Because of weather conditions during the past growing season, mold and mycotoxin contamination of some crops, particularly corn, is common. Molds are organisms and mycotoxins are chemicals produced by certain species of molds that are toxic to animals. Visibly moldy grain may or may not have mycotoxins and mycotoxins can be found on feeds that are not visibly moldy. Moldy corn that is not contaminated with mycotoxins is not as nutritious as clean corn. Molds consume nutrients, usually the most digestible one, thereby reducing the nutrient content of the corn. Moldy corn typically has higher concentrations of fiber and lower concentrations of starch and fat than clean corn. If allowed, cattle will select against consuming visibly moldy hay and fiber digestibility can be reduced when cattle are fed visibly moldy silage. Experiments directly evaluating the effects of feeding moldy grain to dairy cows are lacking. The consensus among nutritionists is that moldy feed most likely will reduce feed intake, which will then result in reduced milk production.

Most of the research on moldy feeds have used hay or silage, and these typically comprise the majority of the diet. Corn and other grains usually make up less than one-third of the diet. Also because of all the mixing and blending that occurs during combining, storage, and feed manufacturing, mold is likely much less concentrated in grain than in hay or silage. This means that the increased amount of mold on corn grain this year may not be a general problem for cattle. However, if you observe visibly moldy corn (for example a moldy pocket in a bag) it should be discarded and not be fed to cows because of the potential decrease in intake and milk yield.

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