Mycotoxins

Mycotoxins are those secondary metabolites of fungi which are associated with certain disorders in animals and humans. The manifestations of toxicity in animals are as diverse as the fungal species which produce these compounds. In addition to being acutely toxic, some mycotoxins are now linked with the incidence of certain types of cancer and it is this aspect which has evoked global concern over feed and food safety. For ruminants, the mycotoxins of relevance are those arising from fungal contamination of protein supplements of tropical origin, principally cottonseed cake and groundnut meal, and certain grasses infected with endophytes. In addition, other grains and associated by-products may be contaminated with mycotoxins. When cottonseed cake and groundnut meal become infected with Aspergillus flavus and A. parasiticus, these meals are frequently contaminated with up to four aflatoxins, one of which (aflatoxin B1) is a carcinogen and may be converted into another potential carcinogen (aflatoxin M1) by lactating animals and secreted in milk. Aflatoxin contamination of cereals such as maize and sorghum may also occur and, in addition, worldwide contamination of maize with fumonisins has recently been reported. The fumonisins are synthesised by Fusarium moniliforme and have now been linked with the incidence of oesophageal cancer in humans and with outbreaks of animal mycotoxicoses in southern Africa. Well-defined syndromes have been identified in ruminants consuming forages naturally contaminated with toxigenic fungi. Of particular importance are the endophytic fungi of the Acremonium species which may infect tall fescue and perennial ryegrass, causing reduced productivity and neurological effects in cattle and sheep. The ergopeptine and lolitrem alkaloids have been implicated as the causative agents. In addition, infection of lupin stubbles, pods and seeds by Phomopsis leptostromiformis may result in the synthesis of the phomopsins which have been associated with lupinosis in sheep. Recent research indicates promising prospects for the development of plant genotypes devoid of, or resistant to, infection by toxigenic fungi. In the case of aflatoxin contaminated oil-seed meals, treatment with ammonia is a cost-effective method of detoxification.