity barn is used, it is important to clean stalls thoroughly between calvings to prevent transfer of disease. Maternity stalls should only be used for calving and never for housing sick cows. Maternity pens and sick pens should be kept in separate facilities in order to prevent transfer of disease to highly vulnerable neonates and periparturient dairy cows. It is also important for the cows to be as clean as possible at calving in order to prevent calves from contracting disease organisms when suckling or attempting to suckle their dams. Preferably, calves should be separated from dams prior to suckling in order to prevent the calf from ingesting pathogens present on the legs, belly,¯anks or udder of the cow as the calf attempts to nurse. Separating the calf from the dam and feeding colostrum by bottle also ensures adequate intake of colostrum for transfer of passive immunity from the dam. Finally, it is important to know the disease status of cows prior to calving. Diseases such as Johne's disease, bovine viral diarrhoea (BVD), and bovine leucosis virus (BLV) may be passed in utero or through colostrum. Calves should only be fed colostrum from cows known to be free of these diseases. It is important, therefore, to maintain a supply of frozen, high-quality colostrum from cows free of such diseases. The importance for baby calves of adequate consumption of immunoglobulins from colostrum has been reviewed elsewhere (see Replacement Management, Cattle: Preruminant Diets and Weaning Practices). Mortality resulting from lack of consumption of adequate amounts of immunoglobulins is commonly greater than 35% and has been reported to be as high as 60%. Others have indicated a 74-fold increased risk of mortality when calves do not consume colostrum. Along with economic losses from high mortality rates as a result of lack of colostrum consumption, there are also increased costs associated with increased medication and poor feed ef®ciency. Transfer of passive immunity (absorption of immunoglobulins from colostrum) can be determined using commercial kits that measure immunoglobulins in the blood. For adequate protection of calves, blood immunoglobulin concentrations should be at least 10 mg ml À1 . Serum protein concentrations in calves are also highly correlated with the concentration of immunoglobulins in blood and can be used to determine adequate transfer of passive immunity. A hand-held refractometer can be used to measure serum protein; levels greater than 5.0 g 100 ml À1 by 24 h of age indicate adequate consumption of colostrum. The use of colostrum substitutes and replacers may help improve disease resistance in calves when high-quality colostrum is not available. The most prevalent health problem of calves on most farms in the United States is diarrhoea. Organisms such as Cryptosporidium parvum, rotavirus and coronavirus that cause diarrhoea will not respond to antibiotic treatment. For cryptosporidiosis, the only means of prevention is sanitation, which includes controlling¯ies. For rotavirus and coronavirus, the most effective prevention is vaccination of the dam to increase antibodies in the colostrum against these organisms. Other organisms, such as E. coli and Salmonella sp., may be resistant to many of the commonly used antibiotics. Producers often give antibiotics to calves during episodes of diarrhoea in order to prevent secondary infections; however, this practice often does more damage than good, killing bene®cial gut micro¯ora and damaging the gut lining. The ®rst step in caring for calves with diarrhoea is to provide¯uids for hydration and electrolytes for mineral loss, while continuing to provide milk for protein and energy. An electrolyte solution can be fed from 20 min to 2 h after each feeding of milk or milk replacer until faeces return to normal. Secondly, the organism causing diarrhoea should be identi®ed to determine whether antibiotic treatment is needed. Pneumonia is the second most prevalent health problem of replacements, especially for replacements raised indoors. Research has shown that calves raised in individual hutches (plastic, ®breglass or wooden structures providing individual housing) perform very well and have fewer health problems, especially pneumonia, than calves raised in closed buildings. Open-front housing for older heifers should also help prevent pneumonia. Adequate, draught-free ventilation is important for prevention of pneumonia. Hutches, pastures and open-front housing for replacements provide optimal ventilation. In addition, hutches can be moved from location to location, giving producers the opportunity easily to remove old bedding and to break disease cycles. No matter what type of housing is used for replacements, cleanliness, dry bedding and adequate ventilation are essential to decrease incidence of disease. Another important factor for controlling disease in replacements is grouping of heifers. Most producers in the United States house young calves individually. In other areas, housing calves in groups and using mob-feeders is an ef®cient method of rearing calves during the liquid feeding phase. After weaning, calves should be housed in small groups of 10 or fewer until they have successfully made the transition from liquid feed to dry feed and the transition from individual housing to competing for food. Additionally, by housing in small groups (rather than mixing large groups of animals at one time), producers can limit the exposure of calves to disease organisms and match calves more closely by size. As calves age, they can be housed in increasingly larger groups; however, animals should be grouped so there is not more than 50 kg difference in size of animals up to 6 months and not more than 90 kg difference in size for older