Friday, 26 February 2016

All About... Botulism.

What is Botulism?

It is a deadly disease which is caused by toxins produced by Clostridium botulinum – a bacteria.  This toxin is very potent and impairs nerve function causing paralysis.  This includes the nerves of the diaphragm which will mean the horse will stop breathing and therefore will die. Clostridium botulinum is a spore forming bacterium and is found in soil, river and lake sediment and in the intestines of fish and mammals.  The incidence of botulism in horses is low, especially in the UK, however, the mortality rate is high. Once the toxin enters the body it will reach the  bloodstream and be distributed to nerves all over the body it will then prevent muscles contracting – leading to paralysis.  This happens rapidly, taking 1 to 2 days to cause death.

  • Weakness 
  • Trembling 
  • Dilated pupils 
  • Standing with all 4 feet close together 
  • Lying down 
  • Difficulty in swallowing 
  • Drooling 
  • Nasal discharge either green or milky 
  • Decreased muscle tone 
  • Botulism hits suddenly.


There are 3 ways for a horse to get botulism:
  • Consuming forage or feed which contains the bacteria.  When the food reaches the intestines the bacteria will produce the toxin. 
  • Consuming the feed or forage which already contains the toxins. 
  • Through a wound which becomes contaminated with the bacteria eg: puncture wounds.  The wound will close thus providing an ideal environment for the bacteria to produce toxins.

If hay has been baled with a high moisture content it is more likely to become spoiled and therefore contaminated.  Silage should not be fed to horses because of  the moisture content providing ideal conditions for the spores to form (cattle do not develop the disease as easily).  Also, eating hay that has spilled on the floor and mixed with soil and faeces will increase the risk.  If a dead animal or bird is accidentally baled in the hay then the body will provide an excellent place for the botulism toxins to be produced.  

The vet will use the clinical signs, history and observation to diagnose.  It is often the case that several horses will be affected if they have access to the same contaminated feed or forage.  Blood tests are often normal.

Adult horses are sometimes able to cope due to the ‘good bacteria’ in the intestines.  However, it is often too late for treatment and prevention is better.  There is an antitoxin available which will help in the early stages.  Euthanasia is often the kindest choice.

Do not feed silage to horses.  Hay with damp or rotten areas should not be fed and haylage must be fed within the recommended date.  

Botulism is a horrible disease so it is vital that food is sourced from reputable companies and stored carefully.  Forage should be produced and stored to reduce the chance of providing conditions which the bacteria thrive in!

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