Comparative growth and development of Nicholas and hybrid toms from 16 to 82 days and effects of protein restriction from 0 to 59 days on growth of hybrid toms through 125 days of age.

The objective of this experiment was to study age and diet effects on serial growth of economically important carcass parts of Nicholas (NIC) and Hybrid (HYB) toms. At approximately 14-d intervals from 16 to 82 d, BW and the weight of selected carcass parts were compared in toms from both commercial strains. There were no overall strain differences in BW, although NIC toms were heavier from 31 to 72 d, which resulted in a significant strain by age interaction (P < or = 0.021). The absolute weight of the Pectoralis major (PMAJ; P < or = 0.022) and tibia plus associated muscles (Drum; P < or = 0.051) were increased in NIC toms. The relative weight of the PMAJ (P < or = 0.004) and abdominal fat (72 and 82 d; P < or = 0.023) also were heavier in NIC toms. The relative weight of the drum and Gastrocnemius muscle (GAS-TROC) was heavier in HYB toms, however (P < or = 0.001). A separate set of HYB poults was fed a diet deficient in protein or lysine (PD) from 0 to 8 wk and their growth and carcass development were compared with those fed a Control diet (NRC, 1984). Comparisons also were made at approximately 14-d intervals from 16 to 125 d. The PD diet from 0 to 8 wk significantly reduced BW and absolute breast muscle and leg portion weights. The relative weight of the PMAJ and Pectoralis minor (PMIN) were also reduced in toms fed the PD diets but the thigh and drum (125 d) were increased.