animals. All dairy producers must actively institute biosecurity measures to prevent introduction of disease into the herd and to minimize spread of disease within the herd. For replacements, it is extremely important to prevent exposure of younger animals to older animals that may have Johne's disease. Exposure is not limited merely to animal-to-animal contact, but also includes articles of transmission, such as manure on hands, clothing and boots of workers, manure from older animals on equipment for feeding and handling replacements, or water that has been contaminated by older animals. In addition,¯ies can transfer diseases from older to younger animals. Producers must determine whether to have a closed herd or to allow introduction of new animals to the farm. If new animals are brought to a farm, the producer should work closely with a veterinary surgeon to determine which vaccinations animals should receive prior to coming to the farm. Once new animals arrive on the farm, or animals return to the farm from contractgrowers or exhibitions, they should be quarantined for at least 30 days. This will allow time to determine if the new animals are likely to become ill and to allow the new animals to be exposed more slowly to any disease organisms currently on the farm. Other potential sources of disease entry into replacements are visitors, vehicles removing dead animals, feed-delivery vehicles, wild and domestic animals, and birds. Within the herd of replacements, diseases can be transferred by using needles on more than one animal or using the same glove to palpate more than one animal. Producers must identify potential sources for transfer of disease-causing organisms within the herd and from outside the herd and institute a management plan to control them. Digestive disorders can occur in dairy replacements, resulting in problems such as acidosis and overeating diarrhoea. Overeating diarrhoea is found in replacements during the liquid feeding phase and may be prevalent in systems using accelerated feeding programmes. This form of diarrhoea can be treated by decreasing the amount of dry matter offered to calves in the liquid diet until the consistency of the faeces returns to normal. Care should be taken to determine whether increased¯uidity of the faeces is caused by overeating or by disease organisms. If caused by disease organisms, treatment should include administration of an electrolyte solution and may require use of antibiotics. Acidosis can occur in replacements if they consume large amounts of grains. Forages comprise the basis for diets for replacements after 3 months of age. Animals that gain access to ®elds of maize or bags of feed by accident will often suffer acidosis leading to laminitis (founder) or even death. Animals that are affected will generally have severe diarrhoea. They can be treated by withholding grain until faeces return to normal, followed by gradual reintroduction of grain into the diet. Several types of internal parasites are found in dairy replacements. Perhaps the most common problem is coccidiosis. Coccidiosis causes diarrhoea, which may be severe, resulting in weight loss, dehydration and anaemia. Animals can be treated with a coccidiostat, such as amprolium, for severe coccidiosis. Coccidiostats such as decoquinate or lasalocid may be included in grain rations or even in milk replacers to help control coccidiosis. Another common internal parasite of calves is Cryptosporidium parvum. This organism causes diarrhoea in young calves at 7±10 days of age that lasts approximately a week. There are no cures for cryptosporidiosis and no means of prevention other than sanitation to decrease the pathogen load. Treatment involves electrolyte solutions along with continued milk feeding. Replacement animals are very vulnerable to internal parasites (especially worms) during their ®rst grazing season. Deworming of heifers yields economic returns in growth rates and feed ef®ciency. Producers should consult their veterinary surgeon to determine the most effective method of treating internal parasites both to decrease the parasite load in the animals and to prevent shedding of eggs onto pastures. Depending on geographical location, different deworming strategies are needed to control internal parasite populations. Producers should be aware that cold temperatures cause larvae to undergo arrest, even when ingested into the host. During this arrested stage, the larvae are resistant to most deworming agents. Many external parasites, including various species of ies, affect health and growth of replacements. Several species of blood-sucking¯ies affect replacements. Horn-¯ies can be a major problem for cattle. They can cause substantial blood loss, transmit diseases including mastitis to replacements and decrease growth rates. Use of forced back rubs is probably the most effective method of decreasing populations of horn-¯ies. Additionally, removal of manure, which is the major breeding habitat for horn-¯ies, helps decrease populations. Another type of¯y, the stabley, breeds in wet feed. Severe infestations of stableies can cause up to a 50% decrease in milk production. Counts of 25¯ies per animal cause economically important losses in milk production and growth. Removal of waste feed from under feed troughs and other areas to decrease breeding areas is the most important mechanism for control. Horseies and deer-¯ies are also blood-sucking¯ies and may be responsible for spread of several diseases but are impractical to control. Common house-¯ies are not blood-sucking insects but feed on muzzles, eyes and open wounds. They can be contaminated with more than 30 viruses and 175 bacteria, as well as other disease-causing organisms. The main form of control for common