Horse Illustrated Magazine

Read to learn about horse vaccination facts and fiction.

We may live in the 21st century with information literally at our fingertips, but myths and misconceptions still abound. When it comes to protecting your horse from disease, a routine vaccination program is vital. So why do horses die every year from diseases that they can easily be vaccinated against? Blame it on a few common misunderstandings.

To sort out fact from fiction, we turned to experts Lisa Kivett, DVM, DACVIM, whose Foundation Equine Clinic is based in Southern Pines, N.C., and Kenton Morgan, DVM, DACT, who helped revise the latest vaccination recommendations for the American Association of Equine Practitioners (AAEP) and who works in Equine Technical Services for Zoetis.

Popular Fiction

Unfortunately, some horse owners hold on to the following myths and misconceptions:

• My horse doesn’t go anywhere, so he isn’t exposed to disease.
• Skipping vaccinations for a year or two won’t hurt because immunity lasts a while.
• My horse is older and has been vaccinated all his life, so I can back off vaccinating now that he’s retired.
• Foals are protected if their mothers are vaccinated, so I’ll wait to vaccinate until he’s a yearling.
• My horse doesn’t live in a rural setting, so I’m not worried about rabies.
• Once a year is plenty for any vaccination.
• There are too many side effects associated with vaccinating.

Core vs. Risk-Based

The truth is there are a handful of diseases all horses should be vaccinated against. That’s because these diseases have high mortality rates and all horses are potentially exposed. Used properly, core vaccines are very effective at preventing these diseases:

• Eastern equineencephalomyelitis (EEE)
• Western equine encephalomyelitis (WEE)
• Rabies
• West Nile virus
• Tetanus

Depending on your region and your horse’s age and exposure, your veterinarian may also recommend one or more of the following risk-based vaccines:

• Equine influenza
• Equine herpes virus type 1 and 4
• Strangles
• Potomac fever
• Others from AAEP list

Evaluating Risk

Some horse owners think their animals can’t be exposed to disease if they don’t show or travel, but this isn’t true.

Consider encephalitis and West Nile, for example.

Pathogens for disease are always in the environment, and these particular viruses are maintained within different bird species. These bird populations serve as the “reservoir” for the viruses; some birds can host the viruses but not suffer negative effects of their presence.

If a mosquito takes a blood meal from a bird that has the virus circulating in its bloodstream, that virus can multiply or replicate within the mosquito. So now that mosquito can potentially give the virus to a horse when biting it.

“The risk is always out there because the virus hangs around in the bird populations,” says Morgan. “As with all of the viral encephalitic diseases, some years have higher disease prevalence than others, but the risk is always there for unvaccinated animals.”

What About Immunity?

It’s hard to know how long immunity from a vaccine lasts because it varies from horse to horse. Even a titer test measuring the level of antibodies to disease in the blood doesn’t tell the full tale.

“I’ve treated horses with encephalitis that had been vaccinated 14 to 16 months prior,” Kivett relates. “Titer levels in horses aren’t well understood, and while we can draw blood for a titer, we can’t tell you what level is actually going to protect your horse from this disease.”

Morgan notes that one of the most common mistakes horse owners make is not keeping current on vaccinations. Going two and three years between vaccinating can put the horse at serious risk if he is exposed to disease.

“Your local veterinarian is the best person to set up a vaccination program for your horse, so he remains properly immunized and disease risk is mitigated,” says Morgan.

Young and Old

A young foal receives immunity from his mother, assuming the mare was properly vaccinated and the foal received enough colostrum shortly after birth. But protection from maternal antibodies only lasts a matter of months, and if the mare wasn’t vaccinated, the foal’s vaccination program needs to start sooner rather than later.

“Young animals actually require additional booster vaccinations to get their optimal immune response,” notes Morgan. “The AAEP vaccination guidelines recommend that foals receive three doses of vaccine by the time they are 1 year of age. This is typically done by starting their vaccination program at approximately four to six months of age with two doses of vaccine at a four- to six-week interval, and then giving a third dose at approximately two to three months later.”

It’s important to realize that without boosters given at the proper intervals, the young horse isn’t completely protected.

Morgan points out that a common misconception is thinking that older horses are at lower risk of disease due to their age. He emphasizes that this is not true, even when horses have been vaccinated for years.

“Geriatric horses should be kept current on their vaccination schedules,” he notes. “If we let their vaccinations lapse, they become at risk for disease—whether old or young.”

