Quantity
A few apple seeds are unlikely to harm a full-sized horse — the dose per seed is small. But a pile of apple cores or pomace from pressing is a different story. For cherry pits and peach pits, fewer are needed to reach a dangerous dose. Wild cherry leaves and bark are the highest concentration source and can be lethal from a single branch worth of browsing.
Notes
The most dangerous scenario isn't someone feeding an apple with seeds — it's a wild cherry tree dropping a branch into a paddock after a storm. Wilted cherry leaves concentrate cyanogenic glycosides and become more palatable (they lose their bitter taste). A horse browsing on a single downed cherry branch can ingest a lethal dose. Apple seeds in small numbers (a few cores) are low risk for a full-sized horse, but large quantities — like a bucket of pomace from cider making — are dangerous.
Negative Signs
* Rapid, heavy breathing (the body tries to get more oxygen, but cells can't use it)
* Bright cherry-red gums (the blood is oxygenated but the cells can't extract it)
* Rapid heart rate
* Excessive salivation and drooling
* Muscle tremors
* Staggering and collapse
* Seizures
* Sudden death in severe cases — particularly from wild cherry
FAQ
Q: I always feed my horse whole apples. Do I really need to remove the seeds?
A: A few apple seeds from one or two whole apples won't harm a full-sized horse — the dose of cyanogenic glycoside per seed is very small. But it's good practice to core apples before feeding, especially for ponies and smaller horses. The bigger concern is large quantities: a bucket of apple cores, cider pomace, or access to windfall apples under a tree.
Q: There's a wild cherry tree at the edge of my horse's field. Is that dangerous?
A: Yes — particularly after storms or frost. Wilted cherry leaves are among the most concentrated sources of cyanogenic glycosides, and horses find them more palatable than fresh leaves. Fence off the tree with a wide margin, or better yet, have it removed. Check the fence line after every storm for fallen branches.
Alternatives
Feed apples sliced with seeds and core removed. If you have fruit trees in or near your paddock, fence them off and clean up windfalls promptly. Identify and remove wild cherry trees from paddock boundaries — or at minimum, fence them off and check for downed branches after every storm.
Risks & Disclaimer
If your horse ate a large quantity of fruit pits or seeds, or has been browsing on wild cherry trees (especially wilted branches after a storm), call your vet immediately. Cyanide poisoning can kill within minutes to hours. If you can smell a faint bitter almond odor on your horse's breath, that's cyanide — this is a critical emergency.
