Botulism in Horses

Over the past couple of weeks, two calls have come into the Extension Office concerning botulism in horses.  Because these calls came so close together, this subject should probably be addressed.

Botulism is a deadly disease caused by the toxins produced by the bacterium Clostridium botulinum.  This is a potent neurotoxin that impairs nerve function, which can cause paralysis of muscles.  Therefore, this disease is often deadly.

C. botulinum is an anaerobic (lives without oxygen), gram-positive, spore forming bacterium.  The clostridium family can cause several different diseases such as botulism, tetanus, blackleg and malignant edema.  These can be rapid, severe and deadly diseases that sometimes show no clinical signs; the animal is simply found dead.

The bacterium and its spores are widely distributed in nature. They are found in soil, sediments of streams and lakes.  They can also be found in the intestinal tracts of fish and mammals. The bacteria will produce toxins under conditions of decaying plants and animals.

Adult horses can be get botulism in two ways: 1) By consuming feed or forage containing the pre-formed toxins of C. botulinum (known as forage poisoning). 2) Through wounds contaminated with the bacteria, generally puncture wounds.

Botulism from forage poisoning can occur when animals eat forage that has spoiled or any type of feed that has been contaminated by a decaying animal.  Spoilage can occur when hay is baled at too high of a moisture content.  Additionally, hay that has been fed or has spilled onto the ground and has mixed with soil and feces provides a greater risk for horses contracting botulism.  If dead animals accidentally get baled into the hay, botulism can occur.

The clinical signs of botulism in horses include weakness; decreased muscle tone of the tail, eyelid, and tongue; trembling; dilated pupils; lying down; difficulty in swallowing; drooling; and green or milky nasal discharge.  Horses progressively get weaker, and once the diaphragm muscles become involved, respiratory failure occurs, and the horse dies of asphyxia.  The disease can hit suddenly and result in the death of horses that were perfectly healthy the day before. Botulism causes a flaccid paralysis, unlike tetanus that causes a rigid paralysis.

Treatment for botulism is an administration of an antitoxin.  This should be done early in the clinical signs to have any chance of success.  However, treatment is costly, difficult and often too late.  Therefore, it is better to prevent the disease.

Prevention includes being diligent about feeding a good, quality hay and other feedstuffs.  Any questionable feed should be eliminated.  Additionally, there is a botulism vaccine.  Talk with your veterinarian about an appropriate vaccination schedule for your horses. 

An additional article can be found here:

http://www.cahfs.ucdavis.edu/local-assets/pdfs/Equine%20botulism%20fact%20sheet.pdf

An audio entitle "Preventing Botulism in Horses" can be found at this link:

http://news.ca.uky.edu/audio/preventing-botulism-horses

 

The above article was originally written by Fernanda C. Camargo, Bob Coleman, Laurie Lawrence, Department of Animal Sciences at the University of Kentucky; adapted by Kim Woods, Person County Cooperative Extension