With predictions of another week of wet weather in the upper Midwest, harvest of corn and soybeans will lag even further behind the 5 year average. In conversations with producers, I’m hearing reports of stalk rot and other stand problems.
Along with stand issues, conditions are ripe across much of the corn belt for an increase in corn quality problems associated with mold growth. This week I learned of one producer who has combined corn from 2 different locations and both sites tested above 4 ppm DON (deoxynivalenol or vomitoxin) and zearalenone. His agronomist has since visited many of his fields, and all have noticeable mold growth on the ear tips, suggesting a good share of the harvest will have quality issues.
In reviewing a NebGuide on grain molds from the University of Nebraska written by Dr Jim Stack, extension plant pathologist, mold growth can be expected to increase in years of stress, such as high moisture in mid-to-late season after a dry summer. After only 10.4 inches of rain from April 1 to September 25 in the Mankato area, the 5+ inches since then fit this description of circumstances very well.
For those that sell corn, many country elevators use long wave length ultraviolet light (blacklight) as a screen for the presence of mold growth. This is not a reliable test for corn destined for human or pig consumption as many molds and mold toxins do not fluoresce under black light. In addition, many compounds unrelated to mold or mold growth will fluoresce. On the other hand, grossly molded grain may contain no detectable toxins that impact pig performance.
Fungi capable of producing mycotoxins include Aspergillus, Fusarium, Penicillium and others. Toxins produced by the Fusarmium species include DON and Zearalenone, contaminants in the producer’s grain mentioned earlier. Infected corn kernels may be pink or show a white starburst pattern radiating from the top of the kernel.
DON is concern at levels of 1 ppm or higher in swine diets as pigs refuse to eat feeds with grain at this level of contamination. In general, at levels of DON contamination above 1 ppm, pigs will immediately try to sort feeds in an attempt to locate particles not contaminated. With complete diets now routinely ground to a particle size of 700 microns, sorting is not an option for the pig, so a reduction in feed intake occurs. As levels of DON increase, there may be total feed refusal. I had this experience more than 10 years ago in my research unit at the University of Nebraska, and it is humbling to see feeders full of what appear to be very good quality feed, and pigs refusing to eat.
There are very few binders that can be added to swine diets when DON contamination occurs. The general recommendation is to blend the contaminated corn with non-contaminated corn until the combined corn DON level is below 1 ppm. This suggests if you’ve got old crop corn, use it sparingly in pig diets until you have some experience with new crop corn – you may need it to blend down toxin levels.
Zearalenone mimics reproductive hormones. In grow-finish gilts, there is often vulval swelling, while in breeding herds a variety of reproductive failures can occur. In general, toxin binders are more likely to be effective in zearalenone contaminated feed stuffs.
Many state veterinary diagnostic laboratories can furnish information on testing for toxins and guidance on levels of concern in swine diets. Having been a faculty member at the University of Nebraska for so many years, I continue to rely on the information from there. An excellent series of NebGuides on mold and mycotoxins can be found at: