Effect of lysine and methionine supplementation of low protein roaster diets fed after six weeks of age.

Three floor rearing experiments were conducted using male broilers to determine the extent to which the protein level of the diet can be reduced by supplementation with the amino acids methionine and lysine. Corn-soybean type diets were used and three protein levels (18, 15, and 12%) were tested. All rations were computer formulated and those containing 15 and 12% protein were supplemented with DL-methionine and L-lysine HCl. Three replicate pens of about 50 males per pen were assigned to each treatment. Experimental diets were fed from 6 to 10 weeks of age in Experiment 1 and 6 to 9 weeks in Experiments 2 and 3. Birds were all group weighed at weekly intervals and feed consumption determined. Results obtained in Experiments 1 and 3 showed that neither body weight nor feed efficiency was reduced by feeding either 15 or 12% protein diets as long as these diets contained the National Research Council (NRC, 1977) recommended level of methionine and lysine. In Experiment 2 the 12% protein level depressed body weight and feed efficiency. Net returns over feed cost were highest with the 15% protein level in all three experiments. These results indicate that the NRC (1977) recommendation of 18% protein for 6- to 9-week-old broilers may be reduced with adequate amino acid supplementation.