Why vaccinate? In order to determine which vaccinations to administer, you must first consider the risk of disease, consequences of diseases, effectiveness of the vaccine, adverse reactions, and the cost of immunization verse cost of disease. Another consideration to keep in mind is that protection is not equal among individual horses and in various situations. Protection is not immediate; it takes time to become effective. Control and prevention are key; however, vaccinations are only one consideration and other precautions should be taken.

How does a vaccine work? When we give a horse an injection, an antigen is introduced into the body.  The body responds by producing antibodies to protect the horse from the antigen which was introduced by the vaccine.  That way when the horse is naturally exposed to the virus, the body has the antibodies to fight the disease.

Risk Factors & Prevention

What factors effect vaccination decisions? Various levels of exposure such as, traveling to shows, boarding facilities, and traveling across state lines plays hand in hand with increased exposure and risk. Movement of horses on and off facilities should be considered as it increases risk of exposure to all the horses involved, not just the ones being moved. When considering the condition of each horse, stress, parasites, nutrition, and sanitation are also factors that increase risk.

Environmental and managerial influences are great preventative measures. Having a manure management plan in place as well as a plan to reduce/eliminate standing water on site are two easy and effective ways to reduce disease risk. Managing each of these factors removes or at least reduces the breeding ground for mosquitoes and other unwanted parasites.

Core & Risk Base Vaccinations

There are two main categories of vaccinations: core and risk based. Core vaccinations are those considered to be annual regardless of the environment, travel situation, and animal condition. Core vaccinations include Eastern and Western encephalomyelitis, Tetanus, West Nile virus, and Rabies. Factors that largely determine which risk-based vaccinations are needed for a horse include geographical location, management practices, age, amount of travel and the horses use or purpose. Risk-based vaccinations include Rhinopneumonitis, Equine Influence, Botulism and Strangles.

 Core Vaccinations

  • Eastern and Western encephalomyelitis is a zoonotic disease, which circulates in nature between mosquitos and wild animals. Eastern encephalomyelitis is the most fatal when compared to other strands of encephalomyelitis, with a 90% fatality rate. Vaccinations should be given annually. Broodmares should be vaccinated four to six weeks prior to foaling, as similar with many vaccinations. This protects the mare and maximizes concentrations of immunoglobulins in colostrum. Antibodies are passed from the mare to the foal. In horses where we do not know their history or are unvaccinated, two doses four weeks apart should be given. Ideally, vaccinations should be given in the spring considering the seasonality of the disease, as vectors are mosquitos.


  • Tetanus is a fatal disease caused by a bacterium. It is not contagious but can remain present in the soil for an extended period of time. Tetanus often results from puncture wounds, lacerations, surgical incisions, umbilical in foals, or the reproductive tract postpartum. Vaccinations should be given annually (4-6 weeks pre-partum). In horses whom we do not know their history or are unvaccinated, two doses four weeks apart should be given. A booster should be given after injury or surgery.


  • West Nile virus is the leading cause of encephalitis in horses and humans in the United States, and it is a zoonotic disease. This virus is transmitted by mosquitos with a 33% fatality rate. Horses which recover still exhibit residual effects such as, gate abnormalities. Vaccinations should be given annually (4-6 weeks pre-partum). This vaccine should be given seasonally in the spring.


  • Rabies is a neurological, zoonotic disease from the bite of an infected animals such as, raccoon, skunk, fox and bats. Rabies is rare, but fatal in horses. There are a wide range of clinical signs including slobbering and aggression. This is an annual vaccination (4-6 weeks pre-partum or prior to breeding).

Aside from the core vaccines, risk-based vaccinations should be given on a case-by-case basis. When considering various vaccinations, it should be noted a separate injection is not required for each individual vaccination. Rather there are various options available where a single injection protects against multiple diseases. Collaboration with your veterinarian is always recommended to determine the best approach for your equine partner.