Although the question seems simple enough, there isn’t one answer for all horses. The answer depends on your horse’s:
- likelihood of exposure to disease
- duration of protective immunity from disease or vaccination
- your risk comfort level
We have produced general vaccination guidelines that can be viewed and/or downloaded from our website if you are looking for the simple answer. If you are interested in an explanation of what these recommendations “depend” on, keep reading!
Age: Young horses have lower levels of immunity than older animals because their immune system is naïve. Over time, as they are exposed either by vaccination or by experiencing disease, they become more immune to infections. Like all domestic animals, horses are born with NO immunity. They receive passive immunity from their dams by absorbing antibodies contained in colostrum. For this reason, we recommend boosting the immunity of the pregnant mare 6-8 weeks before foaling. Babies that have adequate transfer of antibodies from a vaccinated mare do not need to start their primary vaccination series until they are 8-10 months of age. If the dam was not vaccinated before foaling, these shots should start at as early as 3 months of age.
Likelihood of Exposure: Infectious diseases are caused by microorganisms that replicate in the horse’s body to produce disease. Communicable diseases are infectious diseases that spread from one horse to another. All of the diseases that we vaccinate for are infectious, but not all are communicable. Examples of infectious diseases that are not transferred from horse to horse (communicable) are Tetanus, Encephalomyelitis (Sleeping Sickness) and West Nile. All horses should be immunized against these diseases.
The most common communicable diseases of horses are Influenza, Equine Herpes (Rhino), and Strangles. Horses boarded in public stables, that recreate with other horses, and especially those that show, travel, or are in contact with horses that do travel extensively are at greatest risk. If you compete with your horses then consideration should be given to vaccinating for Influenza and Herpes. Boarding in a public stable also places your horse at risk of contracting a communicable disease.
The risk of exposure to some diseases is seasonal, since Encephalomyelitis and West Nile are carried from birds to horses and humans by mosquitoes. The species of mosquito most prevalent in early spring and summer is not very efficient in transferring the diseases, but another species that comes on late in the summer is. These diseases occur from July until we have a killing frost, usually around the first of October. We obviously want to have the highest level of protection to coincide with the period of greatest exposure, therefore we recommend West Nile booster shots between early April and mid-June.
Equine Herpes Virus or Rhinopneumonitis has several strains which produce different diseases. Equine Herpes Virus 1 (EHV1) causes abortion in mares, coital exanthema and neurologic herpes. EHV4 is primarily a respiratory disease in horses less than three years of age. Many, if not most, horses carry one or more strains of the herpes virus, which they may shed when under stress. The unborn foal is the most susceptible, so that is why we recommend vaccinating the mare several times during her pregnancy. At this time, there is no vaccine that is able to claim protection against the neurologic form of herpes.
Duration of Protection: The chart below illustrates the seasonal risk, duration of protection from vaccination, and our recommendation for vaccinating against the major diseases of the horse in our area.
Your Risk Comfort Level: These are general recommendations. There are other diseases for which we may recommend vaccinating under special circumstances. Our doctors and staff will be happy to discuss your horse’s needs to help you decide what vaccinations are appropriate for your situation and your level of comfort with your horse's risk factors.