Choose Vaccinations Suited to Your Horse

Horse people seem to fall into two main groups when it comes to vaccines: Those who give everything they possibly can and those who avoid everything but the most basic, fearing reactions, immune-system problems, and over vaccination. It’s concerns us that there’s so much misinformation out there. Download this entire article as a PDF here: vaccine article

Horses that travel are at the highest risk.


First, compared to the diseases they protect against, vaccines are safe. And that includes the major fear most people discuss—stress to the immune system. However, most vaccines don’t even come close to duplicating the immune-system stress caused by an actual infection. Think of the difference between normal reactions to getting a flu shot and actually having the flu. There’s no comparison.

Some folks worry about the inclusion of potentially toxic minerals in the vaccine preservatives (i.e. thimerosal) or the aluminum hydroxide adjuvants. These concerns are greatly exaggerated. Preservatives and adjuvants have been used for over 70 years. An adjuvant stimulates the body’s response to the vaccine, decreasing how much actual vaccine must be injected.

However, preservatives and adjuvants may explain the tiny percentage of horses that have a severe, reaction (anaphylaxis). This is why we advise horse owners not to attempt vaccines on their own, unless they’re certain there won’t be a reaction, such as you’re giving a horse the exact same vaccine as in previous years and he’s never had a reaction, lessening the risk.

Always ask the veterinarian for the vaccine vial label, if possible, and paste it into your horse’s health-care records. If not possible, get the name of the vaccine, the manufacturer and the vaccine’s lot number. (We ask for this information anyway for our horses, as it’s wise to have it on record.) If your horse does have a vaccination, avoid this brand in the future.


There are several ways to look at over vaccination concerns. One argument is that humans complete their vaccination series as babies and aren’t vaccinated again, except for tetanus and flu.

There are two problems with drawing direct comparisons. First, most equine vaccines contain killed organisms. This type of vaccine preparation leads to a relatively weak and short-lived antibody response and doesn’t stimulate the cell-mediated end of the immune response.

Second, even for vaccines that could reasonably be expected to last longer than one year (rabies, tetanus), no one has proven it. Titers are a good way to measure residual immunity from killed vaccines, but we don’t always know what titer is required for protection.

We consider two concerns about over-vaccination to be valid:

1) Vaccinating with an ineffective vaccine, and

2) Vaccinating without need.

Exposure risk must be taken into consideration, too. Horses on closed farms with no horse traffic in/out of the farm are at low risk for exposure to respiratory viruses or strangles, so there’s no reason to give those shots. (See sidebar.) See vaccines chart.


The American Association of Equine Practitioners (AAEP) recommends what they call the “core” vaccines, which cover serious illnesses to which virtually all horses have a risk of exposure. Some may even be required by law in some areas. All horses should receive these core vaccines:

Rabies. All horses are at risk for rabies. Horses are curious and a sick, rabid raccoon or skunk wandering in the pasture is likely to be nosed. A small bite may not even be noticeable but could cause rabies. Rabies is virtually 100% fatal. Even if your horse is never turned out, one rabid bat on the property is enough to cause quarantine for unvaccinated horses.

Rabies is a zoonotic disease, meaning your horse could infect you. A playful nip by a horse incubating rabies could lead to multiple vaccines for anyone exposed.

EEE and WEE. Eastern and Western equine encephalomyelitis are mosquito-borne diseases and can be fatal in horses. EEE tends to be deadlier. Despite the designations, both EEE and WEE occur throughout the U.S.

Both also tend to be “endemic,” meaning they always exist. On years when mosquito populations bloom and there are plenty of bird hosts around, we’ll see clinical cases of these viruses. These diseases are spread from bird to horse via mosquito, not horse to horse. People can also suffer from these viruses and even die. No matter how hard you try, your horse is likely to be exposed to mosquitoes.

