**Acknowledgements**

*Aflatoxin B1 Occurrence, Detection and Toxicological Effects*

toxigenic strains were isolated.

conditions prevail during the rainy season.

for aflatoxin production. Nonetheless, detection of aflatoxins in a sample means the substrate has been contaminated by toxigenic species which could either be present or absent at the time of sampling. This was the case with the feed concentrates which had aflatoxin concentrations higher than the grass samples, but fewer

The most dominant aflatoxin across all feeds was AFB1 with an average concentration of 9.0 μg/kg and was detected in all the samples that tested positive for aflatoxin contamination. This is above the EU 5 μg/kg set for lactating cows. Udom et al. [39] and Gizachew et al. [25] also reported their samples having AFB1 concentrations exceeding the EU regulatory limit. The high levels of AFB1 in most samples could be attributed to the fact that it was the most common and prevalent aflatoxin in most food matrices [40, 41]. Moreover, some authors have indicated that most toxigenic *Aspergillus* strains produce AFB1 and therefore it occurs more frequently than the other aflatoxins [10, 42, 43]. AFB1 was predominant in the rainy season (**Figure 8**). These results are in agreement with the findings by Chohan et al. [36] which also showed high concentrations of AFB1 during the rainy season. For aflatoxin production, high temperatures and high humidity are required, and these

However, for brewers' spent grains (BSG), AFB2 was the predominant aflatoxin. The BSG are a product of beer brewing industry [44] and has been found to be of valuable use in the feedstock industry mainly because it is affordable and available throughout the year [45]. BSG used in this study were from the production of opaque beer. The presence of aflatoxins in beer production has been associated with contaminated malt. Malt production involves increasing the moisture content of the grains to allow partial germination of the grain. Aflatoxigenic fungi are known to contaminate cereal grains which are also used in the beer production process [46]. If the malt is not properly dried or stored, fungal growth may be promoted resulting in the production of aflatoxins. Research on the fate of mycotoxins during the beer fermentation process showed that recovery of AFB2 in BSG is higher than other aflatoxins [47]. Some researchers [48] showed that AFB2 is able to adsorb onto yeast cells during fermentation. The yeast cells and the grain particles that are removed through filtration are collectively known as brewers' spent grains. This could be the possible reason why AFB2 levels were higher in BSG samples. Nevertheless, Gonzalez Pereyra et al. [38] were not able to detect any AFB2 in barley malt and brewers' spent grains from Argentina breweries. AFB1 has been reported as the most common aflatoxin occurring naturally in feedstuffs, but for this study it was not the case for BSG as the concentration of AFB2 was higher than that of AFB1. This study also showed that aflatoxin contamination of brewers' spent grains, a known source of nitrogen and roughage, and grass were within the regulatory limits making them safer when compared to the concentrates and mixed ration. However, nutritional composition of the grass will not meet the dietary demands of the cows.

Detection of aflatoxins in the feed samples used for this study is a cause of concern as this may be indicating the possibility of transfer into the milk by the dairy cows. Although most samples were within the acceptable limit for total aflatoxin, it was noted that concentrations of AFB1, the most potent of them, were above the regulatory limit. Moreover, research has shown that AFB1 can be carried over into milk as its hydroxylated metabolite AFM1 making milk a route through which humans are exposed to aflatoxins. High prevalence of AFB1 during the rainy season could be an indication of poor storage of the feeds which may result in increased

**46**

**5. Conclusion**

I would like to thank the farmers who participated in this research; without you I would not have done it. I am also grateful to the farm personnel who assisted in the collection and safe storage of the samples, thank you for your immense support.

I also want to thank the NRF (Grant number 105882)and the NUST Research Board (Grant number RB No. 43/16) for the funds that were made available towards this research.
