By Jess Hallas-Kilcoyne

Commonly found in soil, decaying animal carcasses, and, sometimes, decaying plant material, Clostridium botulinum is the bacterium responsible for producing the toxins that cause botulism. These powerful toxins prevent the release of neurotransmitters that control muscle contractions, resulting in weakness and, often, paralysis. Botulism in horses, as in humans, is frequently fatal.

Causes: The majority of botulism cases in horses occur as a result of the ingestion of feed or water that is contaminated, usually by the carcasses of small animals such as rodents or birds. Improperly preserved or spoiled haylage, or hay silage, is another common cause of equine botulism.

While far less common, botulism can also result from a wound or surgical site that becomes contaminated with Clostridium botulinum.

Finally, botulism can be caused by the toxins that are released when ingested spores of Clostridium botulinum are activated in the horse’s intestinal tract. It’s this type of botulism that is thought to cause Shaker Foal Syndrome, a usually fatal disease that affects young foals.

Clinical Signs: Botulism in horses is characterized by muscle weakness progressing to inability to stand and, eventually, paralysis. Other symptoms include muscle tremors, loss of control over the tongue, inability to swallow, and loss of tail tone. Unless humanely euthanized, death usually results from the paralysis of the respiratory muscles, causing the horse to suffocate.

Treatment: An anti-toxin for botulism is available, but it is very expensive. If administered after the toxin has already bound to the nerves in the muscles, the nerves must repair themselves by growing new nerve endings, a process that can take weeks.

Affected horses often need to be hospitalized so they can receive intravenous fluids and round-the-clock care, which usually involves feeding via stomach tube.

Prevention: A vaccine for the type B botulinum toxin – the strain most frequently linked to cases of botulism in horses in North America – exists, and is highly recommended if your horse lives in a high risk area or if you feed haylage. Previously unvaccinated horses receive an initial series of three monthly vaccinations followed by annual boosters.

This article originally appeared in the HORSEJournals.com E-Newsletter. To subscribe, please click on the sign-up box below.