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"The ability of cattle to resist the many disease processes that they are exposed to is truly amazing. Yet, when several adverse factors combine, this resistance can be overcome, and result in a herd disaster that is just as amazing," says Utah Sate Extension Veterinarian Dr. Clell V. Bagley, in a paper titled "Disease Resistance in Cattle." In order to obtain disease resistance, Bagley recommends considering all aspects of a calf's life, including their natural ability to adapt, their immune system, and how vaccines affect their ability to resist disease. Adaptability A calf's body stores essential nutrients (water, energy, protein, minerals and vitamins) so normal functions continue in the event of a moderate period of deficiency or starvation. "The rumen microorganisms can digest a wide variety of materials, however a period of adaptation is required with feed changes to allow these rumen microbes to adjust," explains Bagley. "If this period is not provided, the calf's resistance may be decreased and disease may result." The same is true for fluctuation in the weather. "Cattle are able to adjust to great extremes over a few weeks' time. Yet one of the greatest stresses for cattle, and a major contributor of respiratory disease, is the wide temperature fluctuations that occur in a 24-hour period during spring and fall. These rapid changes tend to precipitate disease problems." Immune System The immune system of a calf can fight off many diseases, especially if the calf is carrying the antibody for that disease. However, antibody immunity is relative and depends on the level of exposure as well as other current stresses and general health. Bagley cautions that exposure to one strain of an organism may result in an immunity to that specific strain, but not to other strains of the same organisms. Vaccines To introduce particular antibodies in a calf's system, vaccines are used. "The effective immunization of calves is challenging," Dr. Louis J. Perino of West Texas A&M University told producers at a Cattlemen's College. "In trying to make vaccines and vaccines regimens fit into the marketing and production systems of the U.S. cattle industry, producers sometimes use vaccines at the wrong times, with too few doses, or with poor technique. We need to adjust our thinking and work with the biologically content features of the calf's immune system." Bagley says it is important to remember that there is a time delay involved for immunity to develop. "It takes the cow's body time to respond and build the antibodies. Cattle will seldom have any protection from vaccines until 10 to 14 days after vaccination. The handling of vaccines is an important aspect of the immunization process. Vaccines need to be stored and administered according to the manufacturer's instructions. "Special care must be taken with any modified live vaccine, either viral or bacterial, to prevent inactivation of the vaccine by exposure to temperature extremes, ultraviolet radiation, disinfectants, and so on," says Perino. An immunization management program and specific vaccine strategies should be developed with a veterinarian familiar with the operation, type of cattle and disease problems cattle typically experience. An immunization management program will help the overall health of the herd and improve survival rates in calves. |
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