Horse Vaccination and Deworming Primer
Learn how vaccines and dewormers work, how to make the most of them and what type of rotation schedule to use to keep your horse healthy.

An effective vaccination and deworming program is a critical component to keeping your horse healthy.

Vaccinations help protect your horse against diseases by stimulating his immune system to fight back when he's exposed to a virus or bacteria. When your horse is vaccinated, he's administered a dose of antigen, which usually consists of an inactivated portion of a disease-producing organism. The specific antigen is injected into his muscle and activates his immune system to produce antibodies against that organism. These antibodies are the body's disease-fighter defenders.

Do Vaccines Really Work?
Most vaccinations are effective to a certain degree and will usually either prevent your horse from getting sick or will reduce the severity and duration of his signs if he does get sick.

The following facts about vaccine testing will explain what we know about vaccine efficacy and what the pitfalls are.

Approval requirements: To be approved and licensed by the U.S. Department of Agriculture (USDA), a vaccination must demonstrate a certain increase in the number of antibodies-called a rise in antibody titer-following administration. But, we don't always know that an increase in the number of antibodies will effectively fight disease.

Challenge studies: In some cases, challenge studies also are performed during the prelicensing stage of vaccine development. During this study, both vaccinated and unvaccinated horses are exposed to a specific disease, and the difference in the number of horses that get sick and the severity of their signs are recorded. Challenge studies are generally believed to be a more effective indicator of a vaccine's effectiveness than a simple rise in antibody titer. Unfortunately, challenge studies are difficult and expensive to carry out, and therefore often not performed.

All of this means that, even with USDA approval, we don't always know whether a given vaccination will actually provide complete protection against the disease in question-or if it does, just how complete that protection will be.

Making the Most of Vaccinations
Take the following steps to ensure the vaccinations you administer will be as effective as possible.

1. Maintain all of your horses on the same vaccination schedule.
2. If you are administering vaccines yourself, make sure you can do it properly.
3. Obtain your vaccines from a reliable source--where they've been kept in a clean, refrigerated environment. If they become contaminated, you could risk an injection-site reaction.

1. Acute allergic reactions-called anaphylaxis. In this situation, your horse's immune system responds too strongly to the antigen that's administered-leading to events that can result in collapse or even death. Anaphylactic reactions, although frightening, are extremely rare.
2. Local injection site reactions-ranging from sore spots in the muscle to the formation of an abscess. Note: Abscesses can occur if bacteria enter the skin during the vaccination processes, although it's also possible for your horse to develop a sterile abscess-one that contains no bacteria-simply because of the way his body responds to the vaccine.

Daily deworming: You'll administer a daily dose of the deworming agent pyrantel tartrate in your horse's feed. You'll still need to administer some oral deworming products to cover all parasites.

Interval deworming: You'll give your horse a dose of paste dewormer every eight weeks.

What to Give When
The following is a chart of what to give when for both vaccines and dewormers.

*Often vaccines such as EEE/WEE (Eastern and western encephalomyelitis), tetanus and flu are combined.
** Give pyrantel tartrate daily.

Barb Crabbe, DVM, is an equine practitioner in Oregon City, Ore., whose practice is 70 percent dressage horses. A lifelong horsewoman, she is an equestrian journalist, a U.S. Dressage Federation "L" graduate and has competed through Prix St. Georges.

For more information on vaccinations, read Barb Crabbe's complete article "Vaccination & Deworming: The Old, The New & What's Ahead," in the April 2002 issue of Dressage Today magazine.