LIVE PERFORMANCE AND CARCASS YIELD OF MALE BROILERS FROM 2 COMMERCIAL STRAIN CROSSES RECEIVING RATIONS CONTAINING LYSINE BELOW AND ABOVE THE ESTABLISHED REQUIREMENT BETWEEN 6 AND 8 WEEKS OF AGE

A total of 1,440 male broilers from two commercial strain crosses, Peterson x Arbor Acres (PAA) and Ross x Ross (RR), was grown to 6 wk of age on crumbled starter (23.2% CP with 1.21% lysine and 3,231 kcal AME(n)/kg) and grower (20% CP with 1.01% lysine and 3,234 kcal AME(n)/kg) rations. One-half of the 24 birds from each pen were processed and deboned at 6 wk of age. The remaining birds subsequently received experimental rations from 6 to 8 wk of age based on corn, soybean meal, and corn gluten meal (basal ration = 18.1% CP and 2,961 kcal AME(n)/kg) containing increasing levels of dietary lysine (.75, .85, .95, 1.05, and 1.15% of complete feeds). All birds were then processed and deboned as performed at 6 wk. The main effects of dietary lysine and strain were analyzed by analysis of variance as a factorial arrangement at 8 wk of age. Live performance of PAA at 8 wk was significantly better than RR, and neither strain cross responded to lysine. The RR had a significantly lower percentage of abdominal fat, and greater percentages chilled carcass and yields of breast "fillets" (Pectoralis major), and "tenders" (Pectoralis minor) than PAA at both 6 and 8 wk. Dietary lysine alone did not affect any carcass characteristic, however, interactions existed between strain and lysine for abdominal fat, breast fillets yield, and tenders yield, which indicated that RR was at advantage for all factors when lysine attained .85%.