Botulism Suspected in Wyoming Horse Deaths
Botulism is suspected in the deaths of 10 horses on a farm in Wyoming, USA. Very few details are available to indicate why botulism is suspected or what the source might be. It was reported that six horses died initially, and four others that were lethargic and unable to stand died within 24 hours. These signs fit with botulism, which is characterized by profound muscle weakness and progressive paralysis. Death is caused by an inability to breathe when the paralysis starts to affect the muscles that control breathing. Making a diagnosis of botulism can be difficult in horses - it is often a "diagnosis of exclusion" whereby the diagnosis is made because everything else that could cause the condition has been ruled out. Testing of some of the affected horses is underway. It was not reported whether possible sources of the disease (e.g. feed) are also being tested.
Botulism is caused by a toxin produced by the anaerobic bacterium Clostridium botulinum. In adult horses, the disease almost always occurs from consuming the toxin in contaminated feed. If the bacterium (which can be found in the soil in many regions) gets incorporated into feed, under the right conditions the organism will grow and multiply, and produce the powerful neurotoxins that cause botulism. Fermented feeds like haylage and silage are common sources, because the way they are stored is more likely to create an environment where C. botulinum can grow. However, various other food sources have also been implicated in some outbreaks.
Botulism is rare, but typically fatal in adult horses. Some basic tips to reduce the risk of botulism are:
- Avoid feeding horses haylage and silage, especially in areas where botulism is more common. There are some benefits to using feeds, so they are commonly used in some regions, but if you use fermented feeds you should discuss the risk of botulism with your local veterinarian, and take measures to reduce the risk of C. botulinum growth.
- Vaccines against botulism are available. Adult horses are usually not vaccinated, other than mares which are vaccinated to reduce the risk of botulism in their foals (known as "shaker foal syndrome"). Adult horses being fed high-risk feeds could be considered for vaccination, but if the feed is so high risk that vaccination is warranted, perhaps the feed program should be reconsidered. Furthermore, there are several types of C. botulinum, but the vaccines only protect against some of them. If you are thinking about vaccinating, you should make sure that the vaccine you're going to use protects against the botulism strains found in your area.
If you ever have a horse that is showing signs of botulism (e.g. weakness, difficulty rising, dropping food out of its mouth, difficulty swallowing), or if botulism is suspected in a sudden death, immediately stop feeding any potential high risk feeds until the cause of the disease is identified. This might help reduce the number of affected horses.
More information on botulism can be found in our botulism archives. An information sheet about botulism in foals can be found on the equIDblog Resources page.
I went to work as head wrangler at an upmarket kids camp. 70+ staff, 140+ kids and 66 horses. The management know nothing about horses apart from renting them. We had 66 horses delivered by a horse rental company. They were neither wormed nor had shots. The facilities had no shelter or provision for a sick or injured animal. The feed budgetted was insufficient for even a maintenence diet.
My requests that we should meet a basic standard of care in feeding and worming them went unheard. Despite explaining clearly what I was talking about and showing them some basic information I could not get the message across. As I was responsible for their care I had to resign after 2 weeks as a result.