Debra Sellon, DVM, PhD, associate professor of equine medicine at Washington State University’s vet school, spoke about equine vaccination principles and strategies at the Western Performance Horse Forum held in Nampa, Idaho, on Feb. 15-17. She stressed two goals when considering immunization: 1) To prevent infectious disease; and 2) To comply with requirements for travel, competition, and breeding.

While vaccines are helpful in the prevention of infectious disease, an owner’s implementation of strategies to minimize exposure and to maximize a horse’s immune system, and be able to recognize signs of disease early to minimize exposure to others.

She recommends a “TROTS” approach:


  • Twenty-one- to 28-day isolation;
  • Reduce stress;
  • Observe and monitor for signs of disease;
  • Treat for parasites;
  • Sterilize and disinfect.

To adequately immunize, one must consider the disease being vaccinated against, the horse’s immune response to the disease, the technology of the vaccine, how it elicits an immune response, and horse and owner requirements.

Sellon reviewed basic immunology, stressing that of the two arms of immunity (humoral antibodies and cell-mediated immunity or CMI), a viral vaccine response is best if skewed toward CMI protection and production of immunoglobululin IgGb. She reviewed the concept of vaccinating for individual immunity against non-contagious diseases, such as equine encephalitis, West Nile virus, and tetanus, as well as rabies. She also emphasized the importance of immunizing a herd against equine herpesvirus-1 and -4, influenza, and strangles.

Strategies for different needs

Pregnancy can change a mare’s vaccination requirements. Sellon said pregnancy is, in a sense, like a foreign protein (antigen) eliciting some degree of immune suppression in