Drought harvests call for vigilance and a better understanding of toxins
Aflatoxin levels were variable this year, which can be expected during a widespread drought. Growing stress like we had this year increases the likelihood of moldy and mycotoxin-contaminated grain. It’s Aspergillus flavus that produces aflatoxin. Aspergillus likes it warm. It thrives at 80 to 85 degrees F. And during growing seasons like the one closing now, you might see other ear rot molds that tend to be problematic, including fusarium and penicillium molds.
Penicillium roquefortii is the most common. It likes it a bit cooler than Aspergillus—I saw it mostly during my tenure in Minnesota and Wisconsin. Fusarium can be particularly nasty. A common problem species is Fusarium moniliforme, which usually shows up as a whitish mold between the kernel and starburst on the kernels. It produces fumonisin, a known carcinogenic mycotoxin. This tends to be more common the further south you go in the US, and it is particularly tough on horses. Another fusarium trouble maker is Fusarium graminearum, which tends to be a pinkish mold.
We all know there are problems with molds producing mycotoxins, but not all molds produce mycotoxins. In fact, only a small number do. Some mold-free corn samples will test positive for mycotoxins, particularly if you are testing a high moisture sample. In most cases, the mycotoxins were formed while the crop was standing in the field. The longer the crop stands in the field, the longer the molds have time to grow before the conditions are altered to reduce their growth. Also, just because you see mold and fungi, it does not necessarily mean you have mycotoxins.
And some molds aren’t harmful at all. Smut, or Ustilago maydis, may infect corn ears, reducing yield and generally gumming things up, but research and field work indicates that cows will increase their intake of smutty silage over uninfected silage. Indeed, there are places where smut is eaten as human food. It is not an animal performance concern.
Tactics to lower the potential mycotoxin load:
1) Harvest the most heavily infected fields first.
2) Remove small, light broken kernels and pieces of cob and fines.
3) Use a grain cleaner prior to ensiling high-moisture corn or drying the corn.
4) Dry grain rapidly, this will NOT eliminate or degrade mycotoxins, but it will reduce the favorable conditions for continued mold growth.
5) Aerate the bins.
Further tactical considerations:
1) Often the cob is more heavily infected than the grain, so reducing cobs, particularly small pieces of cob, tends to reduce load.
2) The mold grows much better on cracked grain. It has a tough time getting through the kernel’s pericarp. Screening corn, and using only fully intact kernels will reduce load. It has been fairly well documented that aflatoxin will accumulate in the aleurone of the kernel.
3) Infected grain used for dry milling will have substantially higher levels of mycotoxins in the by-product (e.g. DDG) than the base grain.
4) Getting below 15 percent moisture makes the mold go dormant.
5) Fermenting feed will stop fungal growth, and mold counts will drop over time.
6) Appearance is useful within limitations—clumpy-wooly material is suspect. Black light tests for kojic acid, something that Aspergillus produces in growth.
Molds and mycotoxins clobber cows in a couple of different ways. Even if the mold does not produce a mycotoxin, it is still using nutrients that I would prefer that the livestock were getting. The mold may reduce animal acceptability of the feed. If the mold has produced mycotoxins, there is a long list of potential symptoms: poor performance, reduced intake, looking rough, etc. Mycotoxins may reduce feed consumption of animals by altering brain neurochemistry. These neurological conditions can induce lethargy and in some cases, it can make hogs vomit. Zearalonone is an estrogen that can lead to reproductive failures. Aflatoxin can cause immunosupression.
Getting the sample tested:
For dry grain samples, usually the lab will run an ELISA test. However for silages, ELISA tests tend to give false positives. For silages, a sample should be sent to the laboratory for analysis by thin-layer or gas chromatography. Gas chromatography is not so bad, but thin-layer chromatography is tedious.
If you have mycotoxin loads Feed Cattle Charge. While that might sound self-serving, we routinely test incoming ingredients, and we reject loads which exceed limits. From a practical perspective, consider diluting contaminated feed with mold-free feed. However, as pointed out earlier, toxin assays are necessary to determine correct dilution rates and the levels of toxins found are always changing.
If mycotoxin screens detect DON, zearalonone or T-2 contamination, dilute the feed to acceptable levels. Treating grain with anhydrous ammonia has been shown to reduce aflatoxin levels, but states vary in practices allowed. Roasting grain has also shown reductions in aflatoxin, but it is less effective than is ammoniation. Ozonation has worked in research settings, but it is not a practical method in the field. Applying mold inhibitors epropionic acid, will help minimize further mold growth, but will not destroy mycotoxins.
Contaminated feed can be fed to livestock classes less sensitive to the mycotoxin. Non-breeding mature cattle tend to be the most tolerant. Avoid feeding moldy feed to young, lactating or gestating animals. Sometimes the cheapest alternative might be to discard the feed rather than endure the loss of animal production.
You can also increase protein feeding. Animals on a protein-deficient diet are more sensitive to aflatoxin injury than those on a well-balanced ration. Likewise, increasing Vitamin A and E levels and feeding a chelated zinc source have been shown to mitigate effects of aflatoxin.
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Dr. Jim White is ruminant nutritionist for MFA Incorporated.