INFLUENCE OF PROTEIN-CONCENTRATION ON THE RESPONSE OF BROILERS TO SUPPLEMENTAL DL-METHIONINE

This experiment was conducted with male broiler chickens from 15 to 35 days of age to determine the effect of dietary protein content on the requirement for sulphur-amino acids. Six levels of DL-methionine were added to diets containing 20.5 or 24.2% crude protein. At each protein concentration there was a response in growth rate, feed efficiency, and carcass quality to methionine supplementation. Plateauing in growth rate or feed efficiency was not achieved with the highest methionine supplementation. Thus the requirement for maximum growth and optimum feed efficiency was more than 0.86% Met + Cvs with 20.5% CP or more than 0.95% Met + Cys with 24.2 CP. The sulphur amino acid requirement increased almost in direct proportion to the dietary protein level (with a ratio of about 0.025% additional Met + Cys per %-point additional protein). It is suggested to consider this relationship in diet formulation. Carcass quality was significantly improved by increasing protein and sulphur-amino acid concentrations. Slaughter yield and breast meat yield seemed to be more influenced by methionine level than by protein content, while fat content responded to both protein and methionine.