Toxigenic fungi and the deterioration of Nigerian poultry feeds
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Growth of toxigenic strains of Aspergillus clavatus Des. and Aspergillus flavus Link at 30°C on milled poultry feeds led to a considerable decrease in the protein, oil and crude fibre contents of the feed substrate. A corresponding increase in the free fatty acid fractions of the feeds due to the activities of these microbes was also recorded. Rapid degradation of the feedstuff by both species was recorded at a temperature of 25°C and 30°C and a pH range of 4.8–6.4. When grown on feed infusion broth at 30°C, the highest amounts of mycelial production with sporulation of both fungal species occurred within the 8-day incubation period. A determination of their extra-cellular enzyme profile showed the production of amylases, pectate lyase, cellulases, proteases, lipases, xyalanases, DNase and RNase.
All the carbon and nitrogen sources used (except L-sorbose and DL-tryptophan), supported good mycelial growth with sporulation. An optimal C∶N ratio of 5.0∶4.5 and 7.5∶3.0 was recorded for growth and sporulation of A. clavatus. For A. flavus, a C∶N ratio of 7.5∶4.5 was found best for growth and 5.0∶3.0 for sporulation.
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