New research on hail-damaged corn led by Iowa State University (ISU) reveals that hail damage during grain fill adds to the risk of ear rot diseases and mycotoxin contamination.
The findings are important because hail-damaged corn is often fed to livestock, which can become ill or refuse feed if mycotoxin levels are too high.
“Hail damages crops somewhere in Iowa every year. But until recently, there was little data to quantify effects of hail damage on grain quality,” says ISU plant pathologist Alison Robertson.
Robertson analyzed damaged corn ears collected from several Iowa fields struck by hail storms in July and August 2009. The storms impacted 1.3 million acres of land in northeast and west central Iowa. Because the storms took place in later stages of the crop’s growth, it provided researchers a rare opportunity to study the effects of hail on grain quality.
Hail-bruised kernels reduce grain quality through growth of molds. Some molds produce toxins leading to ear rots; others discolor kernels, reducing marketability.
Researchers found as hail damage to kernels increased, so did the severity of ear rots and consequently the presence of certain mycotoxins.
Fusarium, gibberella and cladosporium were the main molds found. Fusarium ear rot can contaminate grain with toxins called fumonisins. Deoxynivalenol and zearalenone are toxins produced by the fungus that causes gibberella ear rot.
“Swine are very sensitive to vomitoxin,” Robertson says. “And zearalenone is an estrogen-type mycotoxin that can affect breeding pigs.”
These effects of zearalenone poisoning on reproduction are hard to spot, compared to vomitoxin, which produces more visible signs such as poor weight gain, adds ISU’s Steve Ensley with the Veterinary Diagnostic Laboratory.
The mycotoxins are contained in damaged corn and also distiller’s dried grains with solubles (DDGS), the byproduct of making ethanol. When damaged corn is used to make ethanol, any mycotoxins present concentrate up to three times in the DDGS, Robertson says.
Contaminated grain or DDGS can be blended with clean grain to get below advisory levels set by the Food and Drug Administration (FDA). For swine, the FDA advisory limit is 5 parts per million (ppm) for vomitoxin or no more than 1 ppm of total diet, and 1 ppm for zearalenone. Samples were not blended in this study, but researchers found about 10% of pure grain samples had mycotoxin levels above the FDA advisory limits for vomitoxin, zearalenone or both.
“This amount may seem small, but you need to factor in that approximately 65% of Iowa’s corn is used in the ethanol industry,” Robertson points out.
Taking that into account, Robertson estimates that “in actuality, more than 50% of the study’s grain samples had mycotoxin levels that would have concentrated in the DDGS to levels greater than FDA advisory levels.”
Even when blending grain, it can be challenging to evenly distribute clean and contaminated grain in the feed mix, says Ensley.
“It’s hard to get a homogenous mixture. There could be areas in the feed where concentrations of contaminated grain are higher,” he says. “Pigs are so sensitive to deoxynivalenol, this may cause them to go off feed and it may take two weeks to get them consuming feed normally again, even on totally clean grain.”
These findings illustrate the importance of regularly checking fields to monitor development of ear rot, and planning to harvest fields expeditiously if more than 10% of ears in a field are fairly moldy, Robertson suggests.
Pre-harvest scouting of fields can be an effective way to reduce the risks of mycotoxin contamination.
“Our research showed there was a positive correlation between visually damaged samples and detectable levels of toxins,” Robertson says. “So it’s very important to scout your fields to see how much ear rot you have.
“Our management recommendation is to harvest this damaged grain as early as possible, and dry and cool the grain immediately, to reduce growth of molds and minimize further development of these mycotoxins,” she concludes.