Can they eat it? / Moldy hay and silage
Can horses eat moldy hay and silage?
No. Botulism, colic and lung disease.
Dusty, mouldy or heating hay causes heaves and colic; wet, poorly made haylage can carry botulism, which is often fatal. Open every bale and smell it; dump what is off.
Coughing (heaves); weakness, trouble swallowing, drooling (botulism); colic.
Call your vet now. Note what was eaten, how much and when; do not wait for signs.
Why it is dangerous
Mouldy hay and silage carry spores and toxins that irritate the airways and gut. Dusty or mouldy hay releases fungal spores that inflame the lungs and cause heaves, a chronic allergic airway disease. Wet, poorly fermented haylage can harbour Clostridium botulinum, whose neurotoxin blocks nerve signals to muscles and is often fatal. Moulds can also trigger colic through gut disruption.
How much is too much
For a 1,000 lb horse there is no safe amount of visibly mouldy, dusty or heating hay or haylage to feed, so a slice, a handful or a flake is already too much. The same holds for ponies, miniatures and metabolic horses, who may react sooner. If your horse has eaten any, treat it as a potential emergency and call your vet.
Horses
Horses in work or at pasture should never be fed hay or silage that is dusty, musty, warm to the touch or smells sour or rotten. Open every bale, smell it and check for white, grey or green fuzz. Dump anything off, and store hay dry and off the ground. Keep working horses away from dusty hay, since it strains the lungs during exertion.
Ponies and easy keepers
Ponies, miniatures, seniors and easy keepers are at higher risk from poor forage, and their guts and lungs can be more sensitive. Soak hay for a short period only if your vet advises it, and never feed hay that smells off. Watch closely for coughing, colic or weakness after a change in forage, and call your vet promptly rather than waiting.
Safe alternatives
Offer well-made, dry, green-smelling hay that has been tested or inspected, or a clean, properly fermented haylage from a reputable source. Hay pellets or cubes soaked to a damp mash are a dust-free option many owners use for horses with airway issues, after checking with your vet about soaking time and quantity.
Questions people ask
Can horses eat moldy hay in winter?
No. Mould grows in damp hay during winter storage. Check every bale and dump anything dusty, musty or fuzzy, even if the horse seems to want it.
My horse ate some moldy hay, what should I do?
Call your vet now. Note what was eaten, how much and when, and do not wait for signs such as coughing, colic or weakness.
Is moldy haylage a botulism risk?
It can be. Wet, poorly made haylage may carry botulism toxin, which is often fatal. Discard any haylage that smells rotten or was improperly wrapped or sealed.
Toxic for horses means: do not give it; if they ate it, call your vet or a poison line.
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.