12/19/2002 Entry: "Plan Your Vaccination Schedule Now"

February 1998

Published by HorsePlay

Raymond Hyde, DVM

I had the displeasure one summer day of being called out by a new client to examine a two-year-old Appaloosa he had recently purchased in Florida. I found her lying in a semi-comatose state caused by Eastern equine encephalomyelitis.

The horse's owner told me he had gone to the local feed store to buy vaccines just after he had purchased her about a month earlier. However, he returned from the store empty-handed after the store clerk told him that it was too late for spring vaccines. I had to euthanatize the filly. Unfortunately, the store clerk and the filly's owner represent a large group of people who don't fully understand the diseases that threaten their horses or the best strategies for preventing them. With so many options available, your vaccination schedule could become confusing.

Not all diseases are a threat to all horses. Each horse's case is different. Geographic and logistical factors-how the horse lives and works-need to be taken into account when planning a vaccination schedule.

Preventable infections can be categorized by their source: I like to divide them into two groups: environmental and contagious. Environmental diseases are threats from the horse's surroundings and wild animals. Examples are rabies: a virus from the bites of raccoons, skunks, foxes, bats; tetanus: a clostridial bacteria found in soil and manure; it enters through wounds; eastern equine (EEE) and western equine (WEE) encephalomyelitis: viruses that are transmitted from birds to horses by mosquitoes; Potomac horse fever (PHF): an Ehrlichia bacteria of unknown environmental origin; botulism: another clostridial bacteria found in rotting vegetation and animal remains; leptospirosis: a bacterial disease caused when a horse consumes feed or water contaminated by the urine of infected wild animals or pigs. More common in cows and dogs.

These and other diseases threaten all horses depending on the incidence in their particular geographical location. To be safe, vaccination against the diseases listed above should be considered for all horses.

Contagious diseases are spread from one horse to another. They include rhinopneumonitis (rhino): a highly contagious virus causing respiratory illness, abortion, and paralysis. influenza: another respiratory virus infection; strangles: respiratory bacteria that causes abscesses. Individual or herds of horses that are kept completely isolated may not have to be vaccinated against contagious diseases, because there is no threat of exposure. This would not hold true for horses leaving isolation or if new horses are to be introduced to an otherwise isolated herd.

Vaccines for contagious diseases should be given at least 30 days prior to potential exposure (horse shows, fairs, trail rides, race meets.) They traditionally are given during the spring and fall for a few reasons. Spring vaccination against equine encephalomyelitis and Potomac horse fever maximizes immunity during mosquito/insect season to reduce the incidence of these insect-borne diseases. The immunity induced by some vaccines does not last 12 months, so they may need to be repeated at two- to six-month intervals (rhino/flu) or six- to 12-month intervals (EEE/PHF). For convenience, the horse's other vaccines are often given at the same time (see chart below).

Commonly Used Vaccination Schedules

Horses with exposure to other horses: Twice yearly vaccinations
Spring: EEE, WEE, tetanus, PHF, rhino, flu, botulism
Fall: rabies, PHF, strangles, rhino, flu, endobactoid (a vaccine that protects horses against endotoxemia, a poisoning of the horse by specific bacteria, which can lead to life-threatening shock)

Horses without exposure to outside horses
Spring: EEE, WEE, tetanus, PHF, rabies, botulism

Broodmares
every 60 days throughout pregnancy: rhino
30 to 60 days prior to foaling: EEE, WEE, tetanus, PHF, rabies, botulism, rhino, flu

Foals
give initial vaccines at three to four months of age, followed by boosters (except rabies) in three weeks.

The newer multiple-disease vaccines (a "five-way," for example, which includes EEE/WEE/tetanus/flu, and PHF or rhino) greatly reduce the number of injections that have to be given and cause little reaction in most horses. Bring a new horse's vaccinations up to date as soon as you get him, depending on his prior vaccination history and on any new risk of exposure. Horses who head south for the winter should be given a EEE/WEE booster in the fall. If you don't know your horse's history, vaccinate anyway to be safe.

Keep good vaccination records to avoid a costly mistake; group records are better than no records, but an individual history is best. Consult with your veterinarian to determine your horse's vaccination schedule; individual needs vary.