Question:
Are acorns toxic to horses? We have an oak tree that drops nuts each autumn and my horses seem to enjoy them as a treat. I’ve been told, however, that they are dangerous. Is it true that eating acorns can cause colic or laminitis? Organ failure? What are signs of acorn toxicity in horses? Are acorns from all varieties of oak trees toxic and how many would an average-sized horse have to eat before developing a problem? Can I just rake most of them up or should I remove my horses from the field where they accumulate each fall?
Answer:
Oak leaves and acorns are commonly eaten by livestock and wildlife with little or no trouble most of the time. However, when animals ingest a lot of acorns, usually over a few days in the autumn or spring, problems can develop. Oak poisoning is most often seen when other food isn’t available or when snow makes other forage sources inaccessible. All oaks appear to be toxic.
Potential dangers
Acorns, oak leaves, or oak leaf buds can cause direct damage to the intestinal tract and kidneys. How this happens hasn’t been completely worked out, but tannins in the acorns and leaves are believed to be involved. Goats, sheep, mule deer and pigs seem to be able to eat plenty of acorns because they have proteins in their saliva that bind the toxins and prevent damage.
Incidence
Oak poisoning is rare in horses, but it does occur. In cases recently reported in the United Kingdom, horses went off feed and had painful colic and/or diarrhea, which was often hemorrhagic (bloody). The onset of clinical signs was rapid and, unfortunately, two-thirds of the horses died within hours or days of becoming ill, due to severe damage to the intestines and kidneys. The authors who documented the cases noted that oak poisoning is more common in feral ponies in southern England.
What you can do to protect your horse
So the main conclusion is that yes, under some circumstances, horses can develop oak poisoning. Horses that nibble on a few acorns or oak leaves are probably going to be fine, but those that don’t have other things to eat can ingest dangerous amounts of oak leaves and acorns. It is probably best to keep horses out of pastures where oak trees are dropping large numbers of acorns to prevent overconsumption, and, in general make sure horses have plenty of other forage to consume besides acorns and oak leaves.
Karyn L. Bischoff, DVM, MS, MPH
Cornell University
College of Veterinary Medicine
Ithaca, New York
For autumn horsekeeping tips, click here.
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