Will horses eat moldy hay? They will if they are hungry or if the mold is hidden, but this behavior creates a serious health risk. While horses often use their sense of smell to avoid spoiled forage, they cannot always detect toxins trapped inside tightly packed bales. Feeding this material can cause respiratory issues, colic, or poisoning, so it is safer to discard decaying hay rather than relying on the horse to reject it.
Quick facts about moldy forage
Discard any bale that smells musty, sour, or like vinegar, as these are primary indicators of fungal growth. If you detect these odors, assume the entire bale is compromised.
Check the center of the bale for heat. If the core feels warm to the touch, active decomposition is underway. This heat signals the presence of harmful bacteria that can cause respiratory distress in livestock.
Look for white, gray, or blue-green dust that puffs out when you break open a flake. These clouds are concentrated fungal spores. Inhaling these spores can trigger immediate allergic reactions in horses or cattle.
Store all hay in a dry, well-ventilated area with a pallet base to prevent moisture from wicking up from the ground. Aim for at least four inches of clearance between the hay and the floor.
If you find mold, don’t attempt to wash or dry the hay. The spores and toxins remain even after the visible mold is gone. Feeding this forage carries a high risk of colic or long-term liver damage.
This advice assumes standard grass or legume hay. If you’re feeding specialized forage, check the specific moisture guidelines provided by the supplier.
Will horses eat moldy hay and why it’s dangerous
The primary danger of feeding moldy hay lies in the production of mycotoxins, which are poisonous compounds created by fungi during the decomposition process. When a horse consumes these toxins, they can suffer from acute liver damage, neurological impairment, or chronic digestive upset. Because horses have a highly sensitive gastrointestinal tract, even a small amount of contaminated material can trigger severe colic or laminitis, both of which are life-threatening conditions.
Beyond the toxins, the physical presence of mold spores poses a significant threat to the horse’s respiratory system. When a horse inhales these spores, it often leads to Recurrent Airway Obstruction, commonly known as heaves. This condition causes chronic inflammation of the small airways in the lungs, making it difficult for the horse to breathe during exercise or even while resting. According to the University of Minnesota Extension, horses can develop permanent lung damage after long-term exposure to dust and mold spores found in poor-quality forage.
A common mistake owners make is assuming that removing the visibly dusty flakes makes the rest of the bale safe. In reality, mold mycelia often permeate the entire bale, meaning the internal moisture content is likely too high throughout. If a bale feels warm to the touch or has a damp, heavy weight compared to others, it’s actively composting. This heat indicates an ongoing microbial process that creates a breeding ground for bacteria like Clostridium botulinum.
Furthermore, the nutritional value of moldy hay is severely compromised. The fungi consume the plant’s sugars and proteins, leaving behind a product that provides little energy and often lacks the necessary fiber for healthy digestion. If you notice a change in the color or texture of your hay, you must assume it has lost its nutritional integrity. If you’re unsure whether a bale is safe, the best practice is to perform a visual and olfactory inspection of every flake. If you see clumping, dark patches, or smell anything other than fresh, sweet grass, don’t feed it to your animals. This decision rule is simple: if the hay looks or smells wrong, it isn’t worth the risk of a high veterinary bill or the loss of the horse.
When the quality of forage changes
| Situation | What changes | What to do instead |
|---|---|---|
| High humidity | Mold grows faster | Increase airflow immediately |
| Discolored patches | Nutrient loss occurs | Remove spoiled sections |
The most common mistake is assuming that removing a small, visible patch of mold makes the rest of the bale safe. In reality, fungal hyphae often penetrate deep into the forage long before discoloration appears. If you find a clump, assume the contamination has traveled at least six inches into the surrounding material.
Use this decision rule to protect your livestock: if the forage feels warm to the touch, internal fermentation has already compromised the nutritional profile. In this case, don’t attempt to salvage any portion of the bale. Feeding heat-damaged forage often leads to reduced protein absorption and can trigger respiratory distress in sensitive animals. When in doubt, prioritize the health of your herd over the cost of the feed. Discarding one bale is always cheaper than treating a sick animal.
