Recent weather conditions are right for the opportunistic growth of fungi, Aspergillus flavus and Aspergillus parasiticus, which produce toxic metabolites, aflatoxins, in drought-stressed corn under appropriate environmental conditions.

Aflatoxins have been shown to be carcinogenic in laboratory animals. Because of the risk of aflatoxins being excreted in milk, the FDA has set the action level for total aflatoxins at 20 ppb for foods, such as corn, which are to be fed to dairy cows. The action level for aflatoxins in milk has been set at 0.5 ppb.

Livestock producers buying this year’s corn will want to check for the presence of aflatoxins before feeding this corn to cattle, especially lactating dairy cows.

Several methods exist for checking for the presence of aflatoxins:

1. Screening with a black light: A sample of corn is cracked and placed under the black light. A by-product of Aspergillus flavus, kojic acid is produced under the same growth conditions as aflatoxins. Under UV light kojic acid gives off a yellowish-green fluorescence. This screening suggests indirectly that aflatoxins are present. A quantitative test needs to be run to determine if the level is of concern when fed to livestock.

2. Other tests include ELISA and thin-layer chromatography.

3. Samples can be tested for aflatoxins at the Veterinary Medical Diagnostic Laboratory at the College of Veterinary Medicine, PO Box 6023, Columbia, MO 65205

Samples should represent a sampling from at least 5 locations of the bin and be pooled. As an alternative, grain can be collected periodically over 15 to 30 minutes from a moving stream as the grain is emptied from a storage bin. A sample size of one pint can then be submitted for analysis. Dr. Rottinghaus suggests to do the screening first (TLC at $20.50; the quantitative test is $36.00 if needed.

FDA guidance levels for aflatoxins in feedstuffs fed to various classes of livestock are:

1. Feed for dairy cattle and immature animals should contain less than 20ppb.
2. Feed with less than 100ppb can be fed to breeding cattle, breeding swine
and mature poultry.
3. Feed with less than 200ppb can be fed to finishing swine.
4. Feed with less than 300ppb can be fed to finishing cattle.

It is also possible to find aflatoxins in corn silage. Do not feed moldy corn silage. Proper ensiling (65-67% moisture) reduces the production of aflatoxins during storage. Corn silage should be covered immediately after filling with heavy plastic (5-6 mil). Sides should be sealed with dirt or sand and top covered well with tires (tire against tire).

If aflatoxins are suspected, a one quart sample of silage should be submitted to the lab for quantitative analysis.

For producers, especially dairymen, who are concerned about violative concentrations of aflatoxins in their feed, an additive, hydrated sodium calcium aluminosilicate (HSCAS), can be mixed with the feed in question to partially tie up the aflatoxins. Be sure to consult with a nutritionist and/or veterinarian.

by Dr. Barry Steevens, Dr. George Rottinghaus and Dr. Tim Evans