Control and Prevention of Disease in Feedlot Cattle
Control and prevention of disease in feedlot cattle depends on purchasing healthy animals; providing a transportation system that minimizes stress, a comfortable feedlot pen environment, and an adequate feeding system; establishing a good surveillance system; and judiciously using vaccines and, when necessary, antimicrobial agents.
One of the most important considerations in the construction of a feedlot is good drainage. The pens and alleyways should be well drained and easily accessible for scraping the ground surface as necessary. Good drainage requires a 6% slope. To avoid overstocking, each animal should be provided with 18 m2 of space in well-drained land and with 9 m2 in a paved lot.
Cattle need protection from wind, rain, snow, excessive heat, and excessive sunshine. Trees are planted as windbreaks, and buildings and fences are placed so the wind is not deflected into feeding areas or sheds. An open-front shed provides protection from winter storms and hot summer sun. Each animal needs ~1–1.5 m2 of cover. The shed should be open to the south or southeast, and the front should be high enough so the sun strikes the ground at the back on the shortest day of the winter. The back of the shed should be ≥2.5 m high. A covered feed bunk protects feed from weather damage and affords cattle added comfort when eating. Feed remains dry and palatable, and waste is reduced. Shades to provide relief from extreme summer heat are useful in feedlots where this is a major concern during the year.
Environmental concerns about feedlot operations have greatly increased in recent years. Stricter environmental laws require that all feedlot waste and run-off be contained in approved lagoon systems. Pollution prevention plans must be on file with the appropriate government agency. Monitoring, testing, and record-keeping requirements vary from country to country as well as regionally. In addition, foodborne illnesses, particularly those caused by Escherichia coli O157:H7 and Salmonella, have forced the meat-packing industry to change the way beef carcasses are processed. The packing industry has placed pressure on feedlots to provide animals that are as clean as possible.
Transportation or shipping of cattle has long been associated with increased bovine respiratory disease (BRD) in the feedlot, hence the term “shipping fever.” With current improvements in transportation, however, there is no correlation between the distance cattle are shipped and the risk of fatal fibrinous pneumonia in the feedlot. Factors such as weaning, level of immunity, commingling, and other stressors appear more important in the risk of BRD than distance shipped.
Cattle can lose considerable weight within the first 24–48 hr after weaning, during shipment, and after deprivation of feed and water. This loss in body weight (known as shrink) varies from a minimum of 4% in cattle deprived of feed and water for 24 hr to up to 9% in animals transported long distances over a period of 2–4 days or in unweaned, high-risk, lightweight calves. Most of the fluid and electrolyte loss can be restored within a few days if the animals begin to eat and drink normally, but some studies show as few as 35% of high-risk calves consume an appreciable amount of feed the first 24 hr in the lot. Shrink >7% has been associated with increased health problems. The total loss in body weight may not be restored for as long as 3 wk in some highly stressed calves.
Transportation equipment and facilities should meet local standards and be able to transport cattle comfortably regardless of the season of the year. Some countries prohibit the transport of cattle over a certain length of time without unloading for rest, feed, and water. On arrival at their destination, cattle should be examined carefully for evidence of clinical disease or injury. Provision of fresh hay, a small amount of starter feed, and water can help detect those that are anorectic and require closer examination. This is particularly important if unexpected delays in transportation have occurred that increase the level of stress in the animals.
Infectious diseases of the respiratory tract are major causes of morbidity and mortality during the first 30–45 days after arrival in the feedlot. Digestive diseases, especially carbohydrate engorgement, in cattle placed on a high-energy diet within 30 days after arrival in the feedlot are a major potential threat but can be controlled. The acute respiratory disease complex (see Bovine Respiratory Disease Complex) is more difficult to control in feedlot cattle, even under good management conditions.
The major objective on arrival at the feedlot is to get the cattle onto a high-energy diet—which will result in rapid growth—as soon as possible, usually within 21 days, while minimizing the morbidity and mortality associated with acute respiratory disease, other common infections, and digestive diseases associated with adjustments to high-energy diets.
Preconditioning is the preparation of feeder calves for marketing, shipment, and the feedlot environment; it may include vaccinations, castration, and training calves to eat and drink in pens. The concept of preconditioning is based in part on immunologic and nutritional principles. Preimmunization, or vaccination of calves 2–3 wk before shipment from the ranch to the feedlot, was the basis of preconditioning. In addition to vaccination, more recent efforts have been directed toward increasing the number of days weaned before movement and improving management procedures on the ranch, such as genetic selection and nutrition, that assist calves in making an easier transition to the feedlot.
In the USA, preconditioning has been defined by the following elements: 1) weaning at least 30 days before sale, 2) training to eat from a feed bunk and to drink from a tank, 3) parasite treatment, 4) vaccination for blackleg, malignant edema, parainfluenza 3, infectious bovine rhinotracheitis, bovine viral diarrhea (some programs also call for vaccination against Mannheimia haemolytica, Pasteurella multocida, and/or Histophilus somni), 5) castration and dehorning with wounds healed, 6) identification with an ear tag, and 7) sale through special auctions. When preconditioned calves are placed in a feedlot, they usually begin to eat and drink on arrival; if they have not been subjected to unusual stressors, the incidence of disease is minimal. However, daily surveillance is still necessary to identify cases of illness. Because these cattle generally go onto feed more easily than calves that have not been preconditioned, care must be taken not to increase intake too quickly and cause digestive concerns.
When preconditioning is examined on a partial budget basis, the cost effectiveness for the cow-calf producer is generally quite favorable. Calves can gain 2–3 lb/day at a very low cost of gain while not getting fat. The health program “bonus” can add $3–$8/100 lb to the price when calves are sold at large, special preconditioned sales, but the primary financial reward to the cow-calf producer is in the form of added weight sold at a low cost of gain.
Backgrounding is a variation of preconditioning in which recently weaned calves are grown to heavier weights, usually in a smaller feedlot. The principal objective is to prepare these cattle to adjust to a high-energy finishing ration in a feedlot with minimal problems. This is achieved by feeding the calves a growth diet that yields rapid, efficient body weight gains without fattening. The spectrum of diseases seen in backgrounding operations during the first 45 days after arrival of the calves depends on whether the calves were preimmunized, preconditioned, or obtained from several different sources with no preconditioning. Infectious diseases of the respiratory tract (eg, BRD) and of the digestive tract (coccidiosis) account for most of the losses.
Recently arrived cattle of unknown backgrounds (eg, those from auction markets) require extra surveillance and care. After a 24-hr rest, these cattle should be vaccinated and some need to be castrated, dehorned, and treated for internal and external parasites. Nonpreconditioned, stressed cattle of unknown backgrounds should be watched closely for signs of BRD for ≥3 wk after arrival. On their starter ration, the cattle are limit-fed good-quality roughage along with a quantity of a highly palatable, nutrient-dense concentrate ration. They are checked carefully at least twice daily for evidence of illness, and sick cattle are identified and treated. Once the animals are determined to be healthy and the common infectious diseases are not a problem, they can be moved up to finishing diets.
Vaccination against certain respiratory diseases at 24 hr after arrival is standard practice for most feedlot and backgrounding operations. Vaccination should be limited to those products that actually reduce losses resulting from respiratory disease. The use of metaphylactic antimicrobials against respiratory disease may be necessary in high-risk, nonpreconditioned calves. Numerous studies show a financial benefit to using metaphylactic antibiotics on high-risk calves, because BRD morbidity and mortality can be greatly reduced.
Regardless of the system used, soon after arrival the cattle should be weighed, examined for evidence of illness, and treated if necessary. Some feedlots administer antimicrobials to all calves considered to be at high risk of acute respiratory disease. If the illness appears different from the usual case of respiratory disease, diagnosis by a veterinarian should be sought at the earliest possible time. Close examination and surveillance are desirable for groups of cattle with a history of unusual stress. The youngest and smallest cattle often need special attention, and it may be necessary to separate them from older cattle. A reliable history of vaccination, vitamin injections, implants, and anthelmintic administration would be useful but is usually not available. The major objective during the first few days is to avoid unnecessary stress and get most cattle consuming the starter ration. Depending on the condition of the cattle, it may be difficult during the first few days after arrival to easily distinguish sick cattle from healthy cattle, and careful clinical surveillance every few hours may be necessary. Observations at the time of feeding often reveal anorectic animals that should be pulled from the pen and examined.
