From little acorns…..

In our monthly equine veterinary feature Dr Sarah Davidson BVMS MRCVS Assistant Vet at Sussex Equine Hospital outlines the problems of acorns, oak leaves and oak  bark which are poisonous for equines.

Sarah Davidson, Veterinary Associate, Sussex Equine Hospital

They are  everywhere at this time of year and a sure-fire sign that it is Autumn. Unfortunately, though, they are frequently left off the list of things that can cause harm to your horse.

Acorns, oak leaves and oak bark as well, are poisonous to horses although the toxic level is not actually known. This is because, as well as individual horse tolerance, the toxin levels vary greatly depending on season and from one year to the next. A horse that eats a few acorns will most likely be fine but those that prefer to crunch through acres of acorns instead of grass may be in trouble.

The cause of the symptoms is tannic acid in the oak being absorbed into a horse’s tissues throughout the body which drives out the normal intracellular fluid. This, in turn, results in kidney damage and intestinal damage which may or may not be reversible.

If a horse has plenty of other things to eat, it will usually shun acorns because they are in fact bitter to the taste. However, some horses will choose to eat acorns purely because they are on the ground and regardless of other options. This first sign that a problem may be brewing is a horse that is ‘just a bit quiet’. This then progresses over the following 24-48 hours to:

  • Loss of appetite
  • Blood in urine/more frequent urination
  • Increased thirst
  • Colic
  • Diarrhoea +/- blood
  • Mouth ulcers
  • Filling of the legs below the knee/hock

More serious clinical signs are rare and usually seen after longer periods of acorn ingestion or initial clinical signs going unnoticed. These include:

  • Weight loss/emaciation
  • Slow/irregular heart beat
  • A down horse
  • Poor hair coat
  • Ammonia smell from the mouth

If you suspect that your horse has any of these signs you should call your vet immediately. The vet will most likely take blood for assessment as well as perform a full clinical examination. Specific diagnosis of acorn poisoning can be tricky, but treatment is largely symptomatic with varying success depending on how much damage has been done.

First and foremost, fluids will be delivered to combat the dehydration, support the kidneys and in severe cases support the circulatory system and attempt to prevent shock. Other treatments include pain relief and intestinal support to help with diarrhoea and/or the passage of any acorns that may remain in the digestive system.

In summary, acorn poisoning is rarely seen in practice but can have severe consequences and even be fatal. As with all things, prevention is better than cure and sectioning off areas of the field that have overhanging oak trees before the autumn months is the best way to prevent your horse from becoming unwell.


Leave a Reply