Stop the Spread

As travel for horses becomes more commonplace, so does the spread of diseases. Here's a look at the latest in vaccines.

When it comes to vaccinating the horses in your care, the dizzying array of options can be confusing. So we spoke with Dr. Jim Smith (DVM) at Hagyard, Davidson and McGee, in Lexington, Kentucky, who gives many talks and presentations to horsemen about vaccines and vaccination. To stay current with what’s being recommended, he confers with several people who work with and research vaccines, and he also relies on the AAEP (American Association of Equine Practitioners) vaccination guide, the AVMA (American Veterinary Medical Association) principles of vaccination, scientific papers, and personal experience.

“There is inadequate data to determine a single best protocol for vaccination/revaccination of horses,” says Smith. “The annual revaccination schedule found on many vaccine labels is based more on historical precedent and USDA regulations rather than on scientific data. Revaccination of horses that already have sufficient immunity does not add measurably to disease resistance, and may increase their risk of adverse post-vaccination events or reactions.” And to increase confusion, “Vaccination schedule recommendations and route of administration should be modified fairly frequently. I tell all my clients that what I tell them today will not be exactly what I will tell them next year,” he explains.


In preventing disease, the goal is to reduce exposure and enhance resistance. “Many management procedures are every bit as important as vaccinating—such as quarantining new or sick horses, vaccination requirements before a horse is introduced to a farm or stable, separation by age and use, proper management of sick horses, vector control, and general health programs (clean conditions, proper nutrition, deworming, dental and hoof care).

Sick horses do not respond well to vaccination,” says Smith. It is very important that any horse coming into the stable or farm be vaccinated (and at specified dates) before arrival to help insure that this horse won’t bring disease to the farm or stable.

“It’s a good idea to have written requirements before a horse comes into a stable or boarding facility. That record should be sent to the stable ahead of time. Another important thing, if you suspect a horse has an infectious, contagious disease, is to separate it from the others, as soon as possible.”

You also need a way to ensure that people handling an infected horse don’t inadvertently carry the disease to other horses they handle. Washing hands, using different feed/water facilities, stall cleaning tools, etc. can help prevent spread of disease to other horses in the barn. “These things are in some ways more important than the exact vaccination protocol,” Smith says.

“Vaccination needs to be tailored to the specific farm or stable operation, and depends on probability of exposure,” he adds. Different parts of the country (with different climates and risk factors), and different types (and uses) of horses may have different needs for vaccination. “There’s no absolute protection given by vaccine. Schedule of vaccination, from manufacturer’s recommendation versus clinical experience, may differ. Multi-valent vaccines (giving protection against more than one disease) may be just as effective as single vaccines. Right now a group in our practice is looking at every one of our vaccination requirements, and some recommendations will probably be changed in the near future,” says Smith.


“Intranasal vaccines (such as for influenza) for performance horses have certainly been shown to be the best (versus injected vaccines). This is one of the few vaccines that provides some protection after the first dose; most vaccines don’t trigger much immunity until after they are boostered,” says Smith. “On the other hand, the intranasal vaccine for strangles—while it may afford good protection—has produced some serious side effects. Strangles is one of those diseases I do not recommend vaccinating for except in the face of an outbreak. This is a vaccine you should use only if you have to; the intramuscular ones are not much good at all and the intranasal ones can be dangerous. If you use the intranasal strangles vaccine, do not do any other vaccinating at the same time. This is where people get in trouble. They have a little strangles vaccine on their hands after giving the intranasal product and vaccinate for something else (an injection) at another site, and the horse develops a strangles abscess,” he explains.

Fort Dodge’s Kevin Hankins, DVM, who worked eight years at the Kansas State University Medical Teaching Hospital, says the animal science unit there had a long, ongoing problem with strangles. The new vaccine helps solve it. “This vaccine is much safer than the older injectables (which were notorious for serious reactions like anaphylactic shock), and more effective. We found the intranasal vaccine not only provided good protection, but in severe outbreaks it reduces the severity of the disease if a horse does get it. When we started using the intranasal vaccine at the horse unit, the number of outbreaks were reduced, and when they did occur, the severity of the disease was very mild compared to what it had been in the past,” he says.


