Cottonseed meal in broiler diets. 2. Considerations of some aspects of amino acid balance and gossypol level in cottonseed meal and cottonseed-meat meal starter diets

Three broiler starter experiments investigated the inclusion of cottonseed meal in diets based on grain sorghum. In the first, 35.5 per cent cottonseed meal inclusion in lieu of 28.5 per cent soyabean meal was studied. Additional 0.05 per cent ferrous sulphate, to counteract gossypol toxicity in the cottonseed diets, increased feed consumption by 4.3 per cent and improved liveweight gain by 2.2 per cent. Dietary leucine at 1.25 per cent tended to give better performance than either 1 .I 5 or 1.35 per cent. No differences in performance occurred with isoleucine levels of 0.54 - 0.74 per cent. On the better cottonseed diets growth rate equalled that on the soya controls, though feed conversion was inferior. In the second experiment meat meal protein replaced 0, 25 or 50 per cent of the cottonseed meal protein. Growth was optimal on the cottonseed meal diet with 1.35 - 1.45 per cent total dietary lysine. On the meat meal-cottonseed meal diets, lysine levels of between 1.10 - 1.45 gave no significant differences in growth rate or feed efficiency. Leucine supplementation in addition to lysine did not affect performance. Overall, the diets with one-half meat meal protein substitution for cottonseed meal protein resulted in significantly depressed growth. In the third experiment, half the cottonseed protein was replaced by either a 'normal' meat meal or a meat meal containing blood. The cottonseed meal-normal meat meal diet was shown to be equally deficient in leucine and isoleucine, whereas the cottonseed meal-meat meal with blood diet was deficient in isoleucine only. With adequate amino acid supplementation, the performance on these cottonseed meal-meat meal diets was not inferior to that of a control diet based on soyabean meal.