Microflora of more than 100 samples of different sorts of foodstuff (coarse fodder, grain forage, mixed fodder, premixes, silo, whole milk substitute etc.) selected in 1989-1992 in the period of mass diseases and death of animals in farms of Ukraine has been studied. It is shown that the amount of spore material included in lg of fodder, depends on the sort of feed substrate. Grains and grain forage (94.5 thou. spores in 1 g) occupy the first place in sporification with fungi; vetch-oat mixture and whole milk substitute (82-89 thou. spores)--the second place; mixed fodder granules and maize briquettes (79.5-66.5 thou. spores)--the third place; the latter are mixed fodder plants hay, cereals straw (11.8-43.5 thou. spores). Aspergillus mainly occurred on the concentrated forage, grain, grain forage, in less amount--in grass stand, cereals straw. Penicilli, fusari and other species of saprophytic fungi dominated on hay of natural meadows, on mixed fodder plants and cereals straw. It has been stated that the highest toxicity was typical of the fodder samples infected with Aspergillus strains producing kojic acid. Under conditions of our experiments out of 67 strains of genus Aspergillus kojic acid was synthesized by 48.6% of the total number of the tested fungus cultures. The greatest number of kojic acid producers was found among Aspergillus flavus isolates (56.8%) the less number--among A. fumigatus (36.7%). Kojic acid has been revealed to exert a pathological effect on the organism of different animal species.