Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Meningococcal disease wikipedia , lookup
Creutzfeldt–Jakob disease wikipedia , lookup
Middle East respiratory syndrome wikipedia , lookup
Bioterrorism wikipedia , lookup
Chagas disease wikipedia , lookup
Schistosomiasis wikipedia , lookup
Bovine spongiform encephalopathy wikipedia , lookup
Brucellosis wikipedia , lookup
Eradication of infectious diseases wikipedia , lookup
ALABAMA COOPERATIVE EXTENSION SERVICE, AUBURN UNIVERSITY, ALABAMA 36849-5612 Diagnosing Disease Problems In Livestock James G. Floyd, Jr. Extension Veterinarian W hat killed her, Doc?'' is a question farmers often ask veterinarians. It is not unusual for livestock producers to encounter disease and death in their animals and herds. Sometimes death losses occur suddenly and unexpectedly. Howeyer, diseases such as mastitis in dairy cows, chronic pneumonia in stocker calves, or diarrhea in piglets may cause economically important production losses without sudden death. Often, diseases like some pneumonias in finishing hogs are caused by more than one factor. In these cases, the solution to the problem lies not just with finding the particular microbe (virus, bacteria, or mycoplasma) that caused the disease. Identifying the other conditions that may have made the pigs more susceptible to the disease in the first place is equally important. The challenge is finding a solution that is both practical and cost-effective. 11 What Is A Disease? The most useful definition of disease in livestock is stated in terms of productivity: Disease = Production Goals - Actual Production Consider this example: your production goal is to market hogs in 170 days or less, but your actual number of days to market is 190. By definition, your swine farm is suffering from "disease:' This disease may not be caused by a single factor, such as an infection. It could be the result of a particular type of pneumonia in the finishing barn combined with less-thanadequate nutrition or poor genetics for fast, lean growth. To define disease in terms of production goals, a producer must document actual production. Keeping accurate and current records is essential to this process. For example, in a dairy operation with mastitis problems, the producer needs information about milk production and somatic cell count to determine the effect of the disease on production. Without good production records, such as those available from the Dairy Herd Improvement Association (DHIA), the problem quickly becomes a guessing game. Losses from disease or death should not be accepted as a natural part of a livestock operation. Resources are available to help determine the cause or causes of disease and the appropriate action to prevent further losses. The producer's two main resources are a practicing veterinarian and the State Veterinary Diagnostic Laboratory. Used together, they can become valuable assets for any livestock operation. The Veterinarian As A Resource The best source of information on livestock health and disease is the practicing veterinarian. He or she is the local professional best qualified to offer an unbiased opinion about livestock health and how to maintain it. Establish a good veterinarian-client relationship with a veterinarian who is knowledgeable about your type of livestock and who will be able to work with you to solve any problems that may arise. A veterinarian can assist a livestock owner by designing a good preventive medicine program that minimizes the effects of disease on production. With a beef herd, for example, this may involve designing a good vaccination and parasite-control program, evaluating bulls for breeding soundness before the breeding season, and checking cows for pregnancy after the breeding season. The veterinarian can also help keep a herd free from diseases of regulatory importance, such as by vaccinating replacement heifers for brucellosis. If you work with a veterinarian on your herd's health-maintenance program, he or she will also be available to help in cases of disease outbreak. A good veterinarian-client relationship will allow the veterinarian to have a head start on helping you. In addition, such a relationship is necessary for the veterinarian to legally prescribe and use certain drugs on your farm. A veterinarian is also an invaluable resource in working with the veterinary diagnostic laboratory on CIRCULAR ANR-717 any problems your herd may be having. For an accurate diagnosis, it may be necessary to send samples from animals on your farm to the lab for testing. Only a veterinary professional can interpret the test results effectively. All the available medical technology used by laboratories is useless to a livestock owner unless the results can be translated into a plan of action or treatment for the farm. Knowledge of your farm, its animals, and your production system is an essential part of your veterinarian's ability to help solve disease problems. The Veterinary Diagnostic Laboratory As A Resource There are various veterinary diagnostic laboratories that can serve the livestock producer. The State Veterinary Diagnostic Laboratory offers a variety of services. Some private laboratories are also available throughout the country. Work with your veterinarian to use the diagnostic services available in your area. A written history of the problem must accompany any animals, tissues, or samples submitted to the diagnostic laboratory. This will aid the laboratory diagnostician in piecing together different parts of the puzzle. The history often determines the type of tests required. Therefore, a good history is essential for reaching a good diagnosis. Post-mortem examination ("necropsy" or "autopsy"). Particularly with death losses in livestock, a dead animal offers an important diagnostic opportunity. In some cases, several post-mortem examinations may be needed to establish a good diagnosis. Your veterinarian can work with you on submitting the appropriate samples. There is no guarantee that a necropsy will always provide a definitive answer to a problem. However, there is a 100-percent chance that the laboratory will not come up with an answer if the dead animal is not necropsied. An important part of any necropsy is the examination of the animal's body and organs, which is sometimes called "gross pathology:' Some diseases produce characteristic changes in certain organs. For example, blackleg in calves, caused by a Qostridium bacterium, can be rapidly fatal, causing characteristic discoloration in the muscles and gas formation under the skin. Usually the veterinarian will not rely on gross pathology alone to make a diagnosis. The veterinarian will submit samples of various tissues to the laboratory for further testing. This will invariably include histopathology, the microscopic examination of preserved tissues by a pathologist The pathologist will examine thinly sliced and stained tissue sections for microscopic changes that will help point toward a diagnosis. If your veterinarian is not available, you may deliver a dead or sick animal to the State Veterinary Diagnostic