BY HORSE Vaccination Guidelines

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General Horses (Risk Factor: Geographic Location)

Horses maintained on rural properties with little or no contact with other horses have minimal risk of coming in contact with these agents. However, if they do, they often exhibit severe signs of disease since their immune systems are relatively naive (little or no immunity).   It is recommended that horses exposed to minimal risk are vaccinated with the basic or core vaccines. It is also important to recognize that different disease agents have different geographic distributions. This can be related to;

horse in a field
  • • the ecology of the vector, e.g., Culiseta melanura, the mosquito vector of EEE, seems to be confined to some swamps and is probably related to the migration of birds from infected areas in the Southern USA to the same general summer ranges.
  • • Potomac horse fever is generally reported from Eastern Ontario. This may be related to the complex aquatic ecosystem associated with the insect vectors (caddisflies, damselflies, dragonflies, and stoneflies). Horse owners report very large hatches of these insects at certain times of the year in these areas.

Broodmares (Risk Factor: Pregnancy)

Pregnant mares are definitely at the greatest risk of being affected by an infectious agent such as bacteria and viruses. The agent can either kill the fetus in utero directly or cause hyperthermia, which can also result in abortion. In either case, the financial loss is tremendous.

foal and mare Some infectious agents, such as herpesvirus can lay dormant (latent) in horses until they are stressed by circumstances such as shipping. The virus becomes active again and results in virus shedding. Pregnant mares become infected and abortion storms can ensue.
It is for this reason, management practices, such as separation of all mares from the “in and out traffic” to the farm, are the number one tool in preventing abortions. The use of vaccines is a small part of the overall management strategy.
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Foals (Risk Factor: Age)

Passive immunity (protective immunoglobulins absorbed from the mare’s colostrum) provides virtually all of the foal’s antibody protection for the first 9-12 weeks of age. Foals begin to produce protective immunoglobulins (active immunity) immediately after birth when they are first exposed to antigens. However, a protective concentration of these immunoglobulins (active immunity) may not be reached until the foal is two months of age.

To maximize the foal’s protection to the common pathogens, mares should be vaccinated 4-6 weeks prior to foaling. Vaccination of the foal usually should not start until six months of age. Foal vaccination is delayed until six months of age when maternal antibody concentrations are waning and less likely to interfere with the foal’s ability to produce active immunity to vaccines. For tetanus (tetanus toxoid), Eastern equine encephalitis (EEE) and West Nile virus (WNv);

foal's head • Foals from non-vaccinated mares should receive their first vaccination between 3 and 4 months of age; the second between 4 and 5 months of age; a third between 5 and 6 months of age.

• Foals from vaccinated mares should receive their first vaccination at 6 months of age, followed by boosters at 4 to 6-week intervals, e.g., booster vaccinations at 7 and 8 to 9 months of age.

• Foals vaccinated with the live West Nile virus Flavivirus vaccine only require one vaccination at 5-6 months of age followed by a booster at 10-12 months of age prior to the next mosquito season
horse in a trailer

Traveling Horses (Risk Factor: In and Out Traffic)

Barns and stables where there is a lot of “in and out traffic” significantly increase the risk of exposure to the viral and bacterial agents.

It is recommended that mobile horses exposed to maximum risk – such as racehorses and show horses – are vaccinated for influenza, rhinopneumonitis (ie. Equine herpesvirus) and strangles.

Please note: This information provides guidelines only and should never replace information from your veterinarian.


Guidelines for Vaccination of Horses.  Guelph; Dr. Bob Wright (OMAFRA) and Dr. Dan Kenney (Ontario Veterinary College), 2004
Guidelines for The Vaccination of Horses. Lexington; AAEP, 2008

For more information, contact:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
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