Botulism is one of the most potent toxins known, and unfortunately horses are extremely susceptible to it. There are three types of botulism recognised in horses, all of which can be easily prevented.

Botulism is caused by toxins produced by the bacterium Clostridium botulinumC. botulinum is present in soil as spores, especially in certain areas of the United States and in Europe, although rare in the UK.
The spores germinate into bacteria that produce a neurotoxin that affects the brain and nervous system. The three types of botulism are contracted as follows:

  • Horses usually ingest these toxins in their feed, eg hay/grain/treats; this is sometimes referred to as forage poisoning.
  • Foals ingest bacteria that multiply in the gut which then produce toxins.
  • Although uncommon, botulism can also be contracted via wounds, either contaminated surgical wounds or traumatic wounds.
  • Botulism isn’t contagious, but outbreaks may occur if lots of horses eat contaminated food.

The toxins involved affect the nerves and muscles therefore common signs of infection include difficulty chewing/swallowing and progressive weakness, culminating in the inability to stand, and sometimes death.
Other signs include muscle shaking, difficulty walking, inability to lift the head, and loss of tail and eyelid tone.

A simple test is to offer the horse food; horses with botulism are usually unable to eat the food normally (they don’t use their lips) or swallow (you may see a mixture of saliva and food draining from the nostrils).
Your vet will check all your horse’s clinical signs and will perform a thorough physical examination. Blood and/or faecal tests may also be helpful.

Treatment is expensive and time consuming as most horses often require intensive care with constant nursing and feeding care to survive. Severely affected horses may also require a sling to assist them to stand.
Botulism anti-toxin can be administered, but once the toxin has affected the nerves, the damage cannot be reversed; at this stage the body then has to heal itself, which can take many weeks. Other treatments may include antibiotics, intravenous fluids and feeding the horse through a tube a few times per day.
Unfortunately, severely affected are likely to develop severe problems such as paralysis and the complete inability to breathe, which inevitably leads to death.

Vaccination and proper feeding practices are essential in at-risk horses.
The decision to vaccinate your horse against botulism depends on the horse’s individual risk factors, ie geographic location, travel/competition plans, potential for exposure to other horses, age, breeding status and overall health. Consult your vet about which vaccines are appropriate for your horse.
All hay and feed should be purchased from a reputable source to ensure it isn’t contaminated.