Abstract

Samples silages, mainly maize, from dairy farms in KwaZulu Natal, South Africa were obtained and analysed for fungi and mycotoxins with a view to ascertaining if there were any dangerous levels of these contaminants present. The silage was also examined for dry matter, pH, yeasts and bacteria and these were found to vary from area to area but did not show any striking differences from other studies. Fungi were detected by a serial dilution technique using restriction agar. Several species of the mycotoxin-producing genera, namelyAspergillus, Fusarium and Penicillium were found. The most predominant of these was Aspergillus fumigatus,a known human pathogen, whereas Fusarium spp. were not present to any degree indicating their suppression by the ensiling process, as maize in the field is susceptible to these fungi. Mycotoxins were detected by thin layer chromatography, Vicam immuno-affinity clean-up system and high performance liquid chromatography. Four (total aflatoxins, deoxynivalenol, ochratoxin A and zearalenone) mycotoxins were found in varying quantities in the silage, while fumonisins were only found in chopped maize samples. Cytotoxicity testing was performed on human blood monocytes using mycotoxin positive and negative extracts. The results showed that cytotoxicity testing could be applied to silage extracts as a preliminary screen to detect mycotoxins. Consequently, the results indicate that maize silage can be a source of mycotoxins in the food chain, which is of particular importance where dairy cattle consume aflatoxins, due to possible contamination of milk with aflatoxin M₁.

Key words: Fungi, maize, mycotoxin, silage.