house-¯ies is sanitation and removal of breeding material because many house-¯ies are resistant to insecticide sprays. Cattle grubs are another parasite common in North America. The main damage to cattle is caused by the migration of the grubs through host tissues and production of cysts on the animals' backs. Growth rates can be adversely affected with infestations of cattle grubs. Appropriate insecticide treatment will kill grubs; however, care must be taken not to administer insecticides when large numbers of grubs may have accumulated in the spinal canal. Killing of large numbers of grubs at once can lead to anaphylaxis in cattle. Other external parasites that may affect dairy cattle include¯eas, lice, ticks and mites. Itchiness and formation of scabs should be examined by a veterinary surgeon who can prescribe appropriate forms of treatment. Many disease occurrences can be prevented or at least minimized by appropriate vaccination programmes. The programme that is appropriate, however, will vary from region to region, and even farm to farm. Establishment of a vaccination programme requires knowledge of diseases prevalent in the area, history of diseases on the farm, history of diseases in the herd, vaccinations used previously in the herd and an assessment of the risk of contracting economically important diseases based on management of the herd (open or closed). Producers should, therefore, consult their veterinary surgeon to develop a vaccination programme appropriate for their animals, management and location. Timing of vaccinations is important for replacement animals. If the colostrum consumed by the calf contained antibodies against the disease organism present in the vaccine, the vaccine will not generate a suf®cient immune response in the replacement animal. Maternal antibodies obtained from colostrum may be present up to 6 months of age, preventing an adequate response to vaccinations. It may be bene®cial to wait until 6 months of age or greater for many initial vaccinations in calves in order to avoid interference from maternal antibodies. Additionally, many vaccines are not effective in neonatal calves because their immune system is not suf®ciently developed to generate a protective response. Common mistakes made in vaccination programmes are lack of booster vaccinations at the appropriate time and lack of frequent vaccinations. If the vaccination protocol calls for an initial vaccination followed by a booster vaccination within 2 to 3 weeks, maximum protection will not be achieved without the booster vaccination. Essentially, the money spent for the ®rst injection is wasted. The second problem, lack of frequent vaccinations, is seen especially with leptospiral vaccines. Leptospiral vaccines should be administered every 6 months to achieve adequate protection. It is also important for heifers to start receiving leptospiral vaccinations at 6 months of age so that they have received two vaccinations by the time they are used for breeding. Health management of replacements requires attention to many different areas, ranging from nutrition and management of late lactation and dry cows to vaccinations of replacements. Health management of replacements is an area that is often overlooked because producers do not see an immediate return on their efforts and prefer to spend their time improving management of the milking herd. For health management of replacements, however, the old saying that``an ounce of prevention is worth a pound of cure'' really holds true. Replacement heifers represent the future of the dairy herd. Herd turnover occurs about every 3 to 4 years. Or, in other words, this rate of turnover translates into an annual culling rate of 25±33% necessitating a supply of herd replacements in the form of heifers. These rather high culling rates produce a signi®cant drain on income because the dairy producer loses in milk income (the cull generally produces more milk than her younger replacement), funds expended to purchase the replacement, and also may lose on the value of the calf born to the replacement depending on its genetic merit. In other words, the cost of a replacement heifer equals her purchase cost or value (if raised on the farm) plus the losses in milk yield (difference in the greater value of the milk from the cow and her replacement for what would be the remainder of the cull cow's lactation) minus the recovery value of the cull (sale price of a cull). As a result, the recovery value of the cull when sold is only about one-third to one-half the cost of purchasing her replacement. The time-sensitive nature of establishing pregnancy in dairy heifers dictates that excellent management inputs are required including the use of various hormones to manipulate the oestrus cycle to achieve pregnancy. Rearing and mating of replacement heifers is a critical step in the survival of the dairy farm because it represents 15±20% of total farm costs. Age at ®rst calving is the single most important variable in¯uencing the costs of raising heifers. Age at ®rst calving Body Condition: Effects on Health, Milk Production and Reproduction. Colostrum. Diseases of Dairy Animals Johne's Disease. Diseases of Dairy Animals Ration Formulation: Dry Period and Transition Rations in Cattle; Lactation Rations in Cattle. Replacement Management, Cattle: Preruminant Diets and Weaning Practices An Introduction to Infectious Disease Control on Farms: Biosecurity. Arlington: American Feed Ingredients Association Biosecurity on Dairies. Arlington: American Feed Ingredients Association Biosecurity of Dairy Farm Feedstuffs Large Dairy Herd Management Internal parasites of dairy cattle Vaccines and vaccination programs Nutrient and immunity transfer from cow to calf pre-and postcalving