Can they eat it? / Onions and garlic
Can horses eat onions and garlic?
Careful. Large or regular amounts damage red blood cells.
A clove of garlic in a supplement is widely fed and generally tolerated; wild onion in pasture or bulk feeding causes anemia. Do not feed garlic daily at high doses.
Weakness, pale or yellow gums, dark urine.
Stop the feed and call your vet.
Why
Onions and garlic contain sulfur compounds, mainly N-propyl disulfide in onion and related thiosulfates in both. In the horse these are absorbed and oxidize hemoglobin inside red blood cells, causing them to rupture (Heinz body hemolytic anemia). The damage builds with repeated or bulk intake, so a single clove in a supplement is generally tolerated, while onion in pasture or heavy daily feeding is the real risk.
How much is too much
For a 1,000 lb horse, a clove or two of garlic in a supplement is widely fed and generally tolerated, but not daily at high doses. A few onion pieces is a small taste; a handful or more repeated over days is a real concern. Ponies, miniatures and horses with other health issues may react to less, so keep amounts smaller and ask your vet before offering regularly.
Horses
For full-size horses in work or at pasture, the main concern is wild onion or wild garlic growing in grazing areas and hay fields, which can be eaten in quantity. Check pastures in spring and after mowing, and keep fresh onions and garlic from kitchen scraps out of stalls and feed rooms. Routine supplements with a clove are usually fine, but avoid making them a daily habit.
Ponies and easy keepers
For ponies, miniatures, seniors and insulin-resistant or laminitis-prone horses, avoid feeding garlic or onion at all unless your vet approves, since these animals are often more sensitive to changes in red blood cell health and feed composition. Keep these horses away from onion-heavy scraps and clear any wild onion from their paddock. Watch for weakness, pale gums or dark urine after exposure.
Safe alternatives
For flavor and a treat, offer a small piece of carrot, a few apple slices (cored, no seeds), or a handful of fresh herbs like mint or parsley. Serve them in a bucket or hand-feed in small portions. These give your horse something to enjoy without the sulfur compounds that build up in red blood cells.
Questions people ask
Can horses eat garlic in hay?
Garlic in hay is unlikely to be harmful in small amounts, but avoid hay with wild onion or garlic growing in it. Check bales and remove any suspect material before feeding.
What if my horse ate a lot of onion?
Stop the feed, remove access, and call your vet right away. Watch for weakness, pale or yellow gums, and dark urine, which signal red blood cell damage.
Are garlic supplements safe for horses?
A clove in a commercial supplement is widely fed and generally tolerated. Do not add extra garlic on top of that, and avoid daily high doses. Ask your vet if you are unsure.
Careful for horses means: fine in a small amount, prepared as described, and not for every pet; the details say when to skip it.
General information from veterinary guidance, not a diagnosis. If you are worried, call your vet or a pet poison line: ASPCA Animal Poison Control (888) 426-4435. Charges may apply.
Written by Hoofdeck editors · updated Nov 13, 2026 · from ASPCA Animal Poison Control, Merck Veterinary Manual and university extension guidance.