I’ve heard about the dangers of horses eating red maple leaves, but recently heard that acorns can pose a threat as well. Is this true?
Oak (Quercus species) toxicity in horses is not common. While most portions of the oak tree—blossoms, buds, leaves, stems, and acorns—can be toxic, horses are often not affected because it requires eating a large number of oak leaves or acorns to show clinical signs.
When acorn toxicity does occur, the gallotannins present within oak leaves and acorns are broken down into several toxic products within the horses’ body. These toxins can then damage the stomach and intestinal lining, kidneys, and blood vessels. This can lead to symptoms such as colic, straining to defecate, diarrhea, and bloody-appearing urine. Treatment is aimed at correcting dehydration and electrolyte abnormalities, controlling gastrointestinal pain, and supporting kidney and intestinal function.
Keeping palatable forage sources such as grass or hay available when horses are turned out around oak trees will keep most horses from eating oak leaves, blossoms, or acorns. If you have a horse that finds acorns or other parts of oak trees particularly tasty, you may have to move their turn-out area or fence off the oak tree to limit access. A horse ingesting the occasional acorn or leaf during grazing does not pose a risk of toxicity.
Alisha Gruntman is an internist at the Hospital for Large Animals at Cummings Veterinary Medical Center. After completing her DVM at Purdue University, Dr. Gruntman completed her internship and residency at Cummings School of Veterinary Medicine. She commonly treats colic, colitis, enteritis, gastric ulcers, pneumonia, equine asthma, neurologic diseases, fevers of unknown origin, and more.