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Feeding moldy grain to cattle

Quick facts

  • Mold can grow on grain in the field, storage or feed bunk.

  • Molds and mycotoxins can harm cattle and lower the nutritional value of feeds.

  • The three common molds that produce mycotoxins and grow on grain are Aspergillus sp, Fusarium sp and Penicillium sp.

  • Grains should have less than 10 parts per million of vomitoxin for ruminating beef cattle and feedlot cattle over 4 months old. These grains shouldn’t make up more than 50 percent of the diet.

Health problems

Moldy grain can harm cattle production due to the following nutrition effects.

  • Mycoses: a disease state caused by the mold itself.
  • Mycotoxicoses: a disease state caused by a toxin (mycotoxin) produced by the mold.

Mycoses can occur in both animals and humans. Mold spores can cause respiratory distress in humans. People handling very moldy grain should wear masks to prevent sneezing, coughing and shortness of breath. These problems may occur from breathing in mold spores or having allergic reactions.

Respiratory problems aren’t clearly reported in cattle. But you should consider them when cattle have reduced dry matter intake or breathing problems from feed. Molds rarely cause systemic disease, but have caused abortion and blood poisoning in cattle.

The mold itself may cause production losses separate and apart from any toxin effects. Consider the potential effect of grains with greater than 1 million mold cfu/g on the following.

  • Lungs
  • Rumen fermentation
  • Reproductive function
  • Nutrient intake
  • Production

Mycotoxin effects


Feedlot cattle may consume diets containing up to 18 milligrams of vomitoxin per kilogram of dry matter without harm. Research is underway to evaluate if vomitoxin content creates a food residue concern. Research results should permit grain producers facing vomitoxin problems to seek others ways to market their grains as animal feed.

F-2 toxin

Growing heifers to first breeding shouldn’t consume more than 5 milligrams of F-2 toxin per kilogram of diet dry matter. Heifers fed 250 milligrams of F-2 toxin per day had reduced ovulation rates.

Cows may be more resistant to F-2 toxin toxicosis than heifers.

Managing mycotoxins

Grain or grain byproducts used in rations for ruminating beef cattle and feedlot cattle over 4 months old shouldn’t go above 10 parts per million of vomitoxin. These ingredients shouldn’t make up more than 50 percent of their diet.


Mold lowers the nutritional value of feed

Most livestock feeds have mold spores on them. Spore counts less than 10,000 colony forming units per gram (cfu/g) are common for grain. You can see mold when spore counts reach about 1,000,000 cfu/g.

In the field or storage, molds use the grain’s nutrients for growth. As a result, the grain’s nutritional value decreases.

  • Energy, crude protein and crude fat values of moldy corn declined 5, 7 and 63 percent, respectively in Summers and Leeson’s study.

  • Dietary fat declined 37 to 40 percent after 25 days and 52 to 57 percent after 50 days of storage according to Bartov 1985.

Besides nutritional value, animal production may decline after eating moldy feed. Many molds produce substances with antibiotic activity, which can alter rumen microflora if eaten by cattle. Thus, you can discount the nutrient value of grain by 5 to 10 percent if it has 1 to 5 million cfu/g.

Common molds in feedstuffs

Not all molds produce mycotoxins. Molds that produce toxins are toxigenic molds. Both toxigenic and nontoxigenic molds can relate to mycoses in cattle.

Common toxigenic molds found in grains and forages in the Upper Midwest include:

  • Aspergillus sp

  • Fusarium sp

  • Penicillium sp

Common nontoxigenic molds include:

  • Absidia sp

  • Acromoniella sp

  • Alternaria sp

  • Cephalosporium sp

  • Chaetomium sp

  • Cladosporium sp

  • Epicoccum sp

  • Helminthosporium sp

  • Mucor sp

  • Nigrospora sp

  • Phoma sp

  • Scopulariopsis sp

  • Trichoderma sp

Aspergillus sp

Aspergillus sp produces the mycotoxin aflatoxin.

Aflatoxin seldom occurs in grains in the Midwest. Aflatoxin production occurs in corn during drought settings. But, aflatoxin may affect Upper Midwest cattle producers any year if they purchase cotton or peanut seed products.

Fusarium sp

Fusarium sp produces the mycotoxins vomitoxin and F-2 toxin. Vomitoxin is less toxic than F-2 toxin at the same levels.

Fusarium sp molds cause head blight in small grains and stalk rot in corn. Fusarium graminearum causes head or kernel blight in wheat or barley. We commonly refer to this disease as scab in both grains. Scab usually occurs when the mold spores in the grain’s flower and grows after rainfall.

F-2 toxin has caused estrogenic effects in many laboratory and domesticated animals. You can measure mycotoxin impact on animal production in terms of production costs and food safety. Ingesting vomitoxin can be harmful to animals and humans.


Mold growth relates to grain variety, temperature and moisture. Fusarium sp grows in Upper Midwest fields when the weather is wet and cool.

  • Temperatures of 70 F or less

  • Relative humidity over 70 percent

The prevalence and severity of Fusarium growth relate to the number of rainy days when the grain is blooming.

Penicillium sp

Penicillium sp produces the mycotoxins penicillic acid and patulin.

Penicillic acid and patulin haven’t related harmful health effects in cattle in the Upper Midwest.

Mold growth

Molds need the following to grow.

  • Moisture, relative humidity over 70 percent

  • Oxygen, minimum 1 to 2 percent O2

  • Time

  • An ideal temperature for certain species

    • High temperatures promote Aspergillus

    • Low temperatures promote Fusarium

Mold can grow on grain in the field, storage or feed bunk.

  • Weather can affect mold growth in the field.

  • Keep grains dry to prevent mold growth in storage.

  • Molds that infest crops in the field may differ from molds that grow in storage or the feed bunk.

Alfredo DiCostanzo, Extension animal scientist and Michael Murphy, former professor, College of Veterinary Medicine

Reviewed in 2021

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