The effect of feeding high levels of low-quality proteins to growing chickens.
1. Three growth trials were done using male broiler chicks. In the first two trials, groundnut meal was used, with and without supplementary methionine and lysine. In the third trial, soya-bean meal was used with and without supplementary methionine. Protein levels ranged in the first trial from 120 to 420 g/kg diet and in the third trial from 120 to 300 g/kg diet. Thus the assumed minimal amino acid requirements of the chick were supplied by high levels of low-quality dietary protein. 2. Diets based on cereals and groundnut meal did not support maximum live-weight gain or maximum efficiency of food utilization at any level of dietary protein. When the principal deficiencies of lysine and methionine were corrected, this protein mixture was capable of supporting the same growth rate as a control diet of cereals and herring meal. 3. Diets based on maize and soya-bean meal did not support quite the same growth rate as similar diets supplemented with methionine, even though the protein level in the unsupplemented diets was sufficient to meet the assumed methionine requirements. 4. These results are interpreted as examples of amino acid imbalance in diets composed of familiar feeding-stuffs. It is concluded that one cannot assume that the poor quality of a protein source can always be offset by increasing the concentration of dietary protein.