Vaccinating Young Horses


Equine Vet
The years between weaning your foal and starting him under saddle at age three or four are important as they set the stage for his development into a happy, healthy adult horse. Establishing an appropriate vaccination routine with your veterinarian will give your horse a solid foundation during these important years.

Young Horses and Disease Risk
Much of the discussion around equine vaccines relates to contagious diseases that horses pick up at shows or in public boarding stables. It may seem that vaccinations are less important for young horses that aren’t yet traveling, but Dr. Cynthia MacKenzie, DVM, Sr. Equine Technical Services Veterinarian for Merck Animal Health, explains that this isn’t the case.

“Young horses are usually more susceptible to contagious diseases and in particular infectious respiratory diseases,” says MacKenzie. “Their immune systems are oftentimes not fully developed. As a foal, vaccines need to be given at the appropriate time to ensure that a solid immune foundation is built. From age one to four, the immune system further develops by exposure to different pathogens or diseases and by subsequent vaccine boosters.

“The American Association of Equine Practitioners Vaccination Guidelines is a very good reference to begin to understand the different diseases, risks, benefits, types of vaccines, number of doses, etc. in order to make an informed decision about vaccinations. This decision should also be made with the expertise and guidance of an equine veterinarian.”

The core vaccines recommended by the AAEP for horses of all ages are Tetanus, Eastern/Western Equine Encephalomyelitis, West Nile Virus, and Rabies. These diseases affect horses throughout North America and pose a serious risk to equine health. Fortunately, safe and effective vaccines are available, so getting your young horse protected is as easy as calling your vet.

Other vaccines are referred to as risk-based because they may not be appropriate for every horse. Some of the vaccinations that your vet may recommend include botulism, strangles, equine influenza and Potomac horse fever. Because not every horse is at risk for these diseases, it is important to discuss with your vet which ones are essential for your youngster.

A Positive Experience
These early vaccination experiences will shape the way your horse handles vet visits for the rest of his life, so make them as positive as possible.

“Veterinary visits should be handled in the same manner as any other early training experience,” says MacKenzie. “This generally requires patience, timing and a proper balance of positive and negative reinforcement. The first veterinary visit should allow a little more time and not be done while the horse is stressed or already anxious. Horses can be taught to accept veterinary procedures just like they can be taught to stand for the farrier or to be saddled.”

Don’t be afraid to ask for assistance from your trainer, barn manager or an experienced young-horse handler in preparing your horse for his early vet visits. A positive early experience will pay off in the long run and make your horse easier to handle during vet visits as an adult.

Reaction Risks
One final concern you may have when vaccinating your youngster is the risk of adverse reactions. An allergic reaction to a vaccine is a possibility, but it is a fairly uncommon occurrence, and one that can be managed with help from your vet.

“These types of allergies are rare in horses, and the horse is usually born with them,” says MacKenzie. “Therefore, initial vaccine administration can exhibit a reaction. Other allergies are acquired and horses can develop sensitivities to all parts of a vaccine, or just certain components with repeated exposure. An equine practitioner can provide guidance as to how to best vaccinate these horses and can present the risk/benefit analysis for that particular horse.

“Another consideration for all horses, but in particular young horses, is that the vaccination does not protect horses from developing disease,” adds MacKenzie. “For young horses, this may be due to their immature immune system where they are exposed to a disease prior to when their immune system can respond fully with a protective response. In some cases, the vaccines only minimize the duration and clinical signs of disease. In others, they keep the disease from reactivating in the horse, such as in the case with equine herpes virus infections. An equine veterinarian is the best resource for fully understanding the complexities of vaccination in all ages of horses.”


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