With all the ghouls and ghosts ready to play their tricks this Halloween, it’s easy to forget there’s a much more sinister threat lurking high in the shadows. For your horse, it’s the small, poisonous bombs drifting slowly from the trees that we all need to pay attention to. Falling leaves can pose a potentially deadly threat to our horses. To help us all stay safe, here’s a list of trees that are highly toxic to horses.

Red Maple (Acer rubrum)

For these trees, poisoning usually occurs in late summer and autumn, when their leaves fall and drift onto pasture areas. Red maple leaves are HIGHLY TOXIC to horses. While ingestion of 1.5 lbs is toxic, digesting 3 lbs or more is fatal. Essentially what happens is that the chemicals in Red Maple leaves cause massive destruction of a horse’s red blood cells. Symptoms of poisoning include breathing difficulty, jaundice, urine that is dark brown in appearance, increased heart and respiratory rates, and lethargy. Between 50% and 75% of affected horses will die or have to be euthanized. The best thing to do is check areas where your horse frequently roams. Do not put leaves in their hay and make sure there are none within reach of their pasture area. If your horse does accidentally swallow Red Maple leaves or if they’re showing symptoms of poisoning, call your vet immediately.

Oak (Quercus species)

Oak trees in or near horse pastures don’t need to be cut down, but their branches should be kept out of the reach of any horses. The best thing to do is fence out areas where wilted oak leaves and acorns are plentiful, especially if forage is scarce. Oak leaves and acorns are poisonous to horses in large amounts due to their toxin tannic acid. This chemical can cause kidney damage and gastroenteritis. The Symptoms of Oak poisoning include lack of appetite, depression, constipation, diarrhea (which may contain blood), blood in urine, and colic.

Cherry and Plum Trees (Prunus species)

Cherry trees, plum trees and their relatives actually produce cyanide-containing compounds. That’s literally the same deadly poison used in any great Cold War spy movie. This toxin is found in the leaves, the fruit itself, and their pits. The plants are most toxic when drought or frost stresses them. Symptoms to be aware of include anxiety, weakness, heavy breathing, flared nostrils, and convulsion which all can eventually lead to death.

Just 1/4th of a pound of these leaves is so fatal, it can kill a 1,000 lb horse. Once the plant material is chewed and exposed to the acid within the horse’s stomach, hydrogen cyanide is released and rapidly absorbed into the horse’s bloodstream. Essentially, this chemical prevents living cells from being able to receive oxygen. As a result, an affected horse’s blood is bright cherry red because it’s overloaded with oxygen that cannot be used.

Black Walnut (Juglans nigra)

Your horse can be exposed to Black Walnuts from trees that grow around their pasture land or, more commonly, from shavings used in their stall bedding. Shavings with as little as 20% black walnut content are toxic to your horse. The effects of Black Walnut poisoning happen incredibly quickly, usually within 24 hours after your horse has been exposed. Fortunately, Black Walnut toxicity is usually nonlethal if you can get your horse the proper treatment. Signs to look for with Black Walnut toxicity include laminitis (which will worsen with continued exposure), reluctance to move, increased temperature and heart rate, difficulty breathing, digital pulse, limb edema, and increased gut sounds. If you suspect your horse has been poisoned by Black Walnuts, remove their stall shavings immediately. Cooling their legs and hooves with a hose can help make your horse more comfortable. If caught relatively quickly, your horse shouldn’t suffer any permanent effects. In cases of severe laminitis and edema, consult your veterinarian.

Raked Leaves

That’s right, any pile of leaves can cause injury if ingested by your horse. Horses love the taste and smell of recently fallen leaves. The problem is that leaves are dense and can compact in your horse’s digestive system and cause compaction colic. Make sure no one is disposing their raked leaves into your pasture.

Horses are much more likely to munch down on wilting leaves if they’re not getting enough of the proper nourishment. Be sure to feed your horses plenty of premium quality forage and make sure they’re drinking adequate amounts of water. To help ensure you’re giving your horse the proper amount of forage, we’ve introduced a new and improved Feed Calculator to Standlee’s new website. Try it out for yourself by clicking the button below.


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