1. The effects of including small quantities of groundnut meal heavily contaminated with aflatoxin in the diets of calves and fattening cattle were studied.
2. Inclusion of 4% or 8% of the toxic meal in concentrate diets for early weaned calves significantly depressed live-weight gain and food intake prior to 3 months. The depression in live-weight gain was due to lowered food intake and to impaired food utilisation.
3. Inclusion of 4% to 12% toxic meal in meal mixtures consumed at 12–13 lb. daily for 20 weeks had no effect on the performance of fattening cattle.
4. Enlarged hepatic cell nuclei were found at slaughter in livers from calves which had received toxic meal and the incidence of these slight lesions varied with toxic meal intake. A very small incidence of similar lesions occurred in fat cattle fed on the highest level of toxic meal.
5. Complete exclusion of groundnut meals containing appreciable amounts of aflatoxin from the diets of calves and dairy cows, and its very limited use in diets for store and fattening cattle is recommended.