“Older horses often have decreased immune function, and decreased immune response to vaccines. This makes them more susceptible to diseases, and more likely to have incomplete protection without regular vaccinations,” says Kivett. “It’s a common misconception that a horse may have had enough vaccines previously in his life to remain protected forever. This just isn’t true. It’s actually more important to routinely vaccinate older horses.”

Why Worry about Rabies?

Many horse owners routinely vaccinate their dogs and cats for rabies, but don’t think it’s necessary for horses.

“Horses do get rabies. All it takes is a bite from a rabid animal that actually may go unnoticed by the owner,” says Kivett.

“The problem is that a horse with rabies may initially just look like he has colic, choke, or another typical health concern,” she explains.

“A veterinarian may come to the farm, treat the horse (with the owner handling it, of course) and find out days later, after the horse gets sicker and dies, that it had rabies. At that point, the vet, owner and everyone else who has touched the horse is at risk for developing rabies, and will need to get post-exposure vaccines. In addition, if your horse isn’t current on rabies vaccination and develops a different neurologic condition, he will have to be isolated at a hospital with a limited list of people who can touch him. This results in more expense to you, and a reduced chance that the horse will get the treatment he needs.”

Timing is Everything

Vaccinating once a year is enough—right? Not necessarily.

Depending on where you live, mosquitoes may be present year-round. For example, in Gulf Coast states it is common to give horses booster vaccinations every six months for mosquito-borne viral encephalitic diseases—West Nile, EEE and WEE.

“If the mosquitoes are active, so are the diseases they carry, and keeping horses’ immunity high is important,” states Kivett.

“Your veterinarian is the best person to help you make these decisions,” advises Morgan. “He or she will know the optimal vaccination intervals for your area and your horses.”

Vaccinating at the right time of year is also important.

To ensure your horse has the most protection from mosquito-borne disease, you’ll want him to receive booster vaccinations approximately three to four weeks before mosquito activity is expected in your area. For horses living in areas where mosquitoes can be present any time of year, talk to your veterinarian about the most effective times to give boosters.

Some risk-based vaccinations (influenza is one) need to be given every six months, regardless of geographic area, because the protection from the vaccine simply doesn’t last a whole year.

Concern About Side Effects

There are always horse owners who choose not to vaccinate because they are concerned about possible side effects of vaccination. Kivett says that each year she sees a very small percentage (less than 1 percent) of horses that develop a mild fever the next day or have slight leg swelling.

“Very rarely one may have mild colic symptoms. These horses get better with a dose of flunixin [Banamine], we mark their chart, and try a different brand or combination the next time,” she notes. “These horses are still alive, and no worse for the wear, unlike the ones that get encephalitis.

“In my mind, this is an overwhelming benefit-over-risk decision,” Kivett continues. “That being said, I do know of a few horses that have more severe allergic-like reactions, or auto-immune diseases that prevent vaccination. Making the decision to avoid vaccination is a decision that should be made for an individual horse, and should only be made when that particular horse is more likely to become seriously ill from vaccination than from encephalitis.”

“I’ve watched horses die from encephalitis and West Nile; it’s honestly terrible,” she says. “They stagger around, lose their personality, head press to the point of injury, have grand mal seizures, collapse with no ability to get up, and some rage to the point that no one can get near enough to even euthanize them. It’s heartbreaking, and I’m tired of seeing it.

“Every horse owner I’ve met in this situation has immediately started vaccinating their other horses, and never missed one again,” Kivett continues. “They often become advocates for vaccination, reaching out to friends to explain how important it is to vaccinate.”

DIY or Call the Vet?

Because of the availability of vaccines online and at your neighborhood feed store, many owners vaccinate their horses themselves. While this isn’t necessarily a wrong choice, there’s a lot to be said for having your veterinarian out to vaccinate your horse.

“Having a relationship with your vet that includes yearly or twice-yearly preventive health visits ensures that the vet knows you, knows your horse, and is ready to respond when you really need them,” says Kivett.

Yes, you will pay a little more if the vet comes out to vaccinate your horse than if you do it yourself—but maybe not in the long run.

This is because you can rely on your veterinarian to properly handle and store the vaccines correctly, something you can’t always be sure of if you order online or buy at the feed store. Plus, should your horse have a negative reaction, the veterinarian already knows exactly what vaccine was administered and that it was given correctly.

CYNTHIA McFARLAND is an Ocala, Florida-based freelance writer, horse owner and avid trail rider. The author of nine books, her latest is The Horseman’s Guide to Tack and Equipment.

This article about horse vaccination fact and fiction originally appeared in the April 2018 issue of Horse Illustrated magazine. Click here to subscribe!

Further reading:

Adult Horse Vaccination Chart

The Science Behind Veterinarian-Administered Vaccines