Tracking Mycotoxins in Hay: Prevention & Testing Tips

How Mycotoxins End Up in Hay

Most mycotoxin problems in hay start with moisture. Hay that is baled before it has dried down, hay that gets rained on in the windrow, and bales that pick up water from a leaking roof or bare ground all give mold a place to grow. Once mold is active, some species can produce toxins, and those toxins stay in the forage even after the mold itself dries out or is hard to see.

Heat is the other warning sign. Bales that were put up too wet can warm up in the stack as microbes go to work. A bale that feels warm to the touch, smells sour or musty, or shows white, gray, or black dust when you break a flake is telling you something went wrong during curing or storage.

Grass hays can also carry toxins that start in the field, such as ergot, which shows up as dark, hard bodies in the seed heads of some grasses. Good field management and harvesting at the right stage help keep these out of the bale.

Why It Matters for Horses and Livestock

Horses are especially sensitive to moldy feed, and their digestive system gives them little room for error. Cattle, goats, sheep, and camelids handle some toxins differently, but none of them do well on contaminated forage over time. Depending on the toxin and how much an animal eats, problems can include:

• Refusing feed or eating noticeably less than usual
• Poor weight gain or a dull, rough coat
• Digestive upset and, in horses, a higher risk of colic
• Coughing or respiratory irritation from mold spores and dust
• Reproductive problems in pregnant mares, cows, and does
• A weaker immune system, so animals get sick more easily

Many of these signs can have other causes, so if an animal seems off, call your veterinarian and mention any recent change in hay.

How to Spot Risky Hay Before You Feed It

You cannot see mycotoxins, but you can catch the conditions that cause them. Before you feed from a new load, open a few bales from different parts of the stack and check:

• Smell: good hay smells fresh and slightly sweet. Musty, sour, or moldy odors are a red flag.
• Dust: shake a flake. A cloud of white or gray dust usually means mold spores.
• Color and texture: look for dark, clumped, or matted patches inside the bale, not just on the outside.
• Temperature: push your hand into the middle of the bale. Hay should feel cool, not warm.
• Weight: a bale that feels much heavier than the others may be holding moisture.

Testing Hay for Mycotoxins

If you are unsure about a load, especially for a pregnant mare, a senior horse, or a horse with a health condition, a forage lab can tell you for certain. Many forage testing labs offer mycotoxin screening alongside standard nutrient analysis. Use a hay probe to take core samples from 15 to 20 bales across the stack, combine them in a sealed bag, and send them in as one sample. Ask your veterinarian or extension office which panel makes sense for the animals you feed.

A standard nutrient test (protein, fiber, and relative feed value) does not check for mycotoxins, so ask for the mycotoxin screen specifically if that is your concern.

Preventing Mold and Mycotoxins in Storage

The best protection is buying well-cured hay and keeping it dry. At home, that means:

• Storing hay under a sound roof, out of rain and runoff
• Stacking bales on pallets so they never sit on bare dirt or concrete
• Leaving space between the stack and the walls so air can move
• Avoiding tarps sealed tight over bales, which trap condensation
• Feeding the oldest hay first and checking the stack regularly through the season

Our guide on preparing your barn for hay season walks through storage step by step.

When to Throw Hay Away

When in doubt, throw it out. Hay that is visibly moldy, smells musty, feels warm, or comes apart in dusty clumps is not worth the risk, especially for horses. Do not try to stretch it by mixing it with good hay. Pull damaged bales out of the stack, and check the bales around them, since moisture problems rarely stay in one spot.

Start With Clean, Well-Cured Hay

At Ohana Farms in Pasco, Eastern Washington’s dry summers help our alfalfa, timothy, and orchard grass cure properly before baling, and we store it under cover until it reaches your barn. See what’s in The Hay Barn, or contact us with questions about a load or how to store it.