Plants Poisonous to Horses - Oak and Acorn - Quercus species

All parts of the Oak tree are toxic to horses, (the toxic principle being gallotannin). 

Oak poisoning causes gastroenteritis and kidney damage in horses.

Poisoning usually occurs when horses graze on oak due to lack of adequate forage but some horses do develop a taste for acorns and will seek them out.

Symptoms may appear several days after ingestion and include: 

Abdominal pain, 
constipation followed by diarrhoea (sometimes bloody), depression, 
frequent urination,
discoloured urine, 
jaundice, 
colic, 
sweating,
unsteadiness,
fits 
and 
coma.

Oak poisoning is often fatal, extreme care should be taken to remove all acorns from pasture. Also be aware that if there are oaks in the vicinity storms can blow the leaves into your pasture.

Image:    © Copyright Brian Robert Marshall and licensed for reuse under this Creative Commons Licence.