There are consistent reports of worldwide contamination of feeds with fungi and their spores. In the tropics, Aspergillus is the predominant genus in dairy and other feeds (Dhand, Joshi and Jand, 1998). Other species include Penicillium, Fusarium and Alternaria, which are also important contaminants of cereal grains (D'Mello, Macdonald and Cochrane, 1993). Fungal contamination is undesirable because of the potential for mycotoxin production (see next section). However, spores from mouldy hay, silage, brewers' grain and sugar-beet pulp may be inhaled or consumed by animals with deleterious effects termed "mycosis". Common examples of such conditions include ringworm and mycotic abortion. The latter may occur in cattle as a result of systemic transmission and subsequent proliferation in placental and foetal tissues.