Lysine need of heavy broiler males applying the ideal protein concept.

An experiment was conducted to measure the response of broiler males to dietary lysine progressing from 0.75 to 1.15% between 42 and 56 d of age. Chicks (Ross x Ross 308) were placed in floor pens (30 pens having 35 chicks each) of an open-sided house and provided common feeds to 42 d of age. From 42 to 56 d, a corn-soybean meal diet (18% CP and 3,250 kcal/kg ME) having total lysine at 0.75% was supplemented with additions of 0.10% until 1.15%. All other essential amino adds were "ideally" balanced to one another within the limits of practicality assuming 0.85% total lysine. Birds had continuous access to feed, water, and light. Live performance during experimentation was particularly favorable. Weight gain between 42 and 56 d of age was similar among birds receiving all levels of lysine, while feed conversion was optimized at 0.85%. Depot fat removed from the abdominal cavity, yield of the resultant chilled carcass, and the amount of fillet (pectoralis major) cone deboned from the breast were unaltered by dietary lysine level. However, yield of tenders (pectoralis minor) decreased as supplemental lysine increased, whereas the incidence of myopathy (green muscle disease) increased. The lysine requirement of 0.85% as advocated by NRC (1994) for broilers between 42 and 56 d of age is in agreement with present results and may have been predisposed by its favorability of balance with all other essential amino adds.