1. Three experiments using sixty individually fed, enzootic pneumonia-free Large White pigs on experiment from 9–11 weeks of age to 200 lb live weight are described.
2. Information was obtained on the effect of different dietary concentrations of aflatoxin B1 on the performance of the pigs, on various biochemical measurements and on the histology of the livers and kidneys.
3. Reduced growth rate and loss of appetite were the main adverse effects observed, their extent being positively related to the dietary level of aflatoxin B1. No marked clinical signs were seen, mortality was very low and there was little or no effect on the feed conversion efficiency of the animals.
4. No evidence for any adverse interaction between aflatoxin B1 and the presence in the diet of a supplement of copper sulphate providing 250 ppm Cu was apparent from either the performance, biochemical or histological results obtained. It was concluded that the few isolated reports of toxicity in growing pigs fed diets containing a supplement of 250 ppm Cu were unlikely to have been the result of the unsuspected presence of aflatoxin B1 in the feedingstuffs used in the diets.
5. Aflatoxin B1 tended to increase the serum alkaline phosphatase level, the concentration of Cu in the kidneys, and liver weight and to reduce the liver vitamin A concentration. No other consistent differences in the measurements made were observed.
6. The extent of the total pathological abnormality observed in the livers and kidneys was closely related to the level of aflatoxin B1 in the diet.