One of the most confusing aspects of horse ownership can be sorting out annual vaccinations and deworming plans. There are so many different shots and deworming products available on the market today, how do you know what to use and when? The following simple explanations and charts should help shed some light on this confusing issue.
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In March of 2008, the American Association of Equine Practitioners (AAEP) revised its recommendations for vaccinating your horse. Vaccines have been divided into two types: (1) core vaccines, which are recommended for all horses based on risk of death to your horse if exposed to these viruses, and (2) vaccines that should be given based on risk of exposure to certain viruses. Several prominent factors that play a part in exposure risk include: how much your horse travels or is exposed to horses who have traveled, the likelihood that you may breed any of your mares, and the developing immune systems of young foals. (See the AAEP recommendation chart on the next page.)
Core vaccinations. "Core" vaccinations are the ones you don't want to skip. Risk of exposure to the viruses that make up the core group may not be very high, but the consequences of the infection could be death or permanent damage. In the case of rabies, there is also a very real risk the horse could transmit the disease to people working with him before anyone realizes the horse has rabies.
Non-core vaccinations. In evaluating whether to give non-core vaccinations, you should weigh risk of exposure when deciding. The rotavirus vaccine, for example, is only indicated for pregnant mares so that they can pass antibodies to their foals in the colostrum. Rotavirus only causes disease in young foals. Similarly, the botulism vaccine does not protect against the toxin strain typically found in adult horse cases of botulism, but does apply to the form that can develop in foals. Anthrax is only a threat in very specific areas of the country. For the other diseases, discuss your horse's risk of exposure with your own veterinarian.
Effectiveness. Vaccines are most effective if the antibodies are present in high levels (called titers) when the horse is exposed to the disease. This means you can get best protection by correct timing of vaccines for seasonal diseases. The encephalitis viruses are spread by mosquitos, so it doesn't make much sense to vaccinate for these diseases in the fall. A few weeks before start of mosquito season is best. If your horse is only around a lot of other horses in the summer, time your respiratory disease vaccinations to be given a few weeks before your most active riding season.
Pregnant mares & vaccines. Pregnant mares are a special consideration because the antibodies passed to foals in the mares' colostrum (first secretion from the mammary gland) are critical for supplying them with antibody protection until their own immune systems can get up to speed. Mares are typically boostered 3 to 4 weeks before their expected foaling date to achieve maximal levels in the colostrum.
Foals. Timing of vaccination for foals depends to some extent on the vaccine, so details should always be worked out with your veterinarian. In general, foals from dams that were boostered close to foaling may not require their first vaccines until around 6 months of age, whereas foals from unvaccinated dams will require vaccinations a little earlier. However, you want to be careful to schedule these first vaccines to be completed at least 2 weeks before the stress of weaning.
Outbreak. One area of much confusion is whether horses should be vaccinated if there is a disease outbreak under way. There are many considerations in these situations. Vaccines do not provide immediate protection. If the horse has had the vaccine or the natural disease before, it will take from 1 to 2 weeks for any response to the vaccine to occur. If the horse has not had a vaccine or exposure before, most vaccines require a two-shot series and you won't have full protection for at least 4 weeks. Also very important is whether the horse has already been exposed. If the outbreak has already hit and is running through the barn, there's very little chance the vaccine will be able to work fast enough to protect these exposed horses, and it might even make things worse by adding to the burden on the immune system. If the disease has been located in your vicinity but not actually at your barn, a combination of vaccination and isolating the horses may be the way to go. Infectious disease dynamics can be complicated. Always work out a plan with your veterinarian.