Horse owners understand that vaccinations protect the health of their horses and might even be life-saving. What some owners might not realize is that adverse reactions can occur after vaccination. While most vaccines' side effects are minor, it's important to know when not to worry and when to call the veterinarian.

"It's important to remember that annual vaccinations are the best way to help prevent potentially deadly equine diseases and help keep horses healthy," says April Knudson, DVM, equine specialist for Merial's Large Animal Veterinary Services.

"Equally important is the understanding that some horses may experience an adverse reaction following vaccination. That reaction, however, will likely be far less devastating than if the horse actually acquired the disease for which it was being vaccinated against."

Vaccines are designed to stimulate an immune response, notes Knudson. Each horse is unique and one horse's specific immune response might differ from another's