The majority of these molds are found naturally in soil. Normal growing conditions usually prevent the molds from producing high amounts of mycotoxins in grain and silage crops. During unfavorable growing conditions, such as drought or very wet conditions, or improper storage of feeds, mold spores are allowed to germinate and reproduce in large numbers, producing high levels of mycotoxins. Aflatoxin is the most studied and most widely known mycotoxin. It is produced by strains of Aspergillus which can be found all over the world.
Calves are more susceptible to the effects of aflatoxin than adult cattle.
Aflatoxins reduce animals performance and overall health. While pigs and other animals seem to be sensitive to DON, there is controversy as to is effects on dairy cattle. It has been reported by some researchers to reduce feed intake and milk production while others have concluded that DON causes no ill effects even at high doses. The presence of DON in feed is often used as a marker for the presence of other mycotoxins in the feed which are more difficult to detect but have more of a toxic effect on dairy cattle. Cows suffering from T-2 toxicity show signs of gastroenteritis and intestinal hemorrhages.