“Horses certainly should not be vaccinated immediately prior to competition. If the horse will compete tomorrow, do not vaccinate today. A lot of horses will have a fever for a few days, so you want to vaccinate a few days ahead of time. You need to schedule vaccinations as much as you can around performances or when they will be exposed to other horses,” Smith says. Give the vaccination when the horse can have some days off, so he won’t have to work hard when he feels lethargic, and so the body has a chance to mount a proper immune response.

Reactions such as local muscle swelling, soreness, mild fever and lethargy are fairly common following vaccination. The AAEP guidelines recommend that horses not be vaccinated within two weeks before a show, performance event, shipping or any other stress. “Season of the year makes a difference, too, in when you should vaccinate. If you are in a region that may have eastern or western encephalomyelitis in the summer, the best time to vaccinate will be shortly before the mosquito season,” he says. When trying to figure out the optimum vaccination schedule for horses, talk with your veterinarian. He/she stays up to date on what’s happening with vaccines and can advise you on what’s best for the horses in your care.


Some new vaccines, like the recombinant vaccines for West Nile, seem to be very good. “I think all the vaccines for West Nile have proven very effective,” says Smith. “On the other hand, Potomac horse fever vaccines have not been shown to be very effective. Rabies is a little different. We do recommend using it. Though the number of rabies cases in horses is small, it’s life-threatening; every horse that gets rabies is going to die, and there is also risk for human exposure. If you’re unsure of a horse’s vaccination history, I would give two doses of rabies vaccine initially (not just one, as the manufacturer suggests).” Treat such situations as though the horse had never had any previous rabies vaccinations.

“West Nile virus vaccination is certainly recommended, with any of the available products, before the mosquito season in your area. I definitely think all performance horses need to be vaccinated for rhinopneumonitis as well,” he says. “Tetanus vaccine is probably the single best vaccine on the market. We don’t know how long immunity lasts, but a yearly booster is advisable. Many people use the combination vaccines that include tetanus. Tetanus is an immunogen that actually helps to stimulate the protection you get from the other vaccines, and that’s one reason it is included in those multi-valent vaccines. It helps those to do a better job of stimulating immunity. This is one reason to go ahead and use the multi-valent vaccine, but my problem with using them is that it’s not always an appropriate time of year to give all those vaccines together. I don’t use them very often, but they do give good protection,” he says.

“There are many good vaccines today, but management factors for preventing disease are important—and often overlooked. People expect vaccines to be perfect and give 100 percent protection. The only vaccine that actually comes close to that is tetanus. I have never seen or heard of a case of tetanus in a horse that was properly vaccinated. We have 60 veterinarians in our practice, so that covers a multitude of experience,” says Smith.


“You have to realize, when giving a multi-valent product, you are getting in just one cc the vaccine for three to five different diseases. You might not be giving quite as much as you would in a single vaccine. There is no clear cut evidence that they do a poorer job, however,” says Smith. And, you certainly want to make sure that the entire dose is delivered, and not spill any or lose a drop, or have it seep back out of the injection site.

“To be most practical, and to make sure you have an accurate dosage, use a small syringe when giving a small injection. When giving a one cc dose, use a 3 cc syringe rather than a 10 or 12 cc syringe. Your accuracy in dosage will be better,” he says. He also recommends using a 1-1/2-inch needle (rather than a shorter one), to go deeply into the muscle. “I use a 22-gauge 1-1/2 inch needle, and I think that helps to prevent possible reactions. When a horse does react, it’s generally to the adjuvant rather than to the vaccine itself,” says Smith. Diseases come and go, as the outbreaks of WNV and Equine Herpes have shown us. It is always best to talk with your vet about the program in your barn to make sure you are covered with the most up-to-date vaccinations.






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