Foal Vaccination Strategies

A foal's protection against infectious diseases begins before birth. Vaccinating a pregnant mare four to six weeks prior to foaling helps her pass critical maternal antibodies on to her foal within the first 12-24 hours of his life. These maternal antibodies provide future immune protection to the foal, but they can also interfere with or inhibit his ability to respond to vaccinations. Specific antibody levels decline at various times during the first six months, so the owner and veterinarian need to establish a timeline for administering the various vaccinations. Foals born to unvaccinated mares generally need to be vaccinated earlier because they do not have the same level of antibody protection.

The American Association of Equine Practitioners has developed guidelines for foal vaccinations that include core and risk-based vaccines. (For specific vaccine dose recommendations, see Core vaccines have been proven effective and safe; therefore, they pose low enough risk and high enough benefit to be recommended for all foals. The core vaccines include those designed to protect against tetanus, Eastern/Western equine encephalitis (EEE/WEE), rabies, and West Nile virus (WNV).

The tetanus vaccination has been proven very effective in protecting foals from a disease that can often be fatal. Foals of vaccinated mares should receive their first of three tetanus vaccines at 4-6 months, whereas foals of unvaccinated mares should begin their three-dose series at 1-4 months.

Eastern and Western equine encephalomyelitis are fatal diseases caused by mosquito-borne viruses. Foals born to vaccinated mares should get their first EEE/WEE vaccine at 4-6 months, although those born in the southeastern United States and other areas where mosquito vectors are present year-round should have their initial dose at 3 months. Foals born to unvaccinated mares should have an initial dose at 3-4 months.

Rabies is a significant public health concern because of its high mortality rate in all species. Fortunately, rabies vaccines available for horses produce an excellent immune response and, therefore, protect horses well. Foals of vaccinated mares should have their initial dose at 6 months. A foal from an unvaccinated mare should have no maternal antibody interference; thus, a single rabies vaccine at 3-4 months should provide lasting protection.

West Nile virus, another mosquito-borne virus, is present across most of the country. The WNV vaccine is available in three licensed and approved forms: inactivated whole virus, modified-live chimera, and recombinant vector. See for various dose recommendations, remembering to begin WNV vaccination earlier in foals that are born during the mosquito season.

In addition to the AAEP's core vaccination recommendations, risk-based vaccinations apply to individual populations and geographic regions. These include products designed to protect against anthrax, botulism, equine herpesvirus, equine viral arteritis, equine influenza, Potomac horse fever, and strangles.

Veterinarians might recommend vaccinating against anthrax, for example, a serious disease caused by soil-borne bacteria that grazing horses encounter in areas with alkaline soil conditions (see And botulism is an important disease to vaccinate against in Kentucky and in the Mid-Atlantic seaboard states. On the other hand, foals appear to have a low risk of contracting Potomac horse fever.

The remaining risk-based vaccinations are recommended based on the foal's exposure to other horses. A variety of equine herpesvirus vaccines are available and should be given at 4-6 months to all foals that will not be raised in isolated herds. Veterinarians often give colts (that might later be used for breeding) the equine viral arteritis vaccine. The equine influenza vaccine should not be given before a foal (of a vaccinated mare) is 6 months old due to the lasting presence of maternal antibodies. Strangles vaccines are available in a modified-live form and as a killed vaccine. Veterinarians do not recommend vaccinating foals during a strangles outbreak but, rather, only vaccinating if a foal might potentially be exposed to Streptococcus equi bacteria.

Horse owners are encouraged to consult their veterinarians for foal vaccination protocols in their specific geographic regions and populations.

About the Author

Jeffrey Cook, DVM

Jeffrey Cook, DVM, is an ambulatory veterinarian with Rood and Riddle Equine Hospital in Lexington, Ky.

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