Extended periods of wet weather during the recent corn harvest accelerated the development of mold-infected corn, and with it, concerns about the presence of mycotoxins.
John Patience, swine nutritionist with Iowa State University, has assembled an extensive fact sheet — “Mycotoxin Contamination of Corn” — in which he describes the troublesome mold, what it does to pigs and what can be done about it.
Mycotoxins in corn are produced when certain molds infect the ears.
“Molds may only produce mycotoxins under certain environmental conditions, so testing for molds is not an accurate way to determine mycotoxins' presence,” Patience says. There are thousands of types of molds capable of growing on corn, but only a few species produce mycotoxins.
Most Prevalent Molds
The four major mycotoxins of concern to pork producers are aflatoxin, deoxynivalenol (DON or vomitoxin), fumonisin and zearlenone, all produced by ear rot in corn. T-2 toxin, produced by the same mold as DON, is less common than DON, but is more potent, he adds.
Molds are caused by organisms called fungi that cling to soil, decaying organic matter and plants such as corn. Hundreds of thousands of molds exist, but only a few compromise livestock and human health, he says.
Following is an abbreviated description of mycotoxins and some practical management recommendations from the fact sheet developed by Patience.
Molds on corn deteriorate feeding quality and may produce mycotoxins, which affect pig performance and health. Mold-free corn can also become infected in the grain bin. Mold growth requires moisture, so drying corn is a key step in breaking the cycle of mold growth in stored corn.
A variety of molds affect the ears of corn and cause a number of diseases, including Diplodia Ear Rot, Gibberella Ear Rot, Fusarium Ear Rot and Alfatoxin Ear Rot.
To minimize the presence and extent of mold infection:
- Control insects that can damage corn kernels. Insect damage to kernels allows fungi to establish themselves.
Adjust the combine to reduce kernel damage. Broken corn offers easy access to fungi, allowing them to grow more easily than in intact kernels.
Manage corn moisture levels. For example, uninfected corn at 18% moisture can only be safely stored for just over a month at 70°F, while corn at 13% moisture can be stored for 26 months at the same temperature.
If corn drying capacity is overwhelmed due to the wet harvest, a number of options are available. The first is to dry the corn to 17-18% moisture and then aerate to bring the moisture down to 14% needed for summer storage. The second option is to dry it in two passes: first to 17-18%, and later to 14%. The third and least desirable option is to dry corn to 17-18% and either sell or use the corn before the warm weather arrives. However, if corn is infected with mold, drying must occur sooner and the ultimate target is 13%.
Realize that low-test-weight corn will not store as well as regular corn; storage times are reduced up to 50%. Use or sell this corn first before it deteriorates further.
Don't store wet corn overnight in a wagon or truck, if at all possible.
Use aeration if drying is not possible; recommended rates for wet corn are 0.2 cfm/bu. Properly managed, aerated grain should stay at 28 to 35°F throughout the winter.
Rapid on-site test kits can provide early detection. When toxins are found, harvest affected fields first and follow the drying and storage recommendations outlined above. Don't delay harvest and grain drying to limit mycotoxin production, Patience suggests.
Harvest infected fields and store separately the corn from fields showing significant amounts of ear rot.
Remove fines from corn, as broken kernels are 3-4 times more susceptible to mold growth than intact kernels.
Be sure storage structures are thoroughly cleaned before filling with grain. Repair bin damage to stop moisture.
Clean corn can be stored at 16-17% moisture in winter, but moldy corn should be dried to 15% to prevent further growth. Dry down to no more than 13% moisture in the spring.
Providing good aeration in stored corn helps prevent moisture buildup in bins. Be vigilant about monitoring bin temperatures to prevent mold growth.
Some mold inhibitors have been used successfully to impair mold growth.
Next Page: Mycotoxin Detection
Two options are available for sampling corn at the time of harvest. Sampling is critical, because a truckload or field of corn may contain hot spots of mycotoxins, while the bulk of the field or truckload is clean. Improper sampling can result in missing contaminated corn, leading to false positive tests. Use a grain probe to sample corn from throughout the whole truckload or collect multiple samples while the truck is being unloaded.
Thoroughly mix the load samples and retain a 10-lb. sample. Pull a 1-2-lb. subsample for a rapid detection test or for submission to a diagnostic laboratory.
Use of Infected Corn
“One of the greatest frustrations about mycotoxins is what to do once you learn you have contaminated corn,” says Patience. A few options include:
Sell contaminated corn and buy back clean corn.
Analyze corn for common mycotoxins and dilute with clean corn to reduce contamination to safe levels for feeding to pigs.
Clean corn to remove fines and broken kernels. This will help reduce the concentration of mycotoxins overall.
If it must be fed, feed contaminated grain to market hogs only; avoid feeding mycotoxins to the breeding herd, if at all possible. Cattle are much less susceptible to the effects of mycotoxins than pigs.
Patience says the complete fact sheet will be available by the end of January on the Iowa Pork Industry Center Web site: www.ipic.iastate.edu.