Are acorns that fall from oak trees harmful to horses?
Most species of oak contain toxic phenolic compounds (tannins). Large quantities of young leaves and sprouts are toxic when consumed in the spring as are green acorns in the fall. Poisoning usually occurs when a large part of the diet is oak buds and young leaves, or green acorns, over a period of time. Ripe acorns that fall from the trees are usually less toxic. Acorns are very bitter, and most horses will avoid them if they have adequate forage and exercise. However, if you have a horse that has developed a taste for acorns, it would be a good idea to limit his access to the source. The first signs you will see when a horse is suffering from oak poisoning is that it will stop eating, become depressed, and develop colic.