Aflatoxins are mycotoxins of major concern to the dairy industry. Most mycotoxins are found in grain, usually grown in a drought, although they may contaminate pasture grass and occasionally hay. Most frequently, aflatoxins are found in corn and cottonseed, and sometimes in their byproducts, but also on rare occasions in soybeans or distiller's grain. Peanut products also may be contaminated with aflatoxins and can result in aflatoxins in milk.
Because aflatoxins are carcinogenic to animals and perhaps humans, they are monitored closely in the food supply. Aflatoxins are the most carcinogenic natural compounds known. Milk that is sold commercially is checked for aflatoxin M1. When aflatoxin M1 is found at concentrations of 0.5 parts per billion (ppb) or greater, the milk is discarded because it cannot be used for products that go into the human food supply. On occasion, milk processors may also use a level less than the 0.5 parts per billion or 500 parts per trillion as a guideline for allowing milk into the human food supply.
Lactating cows that eat feed containing 20 ppb or greater aflatoxins may produce milk that exceeds the tolerance level for aflatoxins in milk. It usually takes the cow approximately two to three days on aflatoxin-free feed for milk concentrations to fall below tolerance levels. The length of time required for milk to become aflatoxin free is dependent on the concentration of aflatoxins in the feed (and milk) as well as the diet being fed to the cow.
Mycotoxin production is found most frequently in pre-harvest grains that are harvested under high temperatures, prolonged drought and high insect activity. Thus, aflatoxin contamination in grain is much greater in states such as Arkansas which have warm temperatures and high humidity. Corn and cottonseed should be screened for aflatoxin if there is a likelihood of contamination. Generally, all corn processed at a feed mill or mixed in a total mixed ration for milking dairy cattle should be scanned with a black light for aflatoxins.
If aflatoxin M1 is detected in milk, the grain that is being fed to milking cows should be replaced with aflatoxin-free grain that contains bentonite and/or a commercially available dietary chemisorbent. An exception would be if the cows have been milked following the pickup on the contaminated milk; then the milk should be tested to determine the level of aflatoxin. If the milk is above 0.5 ppb aflatoxin, the grain should be replaced; if the milk is below 0.5 ppb aflatoxin or has declined markedly, one might not replace the feed if it is likely future milk will be acceptable. In all cases, the grains should be tested for levels of aflatoxin.
Records should be maintained for all feeds, feeding practices, milk contamination and animal health and performance for all cases of aflatoxin contamination of milk.
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Article made possible through the contribution of University of Arkansas Cooperative Extension Service.