Moldy Feed and Spoiled Food Risks for Cows

Moldy or spoiled feed is a real health concern for cows. The problem is not only the mold you can see. Some fungi produce mycotoxins, and those toxins can remain in feed even when the mold is no longer obvious. Wet hay, poorly fermented silage, damaged corn, caked concentrates, and spoiled bakery or produce waste can all create risk. Decaying plant material or hidden carcass contamination in spoiled forage can also raise concern for botulism.

Cattle can break down some toxins better than monogastric animals because of the rumen, but that protection is incomplete. Dairy cows, calves before the rumen is fully functional, pregnant cattle, and animals under stress may be more vulnerable. Common consequences include lower feed intake, reduced weight gain, milk loss, diarrhea, liver injury, reproductive problems, and in severe cases sudden illness or death.

Aflatoxins are especially important in dairy cattle because contaminated feed can lead to aflatoxin M1 residues in milk. FDA action levels are strict for dairy animals and immature animals. Other toxins such as deoxynivalenol (DON or vomitoxin), zearalenone, and fumonisins may also affect cattle, depending on the feed source and contamination level.

If feed smells rotten, feels hot, looks heavily moldy, has obvious caking, or contains foreign material, it is safest to stop feeding it and contact your vet or nutrition team. Saving a sample of the suspect feed in a clean bag can help with testing and herd decisions.

There is no reliable at-home safe amount of visibly moldy or spoiled feed for cows. A small amount may cause no obvious signs in one animal and serious illness in another. Risk depends on the toxin involved, the amount eaten, the type of feed, and whether the cow is a calf, pregnant, lactating, or already stressed.

For aflatoxin, FDA action levels are 20 ppb for feed intended for dairy animals and immature animals, 100 ppb for breeding beef cattle, and 300 ppb for finishing beef cattle feed. For fumonisins, FDA guidance lists 10 ppm total fumonisins for all other species or classes of livestock, including lactating dairy cattle. Merck notes that ruminants often tolerate DON better than pigs, and adult cattle may consume around 10 ppm dietary DON without obvious feed refusal in some situations, but that is not a recommendation to feed moldy grain.

Visible spoilage still matters even when a lab value is unknown. Moldy pockets in hay or silage are often nutritionally poor, less digestible, and unevenly contaminated. That means one mouthful may be low risk while the next is not. Because contamination is patchy, mixing spoiled feed into a ration can spread the problem rather than solve it.

The safest practical rule is this: if feed is clearly moldy, rotten, slimy, foul-smelling, heating, or contaminated, do not assume dilution makes it safe. Ask your vet and nutritionist whether the feed should be discarded, tested, or redirected away from higher-risk animals.

Cows exposed to moldy or spoiled feed may show vague signs at first. You might notice lower appetite, sorting feed, reduced cud chewing, a drop in milk production, loose manure, or slower growth. In some herds, the first clue is not dramatic illness but a quiet decline in performance.

More concerning signs include dehydration, weakness, tremors, poor coordination, jaundice, photosensitivity, abortions, infertility, swollen vulva in heifers, or several animals becoming ill after a ration change. Spoiled silage or decaying feed contaminated with botulinum toxin can cause progressive weakness, trouble swallowing, and recumbency.

See your vet immediately if a cow has sudden neurologic signs, cannot stand, stops eating completely, shows severe diarrhea, has marked abdominal pain, develops yellow gums or eyes, aborts, or if multiple cattle are affected at the same time. Herd outbreaks can move quickly, and early feed removal plus supportive care may limit losses.

When you call, be ready to share what changed, when the feed was opened or delivered, which group ate it, and whether you can save a representative sample. Photos of the feed face, bunk, bale, or storage area can also help your vet assess the situation.

Safer feeding starts with clean, well-stored forage and grain. Offer dry hay that smells fresh, silage with normal fermentation odor and no obvious spoilage pockets, and concentrates that are not caked, damp, or insect-damaged. Rotate inventory, protect feed from rain and groundwater, repair torn plastic on wrapped bales, and keep bunks and commodity bays clean.

If you are trying to stretch feed supplies, talk with your vet and a qualified cattle nutritionist before using borderline feed. Options may include testing suspect lots, feeding only lower-risk groups if your team says it is appropriate, reformulating the ration with cleaner ingredients, or replacing spoiled forage with sound hay, haylage, corn silage, or a balanced commercial ration.

Some farms also discuss toxin binders or adsorbents with their veterinary and nutrition teams. These products may help in selected situations, but they do not make rotten feed safe and they do not replace proper storage, testing, or feed removal. FDA notes it has not licensed a product for use as a mycotoxin binder in animal feeds.

If you are unsure whether a feed is usable, the most practical next step is to stop feeding that batch, isolate it, and ask your vet what level of testing and ration adjustment fits your herd. Conservative decisions early often prevent larger medical and production losses later.