Vaccinations for Pregnant Mares

Vaccination strategy for a pregnant mare is different than vaccination strategy for a non-pregnant horse. When you vaccinate a pregnant mare, you're not just protecting her. You're also setting up the foal for protection through maternal antibodies. Newborn foals don't have their own immune system to speak of. They rely entirely on antibodies from the mare's colostrum for their first weeks of life. So vaccinating the mare properly before foaling makes the foal safer when it's born.

Not all vaccines are safe during pregnancy. Some vaccines are live virus or modified virus and shouldn't be given to pregnant animals. Some vaccines are safe throughout pregnancy. Some are best given during specific times of pregnancy. Getting this right protects the mare and sets up the foal for success.

The general rule is simple: most core vaccines that are inactivated or killed virus can be given during pregnancy. Live virus vaccines, modified live vaccines, and some others shouldn't be given to pregnant mares. Your vet will know which vaccines are safe and which aren't. But it's good to know the reasoning so you understand why certain vaccines are being recommended or avoided.

Timing of vaccination matters. Many vets recommend vaccinating the mare during the last month or six weeks of pregnancy, particularly for certain vaccines. Vaccinating at this time means the mare produces high levels of antibodies that she passes to the foal through colostrum. The foal gets that protection from the moment it starts nursing. This is called passive immunity, and it's crucial for a newborn foal.

This strategy of late-pregnancy vaccination has real consequences for foal survival. A foal born with strong maternal antibodies against tetanus, West Nile Virus, and equine encephalomyelitis has protection during the most vulnerable period of its life—the first few weeks when it can't yet mount its own immune response. A foal born without this protection faces real risk from diseases that are preventable. The mare's vaccination isn't just about her health. It's literally about giving the foal a fighting chance at the beginning of its life.

Let's say your mare is in the last month of pregnancy. Your vet might recommend vaccinating her against tetanus, Eastern Equine Encephalomyelitis (EEE), Western Equine Encephalomyelitis (WEE), West Nile Virus, and influenza. These are core vaccines for breeding mares. They're inactivated vaccines, meaning they're killed virus and safe for pregnant animals. When you vaccinate the mare with these, her immune system responds by producing antibodies to these diseases. These antibodies end up in her milk.

When the foal is born and nurses colostrum—that first, rich milk—it gets the mare's antibodies. These maternal antibodies provide temporary protection against these diseases. The protection is temporary because the foal's own immune system will eventually break down these maternal antibodies and replace them with its own. But for the critical first weeks and months of life, this maternal protection is valuable.

Vaccines that shouldn't be given to pregnant mares include live vaccines like some rhinopneumonitis vaccines, some equine herpesvirus vaccines, and rabies vaccine (in some formulations). You vaccinate the mare before she gets pregnant, or you wait until after foaling to vaccinate. You don't give live vaccines during pregnancy.

Some vaccines should be given at specific times. Rabies, for example—if the mare has never been vaccinated or her rabies vaccination is lapsed, your vet might recommend vaccinating her during pregnancy, but only certain rabies vaccines are safe for pregnant animals. Make sure your vet knows the mare is pregnant and chooses appropriately.

The timeline usually goes like this: Ideally, you vaccinate the mare before breeding, making sure she's up to date on everything. Once she's pregnant, you avoid any new vaccines. In the last month of pregnancy, you do a booster vaccination of certain vaccines—tetanus, EEE, WEE, West Nile, influenza—to maximize her antibody response and the protection passed to the foal. After foaling, you can vaccinate against whatever you didn't do while she was pregnant.

After the foal is born, it gets colostral antibodies. It has passive immunity, but this wanes. Starting around six months of age, the foal's own immune system becomes capable of responding to vaccines. Most foals start getting vaccinated around four to six months old, depending on the vaccination protocol.

Mare vaccination is a way to jumpstart the foal's protection. The foal gets protection earlier than it could develop its own immunity. This is particularly important for serious diseases like tetanus and West Nile Virus, where delaying protection could be risky.

Plan vaccination during pregnancy in advance. Before the mare even gets pregnant, know what your vaccination strategy is going to be. Talk to your vet about timing, about which vaccines are recommended, about the schedule.

Make sure the mare is up to date on all her vaccinations before breeding. You don't want to discover during pregnancy that she's overdue for something. If she's not current, get her caught up before breeding. Once she's pregnant, your options for catching up are limited.

Keep vaccination records. Know what the mare has been vaccinated against, when, what her booster schedule looks like. This information is important for planning and for making sure you're not double-vaccinating or missing anything.

Talk to your vet about your specific situation. If you're in an area with high West Nile Virus risk, that vaccine might be particularly important. If you're in an area where rabies is a concern, that becomes important. If respiratory viruses are common where you are, influenza vaccine might be especially valuable. Your vet can help tailor a vaccine plan for your location and situation.

