How Livestock Combat Disease

March 2007
Lochrane A. Gary - Hardee County Extension, Director/Livestock Agent

Animals may inherit immunity to disease or they may acquire this immunity. The power to resist disease can be acquired in two ways:

  1. As the result of successfully overcoming a natural infection.
  2. As a result of administration of a biological such as vaccine or bacterin.

The immunization of livestock dates from Pasteur's development of effective vaccines against anthrax and rabies. Immunization is invaluable in protecting against a variety of viral, bacterial and even parasitic diseases. The immunization method has been used with varying success for the control of many diseases and now is considered as basic to some branches of animal husbandry as good feeding and management. Research is constantly adding to the list of diseases that can be controlled by preventive immunization.

Vaccination is an important tool in protecting individual animals from contagious diseases such as hog cholera which occur year after year in the same areas. It is a more dramatic curb of epizootics, protecting both uninfected herds in a contaminated area and susceptible livestock in disease-free areas. Federal and state programs are often initiated to bring diseases under control through a combination of quarantine, vaccination in each new area of infection, and disposal of infected animals. A recent example of this in Florida has been the control of Bang's disease or bovine brucellosis.

Vaccination may produce active and continuing immunity to a disease. No vaccine, however, can provide 100 percent protection for all animals, because animals differ in their response to vaccination and the amount of resistance they develop. Proper vaccination usually provides an animal with enough protection to withstand exposure to a disease that would have been fatal without vaccination. Many vaccines expose animals to mild attacks by specific disease microorganisms, or the products of disease-producing microorganisms may be contained in the biological. This stimulates the animal's built-in system of defense against invading microorganisms. Antibodies are nature's way of fighting disease microorganisms. Therefore, when a microorganism enters the body, the animal's cells form antibodies to combat the invasive microorganism. Even after overcoming the mild infection caused by a vaccine, the animal's body continues to produce protective antibodies. Within one or two weeks, enough antibodies are present to fight off future attacks by the same microorganisms and active immunity is therefore established.

Antisera give passive immunity to disease microorganisms and toxins. This form of immunity is immediate but short-lived, usually lasting from 2 to 4 weeks. Protection is provided by the antibodies contained in an antiserum produced in another host. When the supply of antibodies is exhausted, protection ceases. Administration of an antiserum does not stimulate an animal's body to produce antibodies of its own. Currently, there are more than 200 types of veterinary biologicals used to fight animal diseases, and vaccines account for more than 90 percent of the biologicals produced in the United States. The remainder are products used in treatment or diagnosis of animal diseases. Some biologicals are sold for use only by veterinarians; however, many may be purchased and used by livestock producers.

All livestock producers are encouraged to develop a herd health program in conjunction with their veterinarian. An immunization program for diseases endemic to your area should be considered a part of that program.

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