1998 Drought Information - Limit Feeding

Drought Brings Concern of Aflatoxin Contamination of Livestock Feeds to Oklahoma Dairy and Beef Producers

Dan N. Waldner, Ph.D.
OSU Extension Dairy Specialist

David L. Lalman, Ph.D.
OSU Extension Beef Cattle Specialist


Aflatoxins are a group of highly toxic compounds produced by the molds Aspergillus flavus, A. parasiticus and A. nomis which when ingested by livestock can result in increased disease and reduced production efficiency. Aflatoxins are known to exert their effects on livestock through three mechanisms: 1) alteration in nutrient content, absorption and metabolism, 2) changes in endocrine and neuroendocrine function, and 3) suppression of the immune system. The resulting symptoms mimic those of other metabolic and infectious diseases, including ketosis, Johne's, Bovine Viral Diarrhea, Salmonella and clostridial infections, and some poisonous weeds, making diagnosis difficult. To further complicate matters, molds may be growing actively without mycotoxin formation, and mycotoxins may be present even though mold growth is not readily evident. Therefore, appearance of the feed and presence of mold are also poor indicators of the potential for mycotoxicosis in livestock.

Aflatoxins can invade feedstuffs at any point from field to feedbunk. Although some feeds may be more prone to aflatoxin contamination, grains, by-product feeds, protein concentrates, finished feeds, oilseeds, food wastes and forages may become infected. The severity of aflatoxin contamination of feeds is determined by environmental factors such as excessive moisture in the field and in storage, temperature extremes, humidity, drought, and variations in harvesting practices and insect infestation. In the southern U.S., drought occurring during the latter part of the growing season appears to be the single most significant factor in crops where field infection has occurred.

Beside the negative effects on livestock production efficiency, aflatoxin contamination of feed is of particular concern to producers since it is a recognized carcinogen and major efforts are directed at eliminating its residue in food. The Food and Drug Administration is responsible for regulating aflatoxin levels in food and feed. Currently, with few exceptions, there is a limit of 20 ppb in food and feed products and 0.5 ppb in milk. It is advisable to contact the Oklahoma Department of Agriculture at (405) 521-3864 to receive current regulations governing the use of aflatoxin contaminated feeds consumed by livestock.

Feeding Aflatoxin Contaminated Feed to Dairy and Beef Cattle

Dairy Cattle: The maximum level for aflatoxin fed to dairy cattle is 20 ppb in the total ration dry matter. When lactating cows consume aflatoxin, it not only can be toxic to the cow but also appears in the milk within 24 hours. Generally, the levels of aflatoxin appearing in milk are 1 to 2 percent of the aflatoxin content of the feed. Lactating cows consuming feed containing 20 ppb or less of aflatoxin will have less than 0.1 ppb of aflatoxin in the milk. Violation of the 0.5-ppb limit will result in condemnation of the milk and additional milk cannot be sold until it has been tested and found free from aflatoxin. Research data indicate aflatoxins will clear the system of lactating dairy cows within 48 to 96 hours after the contaminated feed is removed from the ration.

Calves are much more susceptible than adult animals to the effects of aflatoxins. Therefore, their diets should be free (< 20 ppb) of aflatoxins. Since older heifers and dry cows are fed little grain, any aflatoxin associated with grain will be diluted greatly by the forage component of the ration. However, caution must be taken when feeding contaminated feeds with aflatoxin levels greater than 100 ppb to older heifers and pregnant animals since aflatoxin can cause prolapsed rectum, birth defects, and other reproductive failures. In general, it is recommended that no dairy animal receive rations containing aflatoxin levels greater than 20 ppb.

Beef Cattle: While it had been commonly assumed that beef cattle were more tolerant to aflatoxins than any other species of animals, it is clear that they are very sensitive and aflatoxin may increase stress susceptibility and compromise growth and efficiency. Calves are more susceptible than adults are, therefore young calves should not receive aflatoxin contaminated feeds nor should their dam, since aflatoxin can be passed in the milk. Additionally, cattle under stress (i.e., when starting young cattle on feed, shipping, during periods of extreme heat or cold, disease, nutritional deficiency, etc) should not be allowed access to contaminated feeds. It is also not advisable to give suspect feeds to pregnant animals for reasons mentioned previously. Older non-pregnant animals can tolerate contaminated feeds much better

Reduced growth and efficiency has been documented in cattle weighing less than 300 pounds receiving diets containing 150 to 200 ppb of aflatoxin in the total ration dry matter. Cattle weighing over 300 pounds have exhibited reduced growth and efficiency, as well as liver damage at aflatoxin concentrations greater than 220 ppb in the total ration dry matter. In general, potentially harmful effects may be witnessed in all classes of livestock at aflatoxin levels of 20 to 130 ppb in the total ration dry matter. The feeding of aflatoxin-free feeds to feedlot cattle is recommended for at least the last 3 weeks prior to slaughter.

Reducing the negative impact aflatoxin has on performance of livestock has been the subject of numerous research trials. Research indicates that the feeding of clays, such as sodium aluminosilicates and bentonites, can bind or adsorb some of the aflatoxin and prevent them from being absorbed from the animal's intestine. In addition, mannanoligosaccharides (MOS), which are derived from yeast cells, may be effective in reducing aflatoxin's toxic effects.

In general, the clay materials have been shown to bind 25 to 80 percent of the aflatoxin found in feeds when added to the ration at 0.5 to 1.0 percent of the total ration dry matter. Additionally, research indicates MOS may bind up to 80 percent of aflatoxins when fed at 0.125 percent of the total ration dry matter. However, due to variability in the ability of these compounds to bind aflatoxins, producers should not rely on these additives alone to fully restore performance and health or eliminate appearance of aflatoxin in milk. Additionally, neither the clays nor MOS are approved as anti-aflatoxin feed additives in the U.S.

The Bottom Line

The best advice to livestock producers is to not knowingly feed any feed ingredient containing aflatoxins. If homegrown ingredients are found to contain a low level of aflatoxin and it is economically imperative that this feed be used on the farm, then the decision to feed the ingredient should be based on: a) the contamination level; b) age and stage of production of the animals to receive the feed; and c) willingness to risk toxic effects in animals. Producers suspecting aflatoxin contamination of feed ingredients should contact the Oklahoma Animal Disease Diagnostic Laboratory at (405) 744-6623 for procedures on submitting samples for analysis.

Oklahoma Cooperative Extension Service
Division of Agricultural Sciences and Natural Resources
Oklahoma State University