Botulism is also called clostridal disease, limberneck or forage poisoning. No matter what you call it, it is potentially lethal for a horse and mostly preventable. The main cause of botulism is a horse eating spoiled feed, hay or drinking water that was contaminated with spoiled feed or hay. “The Complete Equine Veterinary Manual” (David & Charles, 2004) claims that botulism is on the increase in horses due to big bale silage.
The actual toxin that causes botulism is a bacterium called Clostridium botulinum. Once it takes a hold of a horse, prognosis is grim. Only mild cases caught early enough have any hope of surviving. This is because botulism paralyses the horse’s ability to breathe and swallow. Sometimes botulism acts so fast that the horse just drops down dead before manifesting any symptoms.
What Is Big Bale Silage?
In big bale silage, hay is stored in massive bales, usually inside of plastic casings inside of a warehouse. These round bales are far bigger and far heavier than the traditional hay bale. This method of storing hay can often extend the life of the hay but it can also harbor numerous bacteria at the center of the bales. It is fed to many animals, including horses.
How did Clostridium botulinum get inside of these bales? Usually from the carcasses of dead animals, often rodents, that were unlucky enough to be cavorting in the hay at the time it was being baled. As they rotted, the deadly bacterium was released into the surrounding hay.
The bacterium is even more pronounced in hay cubes or hay pellets often fed to horses. Unlike regular hay, there’s no way for a horse to pick and choose what strands to eat. Although a tremendous amount of heat is used in the hay cube making process, it’s not enough to kill botulism spores.
Other Types
Another source of botulism in horses is when they eat lawn clippings. Soon after being mowed, blades of grass begin the decomposition process. Even though lawn clipping may look good and smell good to humans and horses, it is a lethal treat.
Yet another form of botulism is commonly called shaker foal syndrome. These foals have either been born to mares that weren’t vaccinated against botulism or have been exposed to botulism through contaminated food. The immune systems of foals under six months old are very weak in comparison to the immune system of an adult horse, so just the slightest exposure can get a foal gravely ill.
Prevention
There is a vaccine available for horses, one of which is called BotVaxB. All horses should be vaccinated, because you never know when they are going to get exposed to contaminated feed.
Hay should ideally be purchased in small bales and each flake should be checked before giving to the horse.
References:
“The Complete Equine Veterinary Manual.” Tony Pavord, MRCVS & Marcy Pavord. David & Charles; 2004.
Ontario Ministry of Agriculture, Food & Rural Affairs. “Botulism in Horses and Haylge.” http://www.omafra.gov.on.ca/english/livestock/horses/facts/info_botulism.htm
Iowa State University. “Botulism.” http://www.cfsph.iastate.edu/Factsheets/pdfs/botulism.pdf
