Implications of mycotoxins in animal disease.

Mycotoxins are formed on animal feeds when conditions of moisture and temperature permit the growth of naturally occurring toxigenic fungi. In general, mycotoxins are low molecular weight, nonantigenic substances, many of which are relatively heat stable. Mycotoxins can cause acute disease episodes when animals consume critical quantities of them. Specific toxins affect specific organs or tissues such as the liver, kidney, oral and gastric mucosa, brain, or reproductive tract. In acute mycotoxicoses, the signs of disease often are marked and directly referable to the affected target organs. Most frequently, however, concentrations of mycotoxin in feeds are below those that cause acute disease. At lower concentrations, the effects of mycotoxins are more protean. They reduce the growth rate of young animals, and some interfere with native mechanisms of resistance and impair immunologic responsiveness, making the animals more susceptible to infection. These effects on immunity and resistance are difficult to recognize because the signs of disease are associated with the infection rather than with the mycotoxin that predisposed the animal to infection. Animals vary in their susceptibility to some mycotoxins, according to the species and age of animal; young growing animals are more susceptible to certain mycotoxins than are adults. The major effects, sources, and dose response relationships of mycotoxins important to the health of food-producing animals are presented in accompanying tables.