Fall Leaves - Are They Toxic to Horses?

veterinarian.

Oak (Quercus species) Oak trees in horse pastures should not be cut down, but branches should be kept out of reach of horses. Horses should be fenced out of areas where wilted oak leaves and/or acorns are plentiful. In large amounts, the leaves and acorns are poisonous to horses due to the toxin tannic acid and they cause kidney damage and gastroenteritis. Horse owners are encouraged to fence off oak trees from their pasture, especially if forage is scarce. Symptoms of poisoning include lack of appetite, depression, constipation, diarrhea (which may contain blood), blood in urine, and colic.

Cherry and Plum Trees (Prunus species) Cherry and plum trees and their relatives (peaches, nectarines, apricots and almonds) have cyanide-containing compounds, which are found in leaves, fruit, and pits of the trees. The plants are most toxic when drought or frost stresses them. Wilted leaves are also quite toxic. Symptoms include anxiety, weakness, heavy breathing, flared nostrils, convulsion, and death. The problem is caused by cyanide re-released; the plants contain trace amounts of hydrogen cyanide, but on decomposition after crushing and exposure to air or on digestion, poisonous amounts may be generated. Only one-quarter pound of leaves per 1000 pound horse can be fatal. Once the plant material is exposed to the acid within the horse’s stomach, hydrogen cyanide is released and rapidly absorbed into the horse’s bloodstream. Cyanide works as a poison in that it prevents normal cellular uptake of oxygen. As a result, an affected horse’s blood is bright cherry red because it is overloaded with oxygen that cannot be utilized.

Do not dispose of your raked leaves into your pasture. Horses like the taste and smell of recently fallen leaves. Leaves are dense and can compact in the horse’s digestive system and cause compaction colic. Leaves may also come from plant species that are poisonous to the horse. Be aware of leaves and trees that are toxic to your horse and fence off wooded areas or fence rows that contain possible toxic substances. If branches fall into the pasture make sure they are removed immediately.