Acorns, oak leaves and their branches pose a toxicity risk to horses, large amounts ingested can induce severe illness. This is due to the tannic and gallic acids in the acorn, which can cause severe damage to the gastrointestinal system and kidneys.
There is anecdotal evidence that some horses develop a liking bordering on addiction for acorns and will actually seek them out, overindulging to the point of illness. Symptoms include Constipation, Anorexia, Colic, Blood in the urine, Kidney damage, Dehydration, Fluid accumulation in the legs (oedema)
Atypical Myopathy (AM)
In recent years this frequently fatal muscle disease has become more prevelant. Predominantly occurring during the autumn, AM results in damage to the muscle tissue and causes significant muscular pain.
Research has shown horses kept on overgrazed pasture with a large quantity of dead leaves and dead wood are at particular risk. The seeds of sycamore trees have been linked to outbreaks. The onset of AM is rapid, affected horses are often found at pasture, weak, unwilling to move and have difficulty standing. Other signs include; Muscular stiffness/tremors, sweating, depression, high heart rate, dark urine, breathing difficulty.