A healthy start | TSLN.com

A healthy start

Heather Smith-Thomas

Vaccinating mama at just the right time will lay a solid foundation for her foal's future health. This simple act helps the mare develop antibody-rich colustrum. If the foal ingests an adequate amount of colostrum shortly after birth, the passive transfer of healthy antibodies occurs, according to Dr. Tia Nelson, veterinarian at Helena, Mont.

"It's best to vaccinate four weeks before foaling so the colostrum will have as many antibodies as possible," she says. Nelson said if the mare has had the rhino series during her pregnancy, that this is also the time to administer the final injection.

After that, the foal itself won't need to be vaccinated for several months, if it obtained adequate colostrum at birth (nursing an adequate amount within two or three hours of birth). "If you've planned ahead and vaccinated the mare during pregnancy, you don't need to vaccinate the foal until it's between four and six months of age, when the immunity from colostrum is waning. For mares that foal in April through June, for instance, we don't worry about vaccinating those foals until about weaning time, unless they become injured and we decide to give a tetanus vaccination," says Nelson.

"Most veterinarians don't recommend vaccinating foals before four months of age, since the maternal antibodies from the colostrum neutralize the vaccine. The exception we'd make is with tetanus. If the foal is vaccinated for tetanus soon after an injury or wound, this will give protection. We can use the tetanus toxoid, rather than the antitoxin, because the latter isn't as safe; the foal might get a serious reaction or Tyzzer's disease, from antitoxin. The foal will develop immunity quickly enough from the toxoid and we don't need to use the antitoxin," she says.

"Tetanus is also very responsive to penicillin. So if a foal gets injured, you can give an injection of penicillin at the same time you give the tetanus vaccination. The biggest concern is not seeing an injury or a tiny wound and not giving the vaccine soon enough," she says.

"We usually recommend starting the core foalhood vaccines (eastern and western sleeping sickness, tetanus and West Nile) at about four months, but wait until the foal is a few months older for rabies and influenza vaccination—and then yearly after that. The 4-way shots that most people use (eastern/western, tetanus and West Nile) should be boostered a few weeks later. After that it's just an annual booster," says Nelson.

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"The thing that's nice about our region, with a short mosquito season, is that we typically only have to vaccinate once a year (after the initial series in the foal), since these vaccines offer four to six months of immunity." If you live in a region with mosquito activity through most of the year, you'd need to vaccinate two or three times per year.

Carrie Hammer, state horse extension specialist, and director of the equine science program at North Dakota State University has two sets of recommendations for horsemen– one for those who are raising their own foals (and can vaccinate the mare ahead fo foaling), and one for those who are buying weanlings or yearlings. They need to know the vaccination history on those young horses, if possible, to know whether they've already been vaccinated or not.

"We recommend starting at about four to six months of age, or about weaning time­—unless the mare and foal are left together longer. I recommend the AAEP core vaccines. Whether or not the owner needs to vaccinate against influenza or rhino depends on the situation, whether it's a closed herd or has horses going and coming. If it's a barn where show horses or boarding horses are coming in and out, I recommend they start those vaccination series as well. Strangles is another contagious disease that some people might consider," says Hammer.

Some owners think that if they have a closed herd they don't have to sorry about vaccinating, but the mosquito-borne diseases (eastern/western sleeping sickness and West Nile) are everywhere, and tetanus is also a risk, along with rabies. "It doesn't matter where your horse lives, there is always some potential for these diseases," she says.

If rabid skunks or other animals wander through a pasture, foals are especially at risk because they are curious. They may be attracted to an animal that's acting strangely, and get bitten. "Skunks are a major carrier in our area," she says.

It is important to follow label directions on every vaccine, and give the booster doses at appropriate intervals. Adult horses that have already been vaccinated—having gone through the booster series as foals and receiving annual boosters thereafter—need only one shot to kick up the immunity. "Almost all vaccines, except rabies, are generally a three-dose series with the first one at four to six months, then a booster four to six weeks later and then the third dose at about 10 to 12 months of age," she says.

"Many horse owners incorrectly assume they can give just one injection and the foal will be ok. That first dose simply primes the immune system and doesn't confer immunity. It takes another dose for the immune system to recognize it and mount a good immunity. This is similar to puppy vaccinations and taking their puppies in multiple times for their shots," says Hammer.