Vaccinate during the pregnancy according to your vet's recommendation. Usually this means boosters of certain vaccines during the last month of pregnancy. Don't skip this thinking you'll vaccinate the mare after foaling. The timing during late pregnancy is specifically to maximize antibodies passed to the foal.

After the mare foals, you can vaccinate against anything you didn't do while pregnant. Getting her fully current postfoaling makes sure she's protected going forward. A mare that foals and is exposed to disease can get sick, and if she's nursing a foal, that complicates treatment and affects the foal too.

Planning your foal's vaccination schedule should start before birth. Know when you're going to start vaccinating the foal, what vaccines it will get, what the schedule looks like. Discuss this with your vet.

If a mare has a reaction to a vaccine while pregnant, you want to know what to expect and how to handle it. Most mares tolerate vaccines well, even during pregnancy. Some might have mild reactions—soreness at injection site, mild fever, temporary off-feed. These usually resolve without intervention. If a mare has a serious reaction to a vaccine during pregnancy, call your vet immediately.

If you vaccinate with a live vaccine accidentally during pregnancy, it's not necessarily a disaster, but it's not ideal. Call your vet and let them know what happened. They'll advise you on what to do. Sometimes nothing happens and the pregnancy continues normally. Sometimes it's a problem. Knowing that it happened lets your vet monitor the pregnancy more carefully if needed.

If a mare isn't vaccinated before pregnancy and you need to vaccinate her during pregnancy, you have limited options. Some vaccines are safe, some aren't. Your vet has to be careful about what gets used. This is why vaccinating before pregnancy is better than trying to catch up during pregnancy.

If a mare's vaccination record is incomplete and you don't know what she's been vaccinated against, you might need to assume she's not protected and act accordingly. You can't give vaccines at random if you don't know what she's already had. Your vet can help sort this out, but ideally you know your mare's history.

Some mares don't respond well to vaccines. They have underlying immune issues or just don't produce good antibody responses. If you vaccinate such a mare during pregnancy, the foal might not get as much maternal protection as you hoped. Testing the mare's antibody levels before breeding, if she's known to be a poor responder, might help you plan.

The foal gets maternal antibodies but these can interfere with the foal's own vaccination response. If you vaccinate a foal while it still has high maternal antibodies, the maternal antibodies might neutralize the vaccine, preventing the foal from developing its own immune response. This is why foal vaccination usually starts around four to six months when maternal antibodies have declined. Your vet will advise on appropriate timing.

Your vet is essential for vaccination planning. They know which vaccines are safe during pregnancy, which ones are recommended for your location, what timing is optimal. They have access to current recommendations from equine organizations. They can advise you specifically about your mare's vaccination history and any special situations.

If your mare has never been vaccinated or her history is unknown, your vet can assess her and recommend appropriate protocols. If the mare is older or has health concerns, your vet can adjust recommendations accordingly.

If the foal is born, your vet will advise on when to start vaccinating it and what vaccines to use. They'll consider the mare's vaccination status, the foal's health, environmental risk factors.

Some breeding facilities maintain vaccination protocols for their mares. If you're boarding a pregnant mare at a facility, they usually have set vaccination schedules they recommend. Coordinate with them to make sure it aligns with your vet's recommendations.

Before you breed, have a conversation with your vet about the vaccination plan. Don't wait until the mare is pregnant to think about it. Knowing in advance what vaccines the mare needs, when she'll get them, and why she's getting them at that particular time means you understand the reasoning. You're not just following instructions—you're part of a plan to protect both mare and foal. A good vet will explain their thinking and welcome questions. A mare that's been vaccinated with purpose has a foal that's protected by intention, not just chance.

Vaccinate the mare properly before and during pregnancy so the foal gets good maternal protection. This is a critical part of breeding management that sometimes gets overlooked because people focus on the foal itself. But the reality is that the mare's vaccination status before foaling directly determines what protection the foal has at birth.

Remember that vaccinating the pregnant mare late in pregnancy is about protecting the foal, not just the mare. The timing is strategic to maximize antibodies passed through colostrum. A mare vaccinated a month before foaling passes stronger antibodies to the foal than a mare vaccinated much earlier.

Know which vaccines are safe for pregnancy and which aren't. Ask your vet to explain why certain vaccines are being recommended or avoided. Understanding the reasoning helps you feel confident in the plan and helps you remember it if you breed again.

Keep records of everything your mare is vaccinated against so you know what protection exists and what might need updating after foaling. This becomes valuable history for future breedings.

Remember that maternal immunity doesn't last forever. The foal will need its own vaccinations starting at a few months old to develop lasting protection. The maternal antibodies buy time, but time is often exactly what a newborn foal needs—time to grow, time to develop, time to be ready for its own immune challenges. That's the gift of proper maternal vaccination.