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This is the second part of our vaccine short-course. Cattle exposed to vaccines are not guaranteed to stay healthy. Even though the vaccine is right, the dose is right, and correct handling procedures were followed, the cattle may fail to respond to the vaccine and develop immunity. Let's stop right here and get some terms clear. Health is the state of the animal. Immunization includes vaccination and the response of the animal to develop immunity. Just because we vaccinate an animal does not mean the animal does its part and develops immunity. Likewise, immunity is not developed as soon as you pull the needle out. It may take several days for the animal to develop a solid immunity. Science tells us that even if everything is just right, only 85 to 95 percent of cattle respond to vaccination and develop immunity. In stressed cattle, potentially 60 percent or less may be able to respond to an on-arrival vaccination. Response to vaccination is a very individual thing, and a lot of factors are involved. Let's talk about a few: Nutrition. Energy, protein, macro- and micro-mineral nutrients, and water are all essential to maintenance of the condition we call "health." These must all be supplied in sufficient quantities and on a regular enough basis for the animal's immune system to develop and maintain immunity. Recently, the NAHMS program, an agency of USDA, surveyed forages and hay in production settings across the country, and found almost no situation where all the essential nutrients were all available. This is why we supplement. We know that adequate supplies of copper, zinc and selenium are essential for response to vaccines. Stress. This can be social, shipping, nutritional, weaning, weather, noise, etc. As we add additional stresses, response of the immune system to vaccination declines. The way we market and ship calves in this country could be compared to taking a town full of five-year-old children, loading them on the bus, not giving them anything to eat for 48 hours, hauling them halfway across the country, and then putting them in boarding school. Wonder how many of them would get sick? Prior exposure and incubating disease. With shipped-in cattle, we almost always have a subset of cattle that have been exposed previously and are incubating disease, have clinical disease or are in the recovery period. Incubation periods for IBR and BVD are considered to be around 2-4 and 5-10 days, respectively. So if calves are exposed at auction barns, collection points, or in transportation, they can potentially be in the latter stages of incubation on arrival at your place. Interaction with other products. If two or more products are introduced into the same location in tissue, one or both may be adversely affected. Also, where products are given subcutaneously or between muscle divisions, they can migrate as the animal moves or with gravity. For these reasons, a good rule of thumb is to keep injections separated by three or four finger widths. Also, some veterinarians believe that it is possible to overload the immune system with vaccine antigens so that poor response is gained to any of the products administered. If you think about it, we may give four types of viral antigens (IBR, BVD, PI3, BRSV), four to seven clostridial antigens (in the 4- or 7-way "blackleg"), one to four gram-negative bacterins (Pasteurella haemolytica, Pasteurella multocide, Hemophilus somnus, maybe even Salmonella), and maybe even a pink-eye (another gram-negative). That's a total of 16 antigens. Previous exposure to vaccines. Normally, this has a positive effect on response, and the animal can respond maximally, since it is already geared up to do so. This has been referred to as a booster or anamnestic response. Boosters should be given at proper intervals, so read the label. Toxins. Cattle may be exposed to environmental or feed borne toxins. A good example is aflatoxin sometimes found in some feedstuffs. Total ration levels of aflatoxin greater than 100 parts per billion can retard the response to vaccines. When we take all of the things that could go wrong, it is easy to understand that there is almost always a subset of a group of cattle that can't mount an immunological response to a vaccine. We often manage around this with either revaccination or booster dose or both. Revaccination is a second dose of the vaccine administered seven to 14 days after the initial dose. It is used to pick up those animals who didn't respond to the first vaccination. By this time we may have corrected stress, nutrition, exposure or other problems present at the primary vaccination. A booster can be considered as a second vaccines exposure which stimulates the animal to develop a higher quality of immunity (watch cattle for several hours following vaccination.) For animals who responded to the first dose of the vaccine, the revaccination may indeed produce a booster response. Article courtesy of Fort Dodge Animal Health. |
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