A survey of mycotoxigenic fungi and mycotoxins in poultry feed
The occurrence of fungi and their toxins in poultry feed lowers the hygienic quality of feed and presents several hazards to poultry and sometimes to 'man. To evaluate the magnitude of these hazards and generally the hygienic quality of feed presented to poultry in Nairobi, Kenya, several experiments were carried out. A total of 90 samples of poultry feeds were randomly sampled from farmers in peri-urban areas Nairobi province and in Kikuyu division of Kiambu district. dirty samples were collected in January, 30 in March, and 30 in May 1993. All the samples were subjected to moisture determination, mycological examination and mycotoxin analysis. Enumeration of total mould counts, Aspergillus spp. counts, Penicillium spp. counts, Fusarium spp. counts as well as identification of isolates of species belonging to these three genera was done. The aflatoxin producing ability of the Aspergillus flavus group isolates was tested on a synthetic medium. All feed samples were also analysed for aflatoxin B1, B2, G1, G2, ochratoxin A, zearalenone and sterigmatocystin. The total mould counts recorded were very high compared to the findings from other parts of the World such as Norway and Germany. They varied from 1 X 104 - 1.31 X 106 CFU/g. On the basis of these mould counts, the hygienic quality of 36%- of all the samples examined were classified as unacceptable. Aspergillus spp. , Penicillium spp. and Fusarium spp. were the most commonly isolated fungi sometimes accounting for all the fungi identified. Aspergillus spp. counts varied from 1.0 X 103 - 8 X 105. Penicillium spp. counts varied from 2.0 X 102 - 3.0 X 105 while Fusarium spp. counts varied from 0 - 3.1 X 105• A total of fifteen species of the genus Aspergillus, 19 of Penicillium and 3 of Fusarium were identified. Overall, Aspergill us flavus was the most commonly isolated species being demonstrated in 73.3% of all samples. When the aflatoxin producing ability of these A. flavus group isolates was tested on yeast extract sucrose agar, only 19.01% of all the isolates produced aflatoxins. Analysis of mycotoxins by thin layer chromatography revealed that 35.6% of all the samples were contaminated with at least one of the seven mycotoxins analysed for, with aflatoxins being the most abundant. They were found in 24.4% of the samples at levels of between trace and 50ppb. Ochratoxin A was detected in 10% of all samples, zearalenone in 5.6% and sterigmatocystin in 2.2% of all samples examined. Occurrence of several mycotoxins in one sample was recorded in 13.3% of all the samples. The moisture content varied from 6.79 % to 11.46 %. Statistical analysis showed no significant differences in the levels of total mould counts, moisture content, mycotoxin contamination and most fungal groups' counts in feed samples from different manufacturers or of different feed formulations. However, almost all these variables showed significant differences when feed sampled at different times was compared. Several conclusions are drawn from this study. (1) The level of fungal contamination of poultry feeds used in Nairobi is very high making most of the poultry feed unacceptable. (2) The majority of these contaminants belong to the genera Aspergillus, Penicillium and Fusarium and include many well known mycotoxigenic fungi species. (3) Aflatoxins are present in some of the feed used in Nairobi and surrounding areas, but at levels insufficient to cause clinical aflatoxicosis. (4) Mycotoxin other than aflatoxins, such as ochratoxin A, zearalenone and sterigmatocystin also occur in poultry feeds used in Kenya, sometimes as co-contaminants to the aflatoxins. (5) The frequency of contamination of poultry feed with mycotoxins vary with the month of the year. (6) Because of the low moisture content of feed recorded in this study, the mycotoxin contamination in mixed poultry feed is most likely as a result of use of contaminated raw materials and not due to fungal growth and toxin production in the mixed feed. For this reason, it is recommended that further studies be done to identify the most susceptible raw material and also have a continuous surveillance for mycotoxins in these raw materials.