The combined vaccine injection for EEE and WEE may also provide some protection against VEE (Venezuelan equine encephalomyelitis). VEE is a reportable foreign disease in the U.S., but it could rear its ugly head again. Specific vaccination for this disease isn’t suggested.

West Nile virus (WNV). WNV can be deadly. While survival rates are higher than EEE, many horses will have residual signs after the infection clears. This virus also comes to horses via birds and can infect people. As with the other encephalitis viruses, spread is almost 100% between mosquitoes biting birds, then horses.

Tetanus. Horses are sensitive to the toxin formed by the Clostridial bacteria. Clostridium tetani is in manure, soil and the intestinal tract of many animals. Horses become infected through puncture wounds, open cuts and even through the umbilicus in foals.

While horses can survive tetanus, the fatality rate is high. Nursing care and hospitalization can be extremely expensive and many horses never return to normal. Every horse is susceptible to getting small nicks and cuts that this bacteria could infect. Vaccination for this should be another absolute for all horses.


The AAEP’s list of risk-based vaccines muddy the waters considerably. There are equine vaccines for anthrax, botulism, equine herpes virus (rhinopneumonitis), equine viral arteritis, equine influenza, Potomac horse fever, Rotaviral diarrhea and strangles.

Whether these vaccines are necessary varies with the individual horse, geographical area and how often he travels.

Anthrax. If you live in an area where anthrax cases have been seen, especially with horses pastured on alkaline soils, your vet may suggest this vaccine.

Botulism. This can cause Shaker Foal syndrome and may be used routinely in breeding mares.

EHV or equine herpes. Aalso known as rhinopneumonitis, it causes serious uproar in the horse world when there’s a breakout.

EHV (aka the Rhinopneumonitis virus) exists in two forms. EVH-1 and EHV-4. EHV-1 is the most prevalent form. It can cause upper-respiratory disease (usually in animals under two years of age), abortion in pregnant mares, or neurological disease, which can be fatal.

Estimates are that from 60 to as many as 90% of adult horses are asymptomatic carriers of Herpes virus. These viruses are found in horses worldwide, with little variation between strains of virus around the world.

The vaccination is generally recommended for breeding mares to prevent abortion and in show horses for respiratory problems. Vaccine protection isn’t complete, and rhino hits all age groups.

Equine viral arteritis. This is mainly given to breeding stallions to prevent spread via semen. Your geldings and mares can skip this one!

Rotaviral diarrhea, Primarily used in breeding situations, as it’s given to pregnant mares to help their foals. Your gelding or barren mare can skip that one, too.

Equine influenza, Strangles or Strep equi, and Potomac horse fever (PHF) are more commonly recommended for horses out traveling and competing or in areas where the problems have been seen.

Flu tends to target horses under three, so it’s less of a concern for older horses. If you’re weighing rhino vs. flu, go with rhino due to its higher morbidity rate.

If a nearby barn has had outbreaks of strangles, you might want to consider that vaccine. Otherwise, most horses can skip that one.Plus, horses that have been naturally infected with the strangles bacterium, Streptococcus equi, have long lasting, if not lifelong, immunity, making vaccinations unnecessary.

The vaccine for PHF isn’t highly effective, so few vets suggest it.


Many people believe we over-vaccinate. While this may be the case, the data doesn’t exist to prove it.

Blood titers can be run to determine if the horse has antibody titers that show active protection, but we lack the research needed to link titer levels to protection levels. And, running a titer is likely more costly than a vaccine.

We recommend getting at least the no-excuse core vaccines for your horse. If your horse travels or you plan on breeding your mare, use our chart and talk with your veterinarian to decide on others.

As always, we aren’t keen on horse owners giving horses vaccines themselves because 1) You probably aren’t equipped to handle a reaction if it occurs and 2) For some horse owners, the annual vaccine visit is the only time you see your veterinarian, and it’s important to keep that connection active. You don’t want to call the vet with a colicky horse only to be told you’re not an active client and the vet is busy.

Contributing Veterinary Editor Deb M. Eldredge DVM

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