Laboratory. Be sure to take a good history of the problem and ask that a report of the laboratory results be sent to your veterinarian. When a post-mortem examination is conducted, it is important that the animals be as fresh as possible. As more time elapses after death, the post-mortem exam becomes less effective in establishing a cause of death. The bodies of small animals, such as piglets, should be put on ice for transport to the laboratory. In some cases it may be necessary to euthanize, or humanely put to sleep, a live representative animal from a herd experiencing a disease problem. This will help to ensure that the animal's tissues are fresh. In addition, a post-mortem examination on an animal that has just become ill and has not been treated for disease is often needed. This is important in cases of infections, when the laboratory will try to grow (''culture" J and isolate the organism causing the disease and determine which antibiotics will be most effective in treating other animals. If the animal has been treated, isolating the agent causing the infection will be more difficult. Your veterinarian can work with you to obtain the proper samples for submission to the laboratory. For example, in cases of abortions in cattle, the aborted fetus alone is not enough. You also need to submit samples of the fetal membranes, or placenta. Your veterinarian may recommend collecting blood samples from several animals in the herd, some affected and some unaffecteed, taken at intervals of 2 to 3 weeks, to provide all the pieces of the puzzle. The failure to include all of these may greatly decrease your chances of success. Perhaps this is why few cases of abortion in cattle, perhaps less than 10 to 20 percent, are definitively diagnosed. Microbiology. Microbial organisms, such as bacteria, viruses, fungi, or mycoplasmas, are often the infectious agents that cause disease in livestock. The veterinary diagnostic laboratory can take various samples from sick or dead animals and attempt to grow the organism on a culture medium. In some cases, the laboratory can also determine which drugs the organism will be susceptible to by conducting a sensitivity test. Samples for culture and sensitivity-testing can be taken during the necropsy from organs such as the lungs or intestines or from swabs from live animals. Toxicology. When poisoning is suspected, your veterinarian can submit samples of the stomach contents for analysis. Other samples, such as the liver, kidney, and brain, may also be examined for the evidence of poisonous substances. If a certain feedstuff is suspected as a source of poisoning, it may also be tested. These tests are sometimes quite difficult and expensive to conduct, and the laboratory may test only for the poisons that are most likely based on the history submitted with the sample. This is another reason for giving as accurate a history of the animal and the herd as possible. Blood Tests. Perhaps no other diagnostic area is more misunderstood than "blood tests:' Blood from animals can be used to test for many things, including: • Concentrations of certain chemicals in organs such as the liver. • The presence of toxic substances such as nitrate. • The presence of bacteria. • The relative numbers of various types of red and white blood cells, also known as a "complete blood count:' • Concentrations of antibodies to various infectious agents, also known as serology. Serology is often used to determine whether an animal has been exposed to an infectious agent, such as certain viruses or bacteria. If an animal is exposed to such a microbe, the animal may produce antibodies against it. The concentration of antibodies is often called the "titer:' The presence of a high titer in the serum, the liquid portion of the blood, may suggest that the animal was recently exposed to the agent and may provide evidence that it was a cause of disease. It is important to remember that a titer indicates previous exposure to an organism, not necessarily that the animal is infected with the organism or that the organism was the cause of the disease. With some diseases, such as brucellosis (Bang's) in cattle or pseudorabies in swine, the mere presence of a titer demonstrates that the animal is infected with the organism. Previous vaccination against those diseases will also cause a titer to be present. Titers of anitbodies against these diseases are particularly important because they are regulated by state and federal laws, and, in cases of positive titers, the government may require the herd to be quarantined or individual animals destroyed. With most diseases, interpreting serology reports is difficult and requires careful professional judgement. For example, routine vaccinations for infectious agents, such as leptospirosis in cattle, will cause an increase in the leptospirosis titer in the blood. For a serological analysis, it is best to submit samples from several animals, including some that did not show signs of disease. The concentrations of antibodies in these different animals may help to establish a diagnosis. Submit blood samples from these animals as soon as possible after the disease outbreak (the "acute'' sample) and then repeat the samples from the same animals 2 to 3 weeks later (the "convalescent" sample). If the convalescent titer is significantly higher than the acute titer, there is evidence that the infectious agent caused the condition. In any case, serology is frequently difficult to interpret, especially when it is the only test being used to diagnose disease. Serology is usually most helpful in conjunction with other diagnostic methods, providing an important part of the whole picture. Other 'Thsts. Many other diagnostic tests can be run, such as hormone concentrations in blood, fluorescent antibody (FA) tests for antibodies in tissues, and fecal flotation tests for the presence of worm eggs or larvae in the manure. As with other diagnostic tests, the veterinarian and the diagnostic laboratory should work together to submit the appropriate samples for testing. When the testing is complete, the veterinarian is responsible for interpreting the results and providing suggestions for solving the underlying problem on the farm. Review Diagnosis of disease in livestock can be difficult, but by using available professional resources you will have a better chance of diagnosing and solving the disease problem. Your practicing veterinarian and a competent veterinary diagnostic laboratory, working together, are indispensable assets. Both stand ready to help when you are faced with disease problems. CIRCULAR ANR-717 E The .6.1Aiabama i7Cooperative Extension Service AUBURN UNIVERSITY For more information, call your county Extension office. look in your telephone directory under your county's name to find the number. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension Service, Auburn University, Ann E. Thompson, Director, offers educational programs and materials to all people without regard to race, color, national origin, sex, age, or handicap and is an equal opportunity employer. UPS, 10M11, 12:92, ANR-717