My mare reacts badly to vaccines and has not received any for maybe 5 years because of it. What is the best way to deal with immunization for her upcoming foal?
Foals are born with no natural immunity to disease, so they obtain protection by ingesting colostrum immediately after birth from their dam. The maternal antibodies in colostrum are absorbed through the gut via a process called “passive transfer”. Failure of this will result in a foal that is very prone to overwhelming infections (sepsis) and other health complications. The quality and level of antibodies in colostrum is directly dependent on the mare’s immune status, so the colostrum from unvaccinated mares won’t provide coverage for tetanus, rabies, and most of the disease that we try to protect horses from with vaccination. Since you can’t vaccinate a very young foal, there is a several month period where they are quite vulnerable to these infections. The old habit of giving tetanus antitoxin to a newborn has fallen out of favor because the antitoxin (which provides immediate protection, not like a vaccine) can cause devastating serum sickness and liver damage. To ensure maximum colostrum quality, we give mares their booster shots about a month before foaling so their antibody levels are peaking near birth. If your mare reacts badly to vaccines, I would find out which ones are problematic and decide on a schedule that allows you to either prepare her for that shot with some banamine, or decide if you can safely skip it. Many horses are given the more economical “5-way” vaccine which combines multiple vaccinations in one shot. While this is more convenient, I have found the adverse reaction rate to be much higher than when vaccines are split into individual doses and administered over a couple of visits. That way you can also identify if your horse is sensitive to a particular vaccine, and gives you the opportunity to plan for the next shot or try a different brand of vaccine. I suggest that you discuss this with your vet well in advance of her due date so you can come up with an appropriate strategy to protect the health of her baby.
Melissa McKee DVM