The drought of 2012 has the potential to increase mycotoxin risks, particularly aflatoxin concentration in this year’s corn crop. Conditions favorable for aflatoxin production include drought stress during corn silking stage and nighttime temperatures greater than 70 degrees F. An informational Web site is found at http://vetmed.iastate.edu/diagnostic-lab/diagnostic-services/diagnostic-sections/chemistry-/-toxicology/aflatoxin-iowa
To detect mycotoxins in grain, especially aflatoxin, visual examination is not effective. The black light test can be used only as a marker of potential aflatoxin content (as it identifies Kojic Acid). Quick enzyme-linked immunosorbent assay (ELISA)-based test kits for first level screenings have been developed but need to be used in a controlled environment by a qualified technician. Matrix interference is important with ELISA testing, and confirmation by a chemical assay is recommended. Accurate interpretation of results is essential.
Aflatoxin will damage the liver and result in poor performance. The pig pictured below on the left is consuming a normal diet, while the one on the right is consuming feed with aflatoxin.
Safe levels of aflatoxin are less than those that are known to compromise productivity. The graph below is a general guide of levels that can cause measurable effects on animal productivity.
Aflatoxin can affect both humoral and cell-mediated immunity and will reduce resistance to several infectious diseases. Young animals are generally more at risk for the effects of aflatoxins. The concentration in feed and duration of exposure both contribute to the severity of effects, with liver a target organ in swine (Figure 1).
Figure 1.Periportal Fibrosis, Bile Duct Hyperplasia and Fatty Degeneration in a Liver Damaged by Aflatoxin
Aflatoxins are very potent, with measurements of actionable levels in parts per billion or ppb (Table 1).
Guidelines for Sampling
Mycotoxins are not evenly distributed in feeds or grain bins so accurate detection depends upon the quality and quantity of sample provided for analysis. The sample should reflect all of the feed available at the time the problem occurred. Feedstuffs collected after onset of animal health problems are more likely to not be characteristic of the feed being eaten at the time the problem began. The smaller or fewer the samples and subsamples collected, the more likely mycotoxin contamination will be missed.
The presence or absence of visible mold growth is not a reliable indicator of the presence or absence of mycotoxins. Very moldy feed may not contain any detectable amounts of known mycotoxins, while “good-looking” feed may contain very high concentrations.
It is best to collect a sample during movement of the feed, such as when feed is being augered from the storage bin into a grain truck. Collect small amounts (subsamples) over the entire time the feed is being moved, so that at least 5 lb., and as much as 10 lb., have been collected for submission to an analytical laboratory. Probe samples can also be used, collecting probe samples from as many areas of the feed as is practical.
Dry samples are preferred for transport to the laboratory. Mold may grow on wet samples, especially if the sample is placed in a plastic bag. Oven-dry samples to less than 13% moisture for best preservation. Ship samples in paper or cloth bags.
The Veterinary Diagnostic Laboratory at Iowa State University provides quantitative analysis of feed for multiple mycotoxins (including aflatoxin). An informational Web site is http://vetmed.iastate.edu/diagnostic-lab/diagnostic-services/diagnostic-sections/chemistry-/-toxicology/mycotoxins. Several commercial feed laboratories also provide some level of aflatoxin screening.
Table 2 lists other potential mycotoxins found in grains.
The Food and Drug Administration guidelines have established “action levels” for acceptable concentrations of aflatoxins in specified foods and feeds: http://www.ngfa.org/files/misc/Guidance_for_Toxins.pdf.
For more information: