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Expert: Test wheat grain and straw for vomitoxin before feeding to livestock

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Written Thursday, July 08, 2010  

In a year when overly wet conditions and a head scab outbreak are significantly impacting Ohio's wheat crop, there is no room for assumptions that grain or straw is toxin-free and safe to feed to livestock.

To avoid any health problems in cattle, swine, poultry and other animals, growers are highly encouraged to test the grain for vomitoxin levels before any of the feed or grain by-product is destined for consumption.

"Farmers shouldn't think that it's okay to handle or feed scabby grain without actually testing and knowing how much toxin is in it," said Pierce Paul, an Ohio State University Extension small grains specialist and plant pathologist. "I always emphasize testing."

Wheat in some portions of Ohio is experiencing upwards of 60 percent incidence of head scab—a disease that attacks the wheat during flowering under wet, humid conditions. The disease can impact yields. The fungal pathogen that causes head scab also produces mycotoxins (most notably vomitoxin) in the grain that can be unsafe for livestock if consumed in high levels.

"Much of Ohio's wheat crop is testing positive for vomitoxin, with results ranging from 1 part per million to as high as 10 parts per million," said Stan Smith, OSU Extension program assistant. "In some cases, the grain elevator is accepting the wheat after discounting the price anywhere from a nickel per bushel up to more than a dollar per bushel. In some cases, the wheat has been rejected at any price by the elevator."

The situation, while not ideal for wheat growers, may be an opportunity for livestock producers, who value wheat for its higher protein content compared to corn. However, livestock producers must recognize the sensitivities of each livestock species to vomitoxin before incorporating any wheat grain into feed rations.

For grain and grain byproducts destined for consumption by ruminating beef, dairy, or feedlot cattle older than four months, and chickens, the limit is 10 parts per million. For beef cattle, the total diet should not exceed 10 ppm, but for dairy cattle, the diet should not exceed 5 ppm. For chickens, ingredients with 10 parts per million should not exceed 50 percent of the diet. For grain fed to swine, and all other animals, the limit is 5 parts per million, with the limit not exceeding 20 percent of the diet for swine and 40 percent of the diet for all other animals.

Bill Shulaw, OSU Extension beef and sheep veterinarian, said that swine are most susceptible to vomitoxin-infected grain, while beef cattle have the highest tolerance.

However, vomitoxin isn’t the only mycotoxin produced by the Fusarium pathogen that farmers have to worry about. "Hence, the importance of testing the grain suspected of being contaminated," Shulaw said. "Although swine are the most susceptible to the effects of vomitoxin (vomiting and feed refusal) and cattle are more resistant, some of the other mycotoxins produced by Fusarium species, such as T-2 toxin or fumonisin, can cause clinical and subclinical diseases. If farmers plan to feed wheat or other feeds they suspect has mycotoxin contamination, testing a representative sample would be wise." However, obtaining a representative sample is not an easy thing to do.

Producers have also inquired about safely using potentially contaminated wheat straw as bedding for livestock species and horses. The fear exists that animals will ingest the straw.

OSU Extension specialists indicate that as long as ample feed is available, animals are unlikely to ingest large amounts of wheat straw. In addition, horses, like cattle, have a high tolerance for vomitoxin-infected grain.

"However, the vomitoxin concentration in straw is something that dairy farmers specifically need to take note," said Maurice Eastridge, OSU Extension dairy specialist. "Many dairy farmers feed small amounts of straw to lactating dairy cows as a source of fiber, often at 10 percent to 20 percent of the diet. For example, a diet containing about 2 pounds of straw containing 10 parts per million of vomitoxin would result in about 2 parts per million of vomitoxin in the diet. However, the straw may be higher in concentration of vomitoxin than 10 parts per million, and other feeds in the diet may contain vomitoxin or other mycotoxins. Also, higher levels of straw are often fed to dry cows compared to lactating cows."

If samples are going to be sent to a lab, it is important to submit samples for the appropriate tests of vomitoxin, Eastridge said. "ELISA tests designed for grains most often don't work well for forages, so make sure the appropriate test is used."

A list of laboratories that will analyze for mycotoxins is available at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mycotoxin%20text2.htm .

The occurrence of head scab in wheat does not automatically mean vomitoxin, but high levels of scabby kernels in harvested grain are suspect and should be tested.

For more information on mycotoxins, log on to http://beef.osu.edu/library/mycotoxins.html . Information on head scab and vomitoxin can be found at http://agcrops.osu.edu and http://beef.osu.edu/beef/beefJune3010.html .


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