How to properly inspect and store hay
Inspect each bale upon delivery by checking the exterior for signs of moisture, such as dark stains or soft spots. These indicate the hay was baled above the safe 15% moisture threshold. If the bale feels heavy for its size or warm to the touch, reject it immediately to avoid the risk of spontaneous combustion.
Store your hay in a barn or shed that stays at least six inches off the ground. Use wooden pallets to ensure air moves underneath the entire stack. This airflow prevents the bottom layer from wicking up ground moisture, which is the most common cause of rot in otherwise healthy crops.
Maintain a gap of at least one foot between the walls and the hay stacks. This prevents condensation from forming on the outer layers during temperature swings.
Remove the twine or wire from a new bale and fan out the first few flakes to check for hidden pockets of white or green dust. If you see fine, spiderweb-like filaments, don’t feed it. These are fungal mycelia, which indicate the presence of mold and potential toxins.
Smell the center of the bale. It should have a pleasant, earthy scent. It should never smell sour, like vinegar, or like rotten compost. If you find any signs of mold, remove the entire bale from the stable area immediately to prevent the spread of spores to other stored feed.
The mistakes that ruin your feed
Leaving hay sitting directly on a concrete floor allows moisture to rise, which creates the perfect environment for mold to thrive. Always use pallets or rubber mats to create a four-inch air gap beneath the stack.
Buying hay baled with too much moisture causes internal heating, which destroys nutritional quality within weeks. If a bale feels warm to the touch or has a bleached, dusty appearance, it has likely already undergone this process.
Ignoring a musty smell in the barn often means mold is present in the air. This can cause permanent respiratory damage to your horses, even if the hay looks clean. If you detect this scent, move the entire supply to a well-ventilated area immediately.
Trying to save money by feeding the least moldy parts of a bale is a dangerous mistake. Toxins are often invisible and spread throughout the entire flake. If you find a patch of mold, discard the whole bale to avoid colic or systemic illness.
Frequently asked questions
Can I feed moldy hay if I soak it first?
No, soaking moldy hay doesn’t make it safe for horses. Soaking can’t remove mycotoxins or kill fungal spores embedded in the plant fibers. You must discard any hay showing signs of mold, as it can’t be treated.
How long does it take for mold to grow in hay?
Mold can grow in 24 to 48 hours if hay moisture exceeds 15 percent. If hay feels warm or damp, you must improve airflow to prevent rapid fungal development. Checking moisture levels upon delivery is the best way to ensure safety.
Is it safe to feed dusty hay if it isn’t moldy?
Dusty hay isn’t always safe, as it often contains fungal spores that irritate a horse’s lungs. You can mist dusty hay with water to reduce airborne particles, but you must feed it immediately to prevent new mold growth.
What happens if my horse eats a small amount of moldy hay?
A horse may show no immediate symptoms after eating moldy hay, but the risk of colic or respiratory inflammation remains. If your horse consumes a significant amount, contact your veterinarian immediately to monitor for signs of illness or poisoning.
Does the type of hay affect mold growth?
Yes, the type and density of hay significantly affect how quickly mold grows. Legume hays are denser than grass hays, making them harder to dry and more prone to trapping moisture. Always inspect the center of dense bales for hidden mold.
How do I know if my hay has too much moisture?
You can check moisture content using a professional hay moisture tester. For safe storage, moisture levels should remain below 15 percent, as anything above 18 percent risks mold growth and spontaneous combustion. If you lack a tester, avoid bales that feel heavy or damp.
Horses eat, in short
Keeping your hay dry and free from contaminants is the single best way to ensure your horses stay healthy throughout the winter. By following a strict inspection routine when you receive and feed each bale, you protect your animals from the hidden dangers of mycotoxins and respiratory irritants. Always prioritize quality over cost when selecting forage, as the price of healthy hay is far lower than the cost of treating a sick horse.