"If they have a foal and know the dam was not vaccinated, or know the foal didn't get colostrum, the vaccination series can be started at three months of age. If the foal did get a lot of colostrum from the dam, however, early vaccines may not work," she says.

Thus the history is important. "This is something buyers may not think about when buying a foal at weaning time. They often ask about medical history in terms of whether it has been ill or injured, but don't always ask if it has been vaccinated or if the dam was vaccinated, or if it received good colostrum," says Hammer.

Timing, and when to start the vaccines, can sometimes be a hard decision. "We talk about vaccinating at four to six months, but doing it at the same time you pull the foals off the mares, when you can handle the foals and do something with them, may not be the best time to vaccinate. Research in cattle, swine and other animals shows that the immune system is suppressed by stress, such as during weaning. Recent research at the University of Kentucky showed the same thing happens with foals." Just like calves, it may be best to vaccinate foals ahead of their weaning stress, so they have a chance to build immunity before they are weaned.

"You don't always have this opportunity, however. And if you just bought the foal, you generally want to get it vaccinated as soon as possible, to have protection. If a foal has just been weaned, you want to get it vaccinated, said Hammer. She offers the example of a production sale, with the pair coming in together and the mare going out one door and the foal another. "This is all the more reason to make sure it gets booster shots, since the foal's immune system may be suppressed at the first vaccination," says Hammer.

If it's your own mare or group of mares, you might be able to vaccinate ahead of weaning, or utilize a weaning strategy that is less stressful for the foal–such as mare and foal in adjacent stalls, or fenceline weaning where they can be next to each other. The foal can't nurse but still has mama right there for security, until weaning is accomplished.

When vaccinating foals, make sure the foal is well restrained, use proper techniques, and follow label directions for the product being used. "If the owner is not sure about something, discuss it with the veterinarian. There are several types of vaccine and they come in different forms–inactivated, recombinant, or modified live. It can be confusing, when trying to decide on what to use, with all the different brands and combinations. The veterinarian can answer questions about the vaccines, and proper vaccination techniques, or tips on vaccinating a foal versus an adult horse," she says.

"Foals are a bit more likely to have adverse reactions to modified live vaccines than are adult horses, so it's good to be prepared and know what to watch for and how to handle those, and not get too concerned if it's just a mild reaction. It's always wise to have an antidote on hand in case of a more severe reaction," says Hammer.

Some horses react more adversely to certain antigens or adjuvants, and if you give a combination vaccine containing four or more antigens you wouldn't know which part caused the reaction. "Sometimes it's wise to not give everything all at once in a seven-way vaccine. When I work with owners whose horses react, we give the vaccinations separately until we figure out which one is the culprit and plan subsequent annual boosters accordingly. But with a foal, it will be the first time it's ever been vaccinated, and it may be wise to not give everything all at once," she says.

"The literature tells us, from a research standpoint, that it is better to give the vaccines singly and not all at the same time. But this isn't always possible. If you give one, wait a week, give another, wait a week, and so on, it may take six or seven weeks to give those first doses. In some instances you just about have to do it all at once, or split it into just two sessions. The research tells us that the antibody levels are different giving them all at once versus spread out, but physiologically it still gets to a protective level. On big ranches with dozens of foals to vaccinate, this is the only practical way, especially if the owner won't have hands on those foals again soon," says Hammer.

It's good for owners to learn as much as they can about the best way to vaccinate foals for best results, and ask questions. "Your own equine veterinarian will usually have the best advice, since he/she knows and understands your herd, how the horses are being managed and used, the diseases in your area, etc. Talking to your own veterinarian can give you more specific information, compared to general advice."

An example is anthrax. "This acutely fatal disease crops up periodically in our area, and can affect horses, but I encourage owners to talk to their own veterinarian. Some years it's an issue and some years it isn't, and the vaccine carries some risk for adverse reaction. This vaccine doesn't have specific guidelines in terms of vaccinating foals, and it is not recommended for pregnant mares. Even for adult horses, I would discuss this with a veterinarian, because it is a very specific vaccine for very specific situations," she says.