Vomitoxin

Vomitoxin, also known as deoxynivalenol (DON), is a type B trichothecene, an epoxy-sesquiterpeneoid. This mycotoxin occurs predominantly in grains such as wheat, barley, oats, rye, and maize, and less often in rice, sorghum, and triticale. The occurrence of deoxynivalenol is associated primarily with Fusarium graminearum (Gibberella zeae) and F. culmorum, both of which are important plant pathogens which cause Fusarium head blight in wheat and Gibberella ear rot in maize. A direct relationship between the incidence of Fusarium head blight and contamination of wheat with deoxynivalenol has been established. The incidence of Fusarium head blight is strongly associated with moisture at the time of flowering (anthesis), and the timing of rainfall, rather than the amount, is the most critical factor.

F. graminearum grows optimally at a temperature of 25 °C and at a water activity above 0.88. F. culmorum grows optimally at 21 °C and at a water activity above 0.87. The geographical distribution of the two species appears to be related to temperature, F. graminearum being the commoner species and occurring in warmer climates. Deoxynivalenol has been implicated in incidents of mycotoxicoses in both humans and farm animals.

Vomitoxin is rather a mild toxin compared to other toxins which can form in grains and forages. Reduced feed intake, and the accompanying decrease in performance, are the only symptoms of vomitoxin toxicity livestock producers will likely encounter. This response to vomitoxin appears to occur through the central nervous system. Vomitoxin belongs to a class of mycotoxins (tricothecenes) which are strong protein inhibitors. Inhibition of protein synthesis following exposure to vomitoxin causes the brain to increase its uptake of the amino acid tryptophan and, in turn, its synthesis of serotonin. Increased levels of serotonin are believed to be responsible for the anorexic effects of DON and other tricothecenes. Irritation of the gastrointestinal tract may also play a role in reducing feed intake... This fact may also partially explain the high incidence of pars esaughageal stomach ulcers observed in sows off feed during feed refusal.


 * Human foods: Vomitoxin is not a known carcinogen as with aflatoxin. Large amounts of grain with vomitoxin would have to be consumed to pose a health risk to humans. The FDA has established a level of 1 ppm (parts per million) restriction of vomitoxin.
 * Companion animals: Dogs and cats are restricted to 5 ppm and of grains and grain byproducts and that the grains not exceed 40% percent of the diet.
 * Livestock and farm animals: In animals and livestock, vomitoxin causes a refusal to feed and lack of weight gain when fed above advised levels. Restrictions are set at 10 ppm for poultry and ruminating beef and feedlot cattle older than 4 months. Ingredients may not exceed 50% of the animal's diet. Dairy cow limits are set at 2 ppm.