Agricultural Division

Aflatoxin-infected Crops Threatens Drought Area in the Summer of 1998
Drought conditions are causing a new headache for farmers and ranchers in Southern Oklahoma and Texas ? the presence of aflatoxin-contaminated grain and other crops being produced in the region.

Aflatoxins are extremely poisonous to humans, livestock and poultry. However, because they are odorless, tasteless and have no color, they are difficult to detect. Corn is especially infected when stressed under such conditions as drought, but grain sorghum, peanuts and cotton also are at risk.

Jeff Ball, a soil fertility and crops specialist at the nonprofit Noble Foundation in Ardmore, Okla., said aflatoxins are poisonous byproducts from the soil-borne fungus Aspergillus, which is responsible for the decomposition of plant materials.

Aflatoxin consumption by livestock and poultry results in a disease called aflatoxicosis. All living organisms metabolize aflatoxins in the liver, but high concentrations can lead to acute liver disease or death within 72 hours. Lower aflatoxin concentrations result in various symptoms, including feed refusal, decreased feed efficiency, impaired reproduction, hemorrhaging in muscles, and suppression of the immune system.

"The amount of aflatoxin an animal can tolerate varies with age, sex and health," Ball said. "Younger animals are most susceptible to aflatoxin poisoning. Pregnant and growing animals have slightly more resistance, but less resistance than mature animals."

Accumulation of aflatoxins is dependent on weather conditions. A dry growing environment or drought stress tends to favor the development of aflatoxins in corn. When soil moisture is below normal and temperatures are high, the number of Aspergillus spores in the air increases. During pollination, these spores infect corn kernels either through silks (pollination tubes) or through areas of damage caused by insects, birds and weather events. Once infected, plant stress such as nutrient deficiency, continued dry weather or kernel damage during harvest may increase aflatoxin levels.

Drought conditions and the fear of aflatoxin contamination have resulted in grain in the region becoming more affordable. Economics appear to favor feeding grain through winter as an alternative to hay as a primary energy source. Although grain containing low levels of aflatoxin can be fed to livestock and poultry, risk is increased anytime aflatoxin is present at any concentration. If symptoms occur, discontinue feeding contaminated grain and return to an aflatoxin-free diet immediately.

There is not a procedure for eliminating aflatoxin after it is produced, but limiting or maintaining concentrations may allow contaminated grain to be fed under proper management. Irrigation has been shown to reduce the level of Aspergillus infection when applied during pollination. Also, harvesting corn early when moisture is above 20 percent and then quickly drying it to a moisture level of at least 15 percent will keep the Aspergillus fungus from completing its life cycle, resulting in lower alfatoxin concentrations. Ammoniating aflatoxin-contaminated grain stabilizes the level of concentration but does not eliminate the problem.

Feeding grain contaminated with any level of aflatoxin carries a considerable amount of risk, Ball said. Therefore, testing for aflatoxin concentrations should be the first step in proper feeding management.

The Noble Foundation crops specialist said the sampling technique used is the most important factor in determining aflatoxin levels. Sampling grain as it is moving or being blended, such as during harvest or loading, is best and will yield a representative sample. Obtaining a quality sample from stored grain is difficult since pockets of highly contaminated grain can exist. Ten to 15 probes yielding 1 pound of grain each should be obtained from different sites in the bin or truck and placed in a bucket. Mix the sample thoroughly and place a 10-pound sample in a paper bag or sack that can breathe. Then send the sample to a laboratory that conducts aflatoxin assays. Each truckload and bin should be sampled separately to achieve reliable results.

The use of a black light to detect the presence of aflatoxins at the elevator is common. However, this procedure is not reliable since it detects an acid and not the aflatoxin. It is recommended that a lab analysis be performed to accurately determine aflatoxin concentrations.

Recommended aflatoxin levels in feed is 0 parts per billion (ppb), but this is not always possible. If feeding contaminated grain to lactating dairy cattle, immature poultry or immature livestock, do not exceed 20 ppb aflatoxin in the total diet. Calves should not receive milk from cows fed more than 20 ppb aflatoxin. Breeding cattle, swine and mature poultry should not exceed 100 ppb in their total ration. Finishing beef cattle and swine can tolerate grain up to 300 ppb aflatoxin. Animals should not consume any level of aflatoxin in their diet for at least three weeks prior to slaughter. Any grain with levels exceeding 1,000 ppb should be destroyed and not be salvaged by blending with grain of lower concentrations.