Mycotoxicosis in Ox: Mold Toxin Poisoning in Cattle

Mycotoxicosis is poisoning caused by mycotoxins, which are toxic compounds produced by certain molds growing on feed ingredients, stored grain, hay, haylage, silage, or pasture plants. In cattle, the problem is often linked to contaminated corn, small grains, cottonseed products, wet or poorly stored forage, or ergot-contaminated seed heads. The mold itself may or may not be obvious, and feed that looks acceptable can still contain harmful toxin levels.

Cattle can be exposed to several different toxins, including aflatoxins, trichothecenes such as deoxynivalenol (DON), zearalenone, fumonisins, and ergot alkaloids. Signs vary with the toxin, dose, and length of exposure. Some cattle develop vague herd-level problems like lower intake, reduced gain, rough hair coat, poor fertility, or milk drop. Others develop more serious illness, including liver damage, bleeding problems, abortions, heat intolerance, lameness, or tissue death at the tail or ears.

Ruminants are sometimes less sensitive than monogastric animals because the rumen can partially detoxify some compounds. That said, calves, pregnant animals, stressed cattle, and dairy cattle can still be significantly affected. Chronic low-level exposure is especially frustrating because it may look like a nutrition, reproduction, or management problem rather than a toxin issue.

For pet parents and producers, the key point is this: mycotoxicosis is usually a feed and herd health problem, not a contagious disease. Early recognition, feed removal, and a practical plan with your vet can limit losses.

Mycotoxicosis happens when cattle eat feed contaminated with toxins produced by molds such as Aspergillus, Fusarium, and Claviceps. Contamination can begin in the field during drought, plant stress, insect damage, flooding, delayed harvest, or humid weather. It can also worsen in storage if grain or forage is put up too wet, packed poorly, exposed to oxygen, or allowed to heat and spoil.

Common risk feeds include corn, small grains, cottonseed products, hay, haylage, baleage, and silage. Aflatoxins are classically associated with Aspergillus in corn and other feedstuffs, especially under hot, dry stress followed by poor storage. Fusarium toxins such as DON and zearalenone are more often linked to cool, wet crop conditions. Ergot alkaloids come from ergotized grains or grasses and can cause blood vessel constriction, lameness, and tissue necrosis.

One challenge is that visible mold does not reliably predict toxin level. Some badly molded feed has little measurable toxin, while normal-looking feed may test high. Mixed contamination is also common, and several toxins together may cause broader or more severe clinical effects than one toxin alone.

Cattle factors matter too. Calves, pregnant cattle, lactating dairy cattle, and nutritionally stressed animals may be more vulnerable. Dairy herds need special caution because aflatoxin B1 in feed can be converted to aflatoxin M1 and excreted in milk, creating both animal health and food safety concerns.

Diagnosis usually starts with a careful history and ration review. Your vet will want to know when signs started, whether there was a new load of feed, which groups are affected, and whether the problem is tied to one bunk, silo face, bale lot, or grain source. Because signs can be vague, mycotoxicosis is often a diagnosis made by combining herd patterns with feed evidence and ruling out other diseases.

A physical exam and basic herd workup may include bloodwork, liver enzyme testing, clotting assessment, pregnancy evaluation, milk production review, and sometimes necropsy if an animal dies. These tests do not prove every toxin, but they can show organ injury and help your vet narrow the list. Liver changes, poor coagulation, reproductive disruption, and distal limb damage can all support suspicion depending on the toxin involved.

The most useful next step is often representative feed sampling for laboratory analysis. That means sampling the actual suspect feed correctly, because toxin levels can be unevenly distributed. Your vet or diagnostic lab may recommend testing for aflatoxin, DON, zearalenone, fumonisins, or ergot alkaloids based on the ration and clinical signs.

Diagnosis can take time, and there is not always a single perfect test. In many cases, the strongest evidence is a combination of compatible signs, toxin detected in feed, and improvement after the suspect feed is removed or diluted under veterinary guidance.

Prevention starts with feed management before cattle ever eat the ration. Harvest crops at the right maturity, avoid unnecessary plant stress when possible, dry grain properly, and store feed to limit moisture, heating, and oxygen exposure. For silage and haylage, good packing, sealing, fermentation, and face management matter. Wet pockets, spoiled edges, and heating areas deserve extra attention.

Inspect feed regularly for musty odor, caking, heating, discoloration, clumps, or visible spoilage, but remember that toxins may be present even when mold is not obvious. If a load of grain, a bale lot, or a silo face seems questionable, pause before feeding it widely. Testing is especially helpful after drought, flooding, delayed harvest, or known regional mold pressure.

Work with your vet and nutritionist to protect the most vulnerable groups. Calves, breeding cattle, pregnant animals, and lactating dairy cattle should not be the first group exposed to questionable feed. In dairy operations, aflatoxin prevention is especially important because contaminated feed can lead to aflatoxin M1 in milk.

A practical prevention plan often includes routine feed sourcing standards, storage checks, strategic testing, bunk hygiene, and rapid removal of spoiled feed. Some herds also use toxin binders in higher-risk periods, but these products should support, not replace, good feed management. The safest long-term strategy is to reduce contamination risk at harvest, storage, and feeding.