There are different ways for a horse to become infected: through an open wound, much like tetanus, and through
ingestion, when eating feed or hay containing decaying matter.
Dead rodents or other animals have been known to be incorporated into hay bales. The decaying matter releases the botulism toxin and the horse ingests it when he eats or drinks.
The first sign of botulism may be difficulty in closing the eyelids or in swallowing. Horses stand with their muzzles in the food or water bucket because they are hungry but cannot swallow.
The animal may tremble, lie down more than usual and may exhibit poor or weak tail and tongue tone. As the disease progresses, paralysis of the respiratory muscles leads to suffocation and death.
Foals that are affected typically, show an inability to nurse. The foals' muscle tremors have lead to botulism in youngsters being called "shaker foal syndrome."
There are different types of botulism toxin, with Type B being most common. It is found in the soil of central Kentucky and along the eastern seaboard. Type C, common throughout Europe and believed to be the type that killed the yearlings in Australia, is rare in the United States except in areas of Florida.
Previously, more than 90 percent of infected horses died from this disease. The development of an antitoxin and good care in assisting nursing, drinking, and eating have increased a horse's chance of survival to nearly 70 percent.
Unfortunately, botulism antitoxin is not widely available, and it is expensive. It works best when used early in the course of the disease, but too often the early signs of botulism go unnoticed. The antitoxin is helpful, but prevention with vaccination is the best approach.
An excellent vaccine is now available for at-risk horses in areas with high botulism potential. The recommended routine calls for three vaccinations one month apart, then yearly boosters.
Pregnant mares should be re-vaccinated about 30 days before foaling in order to pass on protection to the foal.
WEATHER IS A FACTOR in botulism incidence. A cold, wet winter is thought to produce conditions favorable to the growth of the botulism organism, which may explain this year's increases. If horse owners in the susceptible areas vaccinate their animals, botulism may go back to the list of seldom-seen diseases.
Feeding your horse high-quality feeds from reputable sources is also a good way to reduce the risk of botulism.
If you have questions about botulism or if your area is at-risk, consult your veterinarian.