Karl Hoopes

Karl Hoopes

Spring is a typical time of year to vaccinate horses against disease. The American Association of Equine Practitioners has instituted a set of guidelines for equine vaccinations but a “standard” vaccination program does not exist.

Individual situations should be evaluated on the following criteria:

• Risk of disease (anticipated exposure, environment, age, breed, and use of horse)

• Consequences of the disease (mortality, zoonotic potential)

• Anticipated effectiveness of the vaccine

• Potential adverse reactions to a vaccine

• Cost of immunization vs. potential cost of the disease

As you consult with your local veterinarian, you will be able to decide when to vaccinate and what products to use.

The AAEP has listed five vaccines as “core vaccines.” These vaccines protect against diseases that are endemic in a region, that are potential public health concerns, highly infectious, or pose a risk of severe disease. These vaccines have demonstrated efficacy and safety. The core equine vaccinations include eastern encephalomyelitis, western encephalomyelitis, West Nile, tetanus, and rabies. Unvaccinated horses should receive a two-dose series with a six- to eight-week interval between doses. Begin vaccinating foals at 4 months of age. Previously vaccinated adult horses should be vaccinated annually. Pregnant mares should receive the vaccinations six to eight weeks before foaling to ensure that the mare’s colostrum will have antibodies.

Eastern/western encephalomyelitis and West Nile virus are spread by mosquitos. Vaccinations should be done at least a month before the anticipated onset of mosquito season. This allows the horse’s immune system enough time to mount a protective response.

Tetanus is caused by toxins in spore-forming bacteria found in feces and soil. Because horses are extremely sensitive to this toxin and it is abundant in our surrounding environment, it is an ever-present concern. Vaccination boosters should be administered to horses that receive a wound or undergo surgery more than six months after any previous booster.

Rabies is spread through the saliva of an infected animal. Although equine cases are very rare, rabies is endemic in every state except Hawaii. Due to the potential of spreading to humans, zoonosis, rabies is considered a core vaccine. It should be noted that in most states, rabies vaccination must be under the direct supervision of a veterinarian.

In addition to “core” vaccines, we have “risk-based” vaccines. These vaccines should be incorporated into a vaccination program after a risk analysis is performed by the owner and the veterinarian. The use of risk-based vaccines may vary depending on region, risk of exposure, use of the horse, and severity of the disease. Risk-based vaccines include equine herpesvirus, equine influenza, equine viral arteritis, leptospirosis, Potomac horse fever, rotaviral diarrhea, snake bite, strangles, anthrax and botulism. Equine herpesvirus, equine Influenza, and strangles are common causes of respiratory disease in horses. These diseases spread easily between horses at equine events. Some events require these risk-based vaccinations as part of biosecurity policies before horses are allowed to attend.

Equine vaccines as a whole are safe and offer a good source of protection. However, no vaccine is completely protective. Implementing good biosecurity measures will help prevent the spread of disease. Early recognition and treatment of any disease increase the likelihood of a positive outcome.

Karl Hoopes, DVM, is the equine specialist at Utah State University Extension and assistant professor in the USU School of Veterinary Medicine. Before joining the faculty at USU, Karl worked as a mixed-practice veterinarian. He can be reached at karl.hoopes@usu.edu.