The replacement of some of the soybean meal by the first limiting amino acids in practical broiler diets

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Abstract
1. Three trials were carried out in order to determine the amount by which dietary protein concentration can be reduced while maintaining the dietary concentrations of the first two limiting amino acids, methionine and lysine. 2. In all trials growth rate and food utilisation declined as the protein concentration of a well‐balanced standard chick diet was lowered by replacing soybean meal with sorghum grain (milo), but this trend could be partly or completely prevented when methionine or methionine and lysine levels were restored. 3. Addition of 0.06 to 0.07% methionine, above that considered to be normal, is sufficient to replace approximately 0.9% soybean protein. 4. In diets containing approximately 3 percentage units less soybean protein than required, a supplementation of about 0.15% each of methionine and lysine can replace nearly 2.0% soybean protein, but cannot bring about chick performance equal to that obtained on the control ration, indicating an insufficiency of a third, or third and fourth, limiting amino acid in such low‐protein diets.