While I've had my horses snatch a mouthful of oak leaves while riding with no apparent harm, a large quantity can be dangerous.
Various varieties of oaks live throughout North America. Horses will eat the leaves if there is no other food available. Water may be contaminated by fallen leaves. Acorns are also toxic if eaten in quantity.
Signs of oak poisoning are:
- colic symptoms
- darkened urine
If you suspect poisoning from any plant or substance call your veterinarian immediately.