Each animal must be identified immediately, preferably with a color-coded and numbered plastic ear tag that is easily visible from a distance. In many feedlots, each animal is not identified individually but instead receives a tag with a lot number (group) or pen number. Systems are now in place that individually identify animals with tags that can be read electronically from a distance of 8–10 in. Information maintained on individual animals through this technology may include performance, vaccination, and treatment history. These tags remain on the animal until slaughter, at which time the identification from the ear tag can be transferred to the overhead trolley system.
On arrival, some animals may be affected with acute disease but show no obvious clinical signs. Others may appear fatigued and gaunt but are not affected with clinical disease. Identifying animals with acute infectious disease that should be treated early to minimize mortality can be difficult. The body temperature of high-risk cattle (eg, unweaned calves, calves from auctions, or calves transported long distances over several days) is often measured at processing. Animals with a body temperature >104°F (40°C) may be treated with an antimicrobial. Treated animals may be tagged and noted in the individual animal database, or the total number of animals treated (total amount of drug administered) in a group or pen may be recorded.
The value of vaccinating feedlot cattle for common infectious diseases, particularly those of the respiratory tract, has been controversial since the vaccines were introduced. Nevertheless, a wide variety of vaccines are used in feedlot health programs.
Vaccines are available for the following diseases or infections of feedlot cattle: infectious bovine rhinotracheitis, pneumonic pasteurellosis, parainfluenza 3 virus infection, bovine respiratory syncytial virus infection, Histophilus somni disease complex, bovine viral diarrhea types 1 and 2, and clostridial disease. The vaccines available for clostridial diseases are highly effective. The number of clostridial antigens to be used (2- to 8-way) depends on local prevalence of clostridial diseases, including blackleg (Clostridium chauvoei), malignant edema (C septicum), bacillary hemoglobinuria (C novyi, type D [haemolyticum]), infectious hepatitis (C novyi, type B), tetanus (C tetani), and enterotoxemia (C perfringens types B, C, and D). Leptospirosis (Leptospira serovars Hardjo, Pomona, Grippotyphosa, Canicola, and Icterohaemorrhagiae) bacterins are also used in some situations.
A basic vaccination schedule for receiving calves should include a viral respiratory vaccine plus a clostridial vaccine. Additional vaccines should be included only if two criteria can be met: the disease is enough of a risk that prevention is necessary (eg, leptospirosis in some areas), and data are available to support the use of vaccines to prevent disease.
These surgical procedures are best performed well ahead of entry to the feedlot, but invariably there will be bulls and horned cattle offered for sale. When to castrate and dehorn these mismanaged cattle is quite controversial, with studies showing that performing surgery at initial processing 24 hr after arrival was superior to delaying these procedures.
Anthelmintics and insecticides are administered according to local conditions. Most incoming cattle will have been exposed to internal parasites, and appropriate deworming methods should be implemented. Young cattle raised on small farms in which the stocking rate on pasture is high may harbor helminths. Young cattle may also be affected by chronic verminous pneumonia caused by Dictyocaulus viviparus. Most young cattle will be infected with coccidia, and having an appropriate anticoccidial agent in the feed is necessary.
Growth-promoting agents (see Growth Promotants and Production Enhancers) increase growth rate of animals without being used themselves to provide nutrients for growth. They are generally administered in small amounts—often via implants or in feed—to alter metabolism so the animal increases body tissues and grows more rapidly. They include antibacterials, antimicrobials, steroids (eg, estrogens, androgens), and ionophores. They promote changes in composition, conformation, mature weight, or efficiency of growth, along with changes in the rate of live weight gain.