AFLATOXINS

Toxin Characteristics

Aflatoxins, secondary metabolites produced by some strains of Aspergillus flavus and A. parasiticus, are the most commonly occurring mycotoxins in feedstuffs worldwide.

Aflatoxins are a group of highly toxic metabolites that includes specific forms designated as B1, B2, G1, G2, M1 and M2.

Aflatoxin B1 is the most commonly occurring type of aflatoxin and a potent cancer-causing agent.

It was once thought that aflatoxin formation only occurred during storage, but it is now well documented that aflatoxin production also occurs in the field prior to harvest.

Aflatoxin contamination in corn is usually associated with prolonged high day and night temperatures during the growing season and severe drought conditions during grain fill.

Crops and weather conditions

Aflatoxins can occur in several agricultural commodities including corn and other cereal grains, peanuts, cottonseed and other oil seed crops.

Aflatoxins are more common in grains from Southern regions and are rare in Northern areas of the U.S.

Field conditions conducive to A. flavus invasion of grains and subsequent production of aflatoxin are:

Daytime high temperatures of 90°F or greater.

Relative humidity of 80% or above.

Ear injury caused by insects, birds or hail, as well as drought stress, which predispose the crop to colonization by the fungus and aflatoxin contamination.

Rainfall at the end of the growing season that postpones harvest and prevents dry-down.

Storage conditions with corn moisture above 13% and moderate temperatures increase the risk of aflatoxin contamination.

Guidelines for Grain Use

Because of the carcinogenic properties of this mycotoxin, the Federal Drug Administration (FDA) has established the following guidelines:

The maximum allowable level of aflatoxin in feed grains for interstate commerce is 20 ppb.

The maximum level of aflatoxin in a complete feed should not exceed 100 ppb for within state use.

AFLATOXIN	ACTION LEVEL Concentration at which regulatory agencies will consider action
Milk	0.5 ppb
Food for human consumption	20 ppb
Corn grain intended for finishing beef cattle	300 ppb
Corn grain intended for finishing swine of 100 pounds or greater	200 ppb
Corn grain intended for breeding cattle, breeding swine and mature poultry	100 ppb
Corn grain and other animal feeds	20 ppb
Corn and other animal feed ingredients intended for dairy animals	20 ppb

Impact on Animal Health

Aflatoxicosis

Caution should be exercised when feeding contaminated rations to livestock or poultry.

There is considerable variation in tolerance to aflatoxins among the different animal species, for example:

Biological factors such as animal age and sex seem to play a role in the ability of the animal to tolerate aflatoxins.

The main target organ is the liver. High doses cause liver damage and hemorrhaging.

In general, young animals are more susceptible than adults.

Aflatoxins are not considered a serious threat to fertility, and are not likely to cause abortions at levels that cause moderate disease.

Cattle are more tolerant than swine.

Dairy farmers should not feed aflatoxin-contaminated feeds to lactating cows because the toxin will be transmitted into the milk.

The major economic impacts of aflatoxicosis in dairy herds are reduction in milk production and rejection of contaminated milk.

Beef cattle exhibit a failure to gain weight or a reduction in growth rate.

Swine show the clinical signs of aflatoxicosis as a decrease in feed conversion and a subsequent failure to gain weight.

Sheep are the most tolerant of all domestic animals.

Turkey poults and ducklings are extremely sensitive to aflatoxins.

Mature chickens are more tolerant than turkeys.