MYCOTOXINS are fungal toxins, but not all fungi produce mycotoxins, Dr. Erin Bowers recently told attendees at the 2014 Grain Elevator & Processing Society's Exchange in Omaha, Neb.
Mycotoxins are found worldwide and affect cereal crops, but there are also mycotoxins that affect nuts, coffee, beans, fruits and a variety of other crops.
Bowers, a post-doctoral research associate with Iowa State University's agriculture and biosystems engineering department, said for North American grains, there are five primary mycotoxins of concern: aflatoxin, deoxynivalenol (vomitoxin), fumonisin, zearalenone and ochratoxin.
"Corn can be affected by all five of the mycotoxins, whereas it is much less common for aflatoxin to be found in something like wheat," Bowers explained.
Deoxynivalenol, zearalenone and ochratoxins are more prevalent in wheat, while barley is typically only affected by deoxynivalenol and ochratoxins. Hot and dry conditions provide a good environment for the development of aflatoxins, fumonisins and ochratoxins, while cool and wet conditions favor the development of deoxynivalenol and zearalenone.
"We're concerned with mycotoxins because they cause a number of detrimental health effects to humans and in animals," Bowers said.
Aflatoxins in livestock lead to increased mortality, reduced weight gain in production animals, reduced egg production in poultry and reduced milk production in dairy cattle.
Fumonisins have been associated with feed refusal and pulmonary edema in swine and equine leukoencephalomalacia (ELEM), which is essentially the fatal liquefying of brain matter in horses, mules and donkeys.
Deoxynivalenol makes pigs vomit, but symptoms also include nausea, diarrhea and feed refusal, and it can cause reduced milk production in dairy cattle. Zearalenone has reproductive effects in ruminants, while ochratoxins increase mortality, decrease weight gain and reduce egg production in poultry.
A number of things can be done, from in the field to when the grain is stored, Bowers said. For example, irrigation is helpful for managing the mycotoxins that thrive in hot, dry conditions.
"Making decisions that promote plant health is the best way to fend off some of these mycotoxin-producing fungi. If you have a healthy plant, it is much easier for that plant to defend itself against colonization," she said.
According to Bowers, a lot of the fungi colonize on crop debris, so the spores easily get stirred up with wind or water. "When you turn that over through tillage, it helps disperse that inoculum, and it also keeps it away from easy transport routes," she said.
She pointed out that crop rotation is another good option to prevent mycotoxin growth, especially if using host and non-host plants in the rotation. For example, corn is a host plant, but soybeans aren't, so rotating the two is a great management option.
Insect management is also a primary concern because insects can carry the spores on their bodies into or onto the plant. Bowers said one example of insect management is using Bt corn to help reduce fumonisins.
In areas with aflatoxin contamination, Bowers said certain hybrid selections can help. "Fungi like to grow down the silks, so tight-husked hybrids have been pretty effective in reducing the amount of spores that are able to infect the tip of the ear and then colonize the rest of the ear," she said.
One of the trickiest parts about mycotoxins, according to Bowers, is that they are not distributed evenly in grains; they typically occur in contamination hotspots. This, she said, can occur when a contaminated area of a field is harvested and then is dispersed unevenly in storage. It can also occur in storage if there are isolated areas of heating or increased water activity.
Bowers said 20 parts per billion of aflatoxin is equivalent to as few as six contaminated corn kernels in 10,000, which is also approximately six kernels in 6.25 lb. of 15% moisture corn.
"You can see that it takes very little kernel colonization to actually cause a problem," Bowers told attendees. "This 20 ppb is the lowest action level for aflatoxin. If you don't detect those accurately, it can cause real problems for categorizing that grain and effectively putting it in the right market."
Bowers noted that the U.N. Food & Agriculture Organization has created a mycotoxin sampling tool that can be found at www.fstools.org/mycotoxins.
In terms of sampling, she recommended increasing the sampling size and said it is the cheapest way to increase the accuracy of detecting contamination within lots. Using a sample size of 0.25 lb. hugely increases the risk of misidentifying lots of grain, according to Bowers.
"You can't test every load, but be aware, and know what your risk is based upon the crop, the weather conditions and your location," Bowers recommended.