Mouldy Hay and Horses: Why to Stop Feeding It
In this article
By Dr Duncan Houston
A musty bale is frustrating, especially when hay is expensive or difficult to replace. Feeding it to see whether your horse tolerates it is not a safe way to decide whether it is usable.
Stop using suspect hay, keep it separate from clean feed and arrange a safe replacement. If the horse is already coughing, uncomfortable or weak, involve your vet.
Quick Answer
Do not feed horses visibly mouldy, musty or spoiled hay. Dust and fungal spores can aggravate respiratory disease, and some contaminated feed may contain toxins that cannot be judged by sight. Soaking or steaming is not a dependable way to make spoiled hay safe. Remove the suspect batch and seek veterinary advice if the horse develops illness.
What makes mouldy hay a problem?
Fungal spores and other airborne particles can irritate a horse's airways. Some moulds can also produce mycotoxins under suitable conditions, but mould does not automatically mean a particular toxin is present.
The University of Minnesota's mouldy-hay guidance emphasises respiratory risks and explains that toxin-related illness can be difficult to confirm. A horse with cough or poor performance needs assessment rather than a diagnosis based only on the bale's appearance.
Botulism is a separate bacterial toxin problem, not another name for mould poisoning. Spoiled feed, inappropriate fermentation or carcass contamination can create additional hazards. Profound weakness or difficulty swallowing requires emergency veterinary assessment regardless of the suspected cause.
How should you assess a bale?
Inspect hay when buying, when opening each bale and before filling feeders. Look inside as well as at the surface. Watch for musty odour, damp patches, unusual discolouration, clumping, visible fungal growth or excessive dust.
Do not bury your face in a dusty bale to smell it. A clean-looking exterior cannot guarantee a clean centre, and a horse eating hay willingly does not prove that it is safe.
| Finding | Decision | Next step |
|---|---|---|
| Clean, suitable hay with no obvious spoilage | Continue normal quality checks | Store correctly and review nutritional suitability |
| Musty smell, mould, dampness or unexplained heavy dust | Withhold suspect hay | Separate the batch and obtain supplier or professional advice |
| Smoke, burning smell or dangerously heating stack | Possible fire emergency | Keep people and animals away and contact emergency services |
| Horse ill after eating suspect feed | Possible feed-related or unrelated disease | Contact the vet and retain batch information |
When is this an emergency?
Call your equine vet immediately for breathing difficulty at rest, severe colic, marked weakness, collapse or trouble swallowing. Do not wait to see whether removing the hay fixes these signs. If swallowing is abnormal, do not force water, feed or remedies into the mouth.
A persistent cough, reduced appetite, diarrhoea or unexplained poor performance also needs prompt advice. Fever, nasal discharge or several affected horses may suggest infection or a shared exposure, so tell the vet about the whole group.
What to do with suspect hay
- Stop feeding the suspect batch to every exposed horse.
- Provide an appropriate safe forage alternative and veterinary guidance if a major dietary change is unavoidable.
- Label and isolate the remaining bales so nobody uses them accidentally.
- Record supplier, delivery date, storage location and which horses received them.
- Ask your vet or forage laboratory how to collect a representative sample if testing is needed.
- Arrange disposal that prevents access by animals and follows local requirements.
Do not simply remove the visible patch or transfer the rejected hay to another species without professional advice. Contamination can be uneven, and a negative limited toxin panel does not certify every bale as safe.
Can soaking or steaming rescue it?
For otherwise suitable hay, specific dust-reduction methods may form part of an airway-management plan. That is different from rehabilitating spoiled feed. Wetting does not reliably remove mycotoxins, and home steaming may not treat the whole bale adequately.
If a horse needs low-dust forage, ask your vet or nutritionist to select a safe alternative and explain preparation, hygiene and nutritional implications.
Preventing storage problems
Proper hay selection and storage start with suitable harvest moisture and protection from water. Store off the ground in a weatherproof, ventilated space, inspect leaks and rotate stock so older suitable hay is used first.
Newly stored damp hay can heat dangerously. Follow professional hay-fire guidance for monitoring. Never climb into or disturb a suspected burning stack to investigate; moving it can expose hot material to oxygen and put people at risk.
Common mistakes
- Offering a small feeding trial to test safety.
- Assuming only the visibly mouldy section is affected.
- Using soaking, steaming or supplements as permission to feed spoiled hay.
- Storing rejected bales where another worker may use them.
Frequently asked questions
Can mouldy hay harm a horse without being eaten?
Yes. Airborne dust and spores can affect airways, including during handling nearby.
Does all mould produce toxins?
No, but visual inspection cannot identify every toxin risk. Spoiled hay remains unsuitable.
Should I save a sample?
Yes, if advised by your vet or laboratory. Keep its batch details and avoid further exposure while collecting it.
Rejecting a bale can feel wasteful, but the safer decision is clear: replace suspect forage and investigate illness early.
For support with feed-quality and ongoing care questions, visit ASK A VET™. Serious signs need an equine vet immediately.
