**5. Deoxynivalenol content in wheat**

Deoxynivalenol, commonly referred to as vomitoxin, is a mycotoxin that may be produced in wheat and barley grain infected by Fusarium head blight or scab [39]. The fusarium head blight may infect grain heads when wet weather occurs during the flowering and grain filling stages of plant development. Although the occurrence of fusarium head blight is not necessary to mean that deoxynivalenol is present, a high level of scabby kernels in the harvested grain means deoxynivalenol will likely be present. Levels of deoxynivalenol do not necessarily correlate with levels of physical damage in grain. The impact of deoxynivalenol in feed grains on animal performance and health vary with type of livestock animals. The evident production losses were observed in non-ruminant animals, in particularly swine when vomitoxininfested grains were fed [40, 41]. Research conducted with vomitoxin-infested barley indicates no apparent problems when fed to growing and finishing cattle or gestating or lactating beef cows [42]. It appears that cattle can tolerate high levels of vomitoxin (21 mg deoxynivalenol/ kg wheat) without impacts on performance or health of the cattle [43]. However, exercise caution with wheat or any grain that has gone out of condition or has mold damage. The possibility exists that molds and toxins will impact feeding value through reduced feed acceptance, intake and performance, as well as higher incidence of morbidity, the possibility of abortion in pregnant cattle and, in some cases, even death. Young calves, gestating cows and animals under nutritional stress are most vulnerable [43].

The deoxynivalenol can be measured using several laboratory procedures. The most common method used by the Federal Grain Inspection Service and most grain handling and processing facilities is the immunological-antibody method called Enzyme Linked-Immunosorbent Assay (ELISA) because it is relatively fast and cheap. The gas chromatography-electron capture (GC-EC) analytical method is quantitative and used to calibrate ELISA test kits.

The inability to feed wheat with high levels of deoxynivalenol to be fed to swine and poultry contributes to the lower price of wheat, but the impacts of deoxynivalenol on the feed value of wheat for beef cattle are largely unknown. According to [5], the level of deoxynivalenol in North American wheat ranges from 0.3 to 1.0 mg/kg, however the level of deoxynivalenol measured in specific lots can reach levels of up to 20 mg/kg. The highest deoxynivalenol levels are also usually associated with soft rather than hard wheat [5]. The maximum tolerated deoxynivalenol level by Canadian Food Inspection Agent in diets for swine, young calves, and lactating dairy animals is 1 mg/kg, and 5 mg/kg in diets for cattle and poultry. Ruminants are considered quite resistant to Fusarium toxins such as deoxynivalenol because of the detoxifying potential of rumen microbes. Previous studies have shown that the epoxide group-bearing parent toxin deoxynivalenol is metabolized to de-epoxy-deoxynivalenol [44]. However, little is known about the effects of Fusarium toxins (i.e., deoxynivalenol, fumonisins, trichothecenes, zearalenone) or their metabolites on the activity of rumen microbes and the consequent effect on feed efficiency in ruminant animals.
