April's Ag Advice by April Borders If we thought that we were out of the woods from the drought we need to stop and guess again. The latest issue that we need to deal with is aflatoxin. Aflatoxin is primarily a problem in corn but can also occur in other grain crops. Aflatoxins are produced from a fungus and grow as mold on stored grain. They are highly toxic to livestock, poultry, and people.
The development of aflatoxins depends on the infestation and growth of the Aspergillus mold in grain. Below normal soil moisture (drought stress) has been found to increase the number of Aspergillus spores in the air. Therefore, when drought stress occurs during pollination, the increased inoculum load (spores in the air) greatly increases the chance of infection. Furthermore, drought stress, nitrogen stress, and other stresses that affect plant growth during pollination can increase the level of aflatoxins produced by Aspergillus fungi. Often, Aspergillus will grow on the unfilled portions of the ear.
Dr. Marty Draper, Extension plant pathologist at SDSU, has received reports that a couple of loads of corn grain in southeast South Dakota and Nebraska have been rejected for aflatoxin. In the past, elevator operators and buyers used the black light test, but this test simply detects compounds that fluoresce (aflatoxins and others) and should only be used to select samples that require further testing.
Aflatoxin is one of the biochemical agents that will emit a blue-green glow under a "black light." It is not the only cause of fluorescence under UV light. It is important to note that fluorescence under UV light is not a definite test for aflatoxin, it is a presumptive test.
Grain loads that test positive for fluorescence should be probed and sent to an accredited lab for confirmation of mycotoxin. Similarly, minicolumn tests are no longer recommended, as they were prone to give false positive results if used improperly.
Serological tests are now considered to be more reliable and their accuracy has been validated by comparison to more costly and time-consuming analytical procedures. One such method is an ELISA test. Just a precaution, ELISA is prone to false positives in dirty environments.
Some elevators may be running an ELISA test for aflatoxin, so producers need to be sure to get good information on why the load was rejected. If you are told that aflatoxin was present at some level above the tolerance of 20 ppb (parts per billion) for grain and feed, there had to be something other than a fluorescence test run. If the level is close to 20 ppb, you might want to look into testing the load yourself in a laboratory.
Dr. Draper's recommendation is to be sure of what level of mycotoxin you have in that load of grain. Levels over 20 ppb are still usable on-farm, levels up to 100 ppb may be fed to breeding cattle, breeding swine, and poultry while levels up to 300 ppb may be fed to finishing cattle and swine.
Dr. Draper said it will be difficult to test for aflatoxin before harvest and have any certainty that you are getting reliable numbers for the actual level of contamination, but looking for ear molds may give you an idea of the risk. Aspergillus is a yellow-greenish colored mold. It may or may not be sporulating now.
If it is not sporulating, the yellowish color will not be obvious. The best thing to do is have your grain tested. Olsen Biochemistry Lab is prepared for in coming samples. All mycotoxin samples will be sent to NDSU for testing. If they are received by SDSU, they will be forwarded to Fargo. The charge for an aflatoxin test is $34 and the charge for a full mycotoxin screen (19 mycotoxins) is $90.
If your load is rejected, check with your crop insurance agent to see if it would be covered as an insurable loss. Also remember that an infected load cannot be co-mingled with grain from other fields.
For more information stop by the Extension office and pick up Bulletin 907: Aflatoxins Hazards in Grain/Aflatoxicosis and Livestock. Portions of this article come from this bulletin.