The replacement of some of the soybean meal by the first limiting amino acids in practical broiler diets. 2. Special additions of methionine and lysine as partial substitutes for protein in finisher diets.

1. Four trials were conducted to determine to what extent dietary protein concentration could be lowered while maintaining the concentrations of methionine and lysine, the first two limiting amino acids. 2. When the protein concentrations of well-balanced standard finisher diets were lowered by replacing soybean meal with sorghum grain (milo), there were progressive decreases in growth rate and increases in food consumption in spite of the substitution raising the energy content of the diets. 3. Maintaining methionine and lysine concentrations partly or completely reversed these trends. 4. Adding 0-12% methionine (above that generally considered to be the normal level in finisher diets) plus 0-20% lysine replace about 3 to 4 percentage units of soybean protein. 5. The recommended level of lysine supplementation may be exaggerated, since preliminary data indicate satisfactory results with a special supplementation of 0-10% each of methionine and lysine.