By Maegen Brown CVT, Apr 12 2017 01:09PM
Due to a recent outbreak of feed acquired Botulism toxicity in a large population of horses in Eastern PA, we wanted to revisit what Botulism toxicity can do in horses. Botulism is a highly fatal neurologic disease caused by the Clostridium botulinum bacteria. Despite horses’ large size, they are the most susceptible species to botulism toxicity. There are seven known strains of C. botulinum, types A through G. Types A and B are most common in horses and are usually acquired through spoiled forage sources or silage. This is a concern on dairy farms where the cows can be close to the horses making it possible for silage to contaminate the horses’ feed sources. Type C can be caused by a decaying dead animal in the feed or water. Type B is the only strain that has a vaccination marketed for use in horses. Types D through G have never been reported in horses in the United States. The bacteria produces a toxin, and it is the toxin that causes muscle weakness. The severity of the disease depends on the amount of toxin that is in the horse’s system, blocking transmission between the nerves and the muscles. If there is a minimal amount of toxin, recovery is expected, but a large amount of toxin can be fatal. Botulism treatment includes a combination of antitoxin administration and supportive care.
After exposure, the botulinum toxin enters the bloodstream, circulates throughout the body, and enters various motor nerve cells. As a result, the horse becomes weak and potentially paralyzed. The earliest clinical signs of botulism in adult horses usually include drooling, dropping food, weak tongue tone, inability to swallow, and anorexia. The horse will most likely still have an appetite in earlier stages, but they will appear to be playing in their feed or water being unable to swallow. As the disease progresses, the muscle weakness worsens, breathing becomes difficult, and death can occur due to the paralysis of the respiratory muscles. Botulism is usually fatal if left untreated; however if treated, a horse can fully recover. So at the first signs it is important to contact your veterinarian, the more time that goes by without treatment; the lesser the chances of recovery.
Prevention is the best method to protect horses from acquiring Botulism toxicity. An intramuscular vaccine is the best preventative measure; it is given in three doses initially, then an annual single dose booster is required. Pregnant broodmares should be vaccinated for Botulism as part of their pre foaling vaccines. “Shaker Foal Syndrome” is generally seen in foals at 1 to 2 months of age, but it can develop as early as 2 weeks or as late as 6 months. Also, good husbandry around the barn can help. Be sure to never feed rotten or moldy grain or hay. Do not use this material as bedding either, as horses may still eat it. Keep water troughs and buckets clean. Be sure to properly dispose of any dead animal carcasses found on the property or in the field and pasture.