I have a good source for hay and in the fall we had them put aside about 5 tons of hay to get us through the winter. In all that hay, I found just one moldy bale.

You should never feed moldy hay. Breathing in mold spores can cause a horse to develop Chronic Obstructive Pulmonary Disease (COPD).

How can you tell if hay is moldy?

Often you can’t tell a bale will be moldy until you open it up. At that point, it becomes more obvious.

• Moldy hay is usually very compressed and heavy.
• When you break the bale apart it the hay will look black and stiff, not green and leafy.
• Often you an see the mold spores (like on the hay to the left) which are gray and powdery.
• Moldy hay will often emit a plume of mold dust when you open the bale.
• Moldy hay smells musty.

What causes mold to form?

In a bale of hay mold appears if the hay is baled while it’s still damp. After cutting, hay must stay on the ground long enough to “cure” (around three days), but there’s a balance — the longer it sits in the field, the more the sun bleaches nutrients out of it. So the farmer must bale the hay as soon as it’s dry enough. If there’s any rain, the hay must be dried longer and possibly fluffed up to expose it the sun.

You can cause mold to form if you put a plastic tarp over bales to protect it from rain. If the hay is still curing, the tarp prevents moisture from escaping.

Damp hay is a fire hazard

In addition to causing hay to become moldy, moisture can can also cause baled hay to generate heat. A barn full of damp, hot bales is a real fire hazard because the bales can spontaneously combust.

That’s why it’s important to buy your hay from suppliers you trust and to store it properly.