Nigeria has one of the fastest growing population in Africa. Increasing population and nutritional knowledge may put pressure of demand on the dairy industry, which may in turn compromise the quality of dairy products. The likelihood of heavy contaminations of dairy cattle feeds and milk products by fungi and aflatoxins, in this part of the world, may be encouraged by the prevailing climatic conditions. Such level of contamination could be of greater concern, with over 80% of dairy production in Nigeria, in the hands of pastoralists, who have little or no knowledge of the subject matter. Majority of Nigerians, mostly in the low and rarely of the medium economic status, depend largely on locally produced and processed milk and milk products for protein supplementation. It therefore, implies that, many consumers are exposed to the risks of aflatoxin and other health related issues through consumption of contaminated dairy products. The aim of this study therefore was to investigate the occurrence of aflatoxigenic strains of A. flavus and their aflatoxins B1 and M1 (AFB1 and AFM1) in dairy cattle feeds and milk products from Fulani herd groups and conventional dairy herds in Kaduna State of Nigeria. The major objectives of the study were to isolate and identify the toxigenic strains of A. flavus from feeds using phenotypic means and identify the strains by PCR methods. Their metabolic products were also detected and quantified from feeds, milk and milk products using Enzyme linked Immunosorbent Assay (ELISA) and and High Performance Liquid Chromatography (HPLC) techniques for screening and confirmation. Out of the total of 144 dairy feed samples collected and analyzed in this study, 86 (59.7%) had fungal contamination of which 48 (55.8%) and 16 (18.6.7%) were A. flavus and A. parasiticus respectively. Of these proportions, 12 (18.8%) and 4 (6.3%), were identified as aflatoxigenic strains of A. flavus and A. parasiticus respectively. The average fungal colony forming units (CFU) determined in this study was 4.5 Log10 CFU/gram of feed. This level is below the EU recommendation of 5.0 Log10 CFU/g for poorly preserved feeds. Feeds fortified with concentrates, feeds of cereal grains only and hay were evaluated for levels of contamination by both aflatoxigenic and non-aflatoxigenic strains of A. flavus.
In any of the feed type, there were relatively higher proportions of non-toxigenic strains (66.3 – 79.1%) than the aflatoxigenic strains (20.9 – 33.7%). Out of 144 dairy feed samples collected for testing using comparative analytical methods, 86.8% and 91.6% samples tested positive for aflatoxins B1. Of the positive samples, 92.0% showed AFB1 contamination levels at ≥ 5 ppb of which 56 (49.0%) had AFB1 contamination levels of up to and above 20ppb. Significant proportions of these AFB1 positive samples were feeds fortified with concentrates (14.6%), feeds of grain origin (8.3%), stored feeds (16.7%) and feeds from small holder‘s farms (>43.8%). A total of 201 milk and milk products were tested for AFM1 in this study, of which 174 (86.8%) and 197 (98.0%) of all the products tested positive for AFM1 with HPLC and ELISA analytical methods respectively. In this study, factors such as size and type of dairy farms seemed to have influence on the level of aflatoxin contamination. For instance, small scale dairy farms, comprising mostly of Fulani herds, showed significant proportion (91.7%) of samples positive for AFM1 contamination. Other factors of influence studied amongst others included, effects of heat-treatment temperatures on AFM1 concentration, such as milk sterilization at 121oC which showed reasonably lower AFM1 concentration of 142.09 ppb than the lower temperature treatment of 80oC which showed an AFM1 concentration of 183.58 ppb, when compared with the original fresh unpasteurized milk (219.98 ppb). Locally fermented yoghurt (Kindirmo) and milk (Nono) displayed relatively lower mean AFM1 concentrations of 0.158±0.025ppb and 0.231±0.019 ppb. Findings from this study have indicated potential health risks associated with the consumption of dairy products, particularly those products processed locally. Therefore, adequate and all-inclusive measures are recommended to be put in place for routine monitoring of dairy products including the locally processed products before they are marketed for human consumption in Nigeria.