It’s November, a time when breeders concentrate on getting their broodmares in top health for foaling and breeding season and horsemen ship yearlings to trainers for breaking and introduction to race training. An important part of their preparations is to vaccinate those horses before they leave home.
Most vaccines are administered by injection into the muscle (intramuscular), but several vaccines are also available in intranasal form (up the nose), namely those that guard against respiratory disease. Flu-Avert (Merck) protects against influenza; Pinnacle (Zoetis) is for strangles. Both contain modified-live organisms. Traditional intramuscular vaccines contain killed organisms.
Calvenza (Boehringer-Ingleheim), which combats herpesvirus, is slightly different. It is a killed vaccine that can be used as a combination intramuscular and intranasal vaccine. The first two doses of Calvenza are administered intramuscularly, and the third dose can be either intramuscular or intranasal. All doses are given three to four weeks apart.
What’s the difference?
When deciding whether to use a traditional intramuscular vaccine or an intranasal vaccine, the horse owner has to look at his or her individual horse’s situation, said Dr. Robert Holland. Holland helped develop the first equine influenza intranasal vaccine in the late 1990s during his PhD studies at the University of Kentucky’s Gluck Equine Research Center. He is now a practicing veterinarian in Lexington, as well as a consultant, through his Holland Management Services, on vaccine development.
“Intranasal can be effective quicker if there is a problem, like an outbreak,” he said. “When we did the original work on the intranasal flu vaccine, within seven days those animals were protected when challenged. If you did that with a killed vaccine, you wouldn’t get that protective immunity until two or three weeks. So if you’re near an outbreak or you’re in a big show, sometimes people think intranasal first before killed.”
Holland explained that intranasal vaccines produce a different type of immunity than intramuscular vaccines. Intranasal vaccines produce a protective barrier in the mucous membranes of the nasal passages. Intramuscular vaccines create a systemic immunity that attacks the virus once it enters the body.
“If we can create protective immunity in the upper nasal passage area, we might be able to prevent them from getting sick to begin with, because they have the antibodies and cellular immunity up in their nasal passages,” he said.
For broader protection against influenza, a horseman can administer the intranasal vaccine first, followed in one month by the initial dose of intramuscular vaccine, and then give the intramuscular booster three to four weeks later. This will establish both mucosal and systemic immunity.
“I think a lot of people with younger animals go with killed [intramuscular] and intranasal as well, hoping to get a broader sense of immunity,” Holland said.
“Another thing that I see is with horses going into high-stress areas or a show or some other competition,” he continued. “They might not want to use an intramuscular shot right in the middle of it. Say a horse has to do a very strenuous dressage test and they’d rather go with intranasal than give a shot in the neck when the horse is really flexed.”
Unlike intramuscular vaccines, which often cause muscle soreness and malaise, intranasal vaccines have relatively minor side-effects — sneezing or coughing for a day or two — but less than one percent of horses are affected.
Broodmares and colostrum
A foal gets its first immunity through ingesting the mare’s colostrum, a yellowish first milk that is rich in antibodies. To fortify that colostrum with antibodies, the mare must be vaccinated four to six weeks before her foaling date to give her systemic immunity. Intranasal vaccines create localized immunity in the nasal passages, but not systemic immunity. To have antibodies passed to the foal, its mother must be vaccinated with an intramuscular vaccine.
Holland wrote his PhD thesis on the function of maternal antibodies, specifically how they can interfere with foal vaccination.
“If you’re using intranasal for a mare, you’re trying to protect the mare, not get it into the colostrum for the foal,” he said. “I also like getting the mare into the area where she’s going to foal at least six weeks before, so she can develop immunity for local pathogens before she foals.”
He added that a foal should not be vaccinated until it is at least six months old to assure that maternal antibodies transferred to it in colostrum do not attack and nullify the vaccine.
Besides the scientific differences in intramuscular and intranasal vaccines, Holland said the individual horse’s disposition sometimes is a deciding factor on which one to use. Some horses, like some children, hate needles. Other horses may hate having a vaccine squirted up the nose. He recommended discussing this with your veterinarian when deciding which version to use.
For horsemen who vaccinate their own horses, if they are housed in a location where possession of needles and injectable medications is a violation of the rules, the intranasal route is permitted.
Important caveat
Holland said it is very important not to administer intranasal vaccines in your barn at the same time you are vaccinating with intramuscular vaccines.
“When we give the modified-live intranasal vaccine for strangles, we always tell people not to give intramuscular shots at the same time, because if it gets into a muscle, it can create an abscess,” he said. “So we really don’t want people to do that. We give either intramuscular one day and intranasal another day, or we give the intramuscular to all the horses first, then we give the intranasal, so we don’t contaminate anything.”
New to the Paulick Report? Click here to sign up for our daily email newsletter to keep up on this and other stories happening in the Thoroughbred industry.
Copyright © 2019 Paulick Report.
