A comparison of growth and development patterns in diverse genotypes of broilers. 1. Male broiler growth.

Selection for breast muscle yield and BW in commercial broilers has resulted in genotypes far different from broilers processed in the past. When comparative studies with commercial lines are conducted, it is often difficult to differentiate between carcass effects resulting from direct genetic selection vs. correlated effects that partially reflect genetic changes in BW. The objective of the present experiment was to compare growth and development characteristics of male broilers from commercial lines exhibiting similar rates of BW gain based on a percentage of 8-wk BW but exhibiting different carcass traits. Male broilers from 2 commercial genotypes exhibiting increased breast muscle yield (A and B) were compared with broilers from a commercial line that was "unimproved" with respect to conformation (C). All birds were fed a commercial-type broiler starter diet throughout the study and were processed at 8 wk of age for carcass comparisons. No differences were observed among lines for breast-free BW or weight of the abdominal fat pad. The absolute and relative weights of pectoralis major and pectoralis minor breast muscles were heavier in lines A and B than C (P < 0.001). Length (C > A > B; P < 0.001), width (B > C >A; P < 0.001), and depth (A = B > C; P < 0.001) of the pectoralis major were different between lines. Drum and thigh weights were heavier in lines A and B than C (P < 0.001). There were genotype differences in tibia length (C > A = B, P < 0.001) and femur length (C > A = B, P < 0.001). The comparison of line C with selected lines A and B, suggested that line C may provide a useful model for studying carcass development between commercial genotypes with similar growth patterns.