Growth patterns and conformation in broilers: influence of genotype and management on isometry of growth

Log-linear regression equations of log-transformed weekly broiler growth data and allometric growth equations (in actual measure) were fitted with body weight as the predictor variable and shank length, keel length, breast width, and thigh width as response variables. Data were obtained on two commercial broiler genotypes (G1 and G2) reared on litter floor and in wire cages. Growth of each of the structural body components relative to growth of the body as a whole during a 12-wk growth period was similar in both cage and floor-reared groups. Analysis of the 12-wk pooled data from both cage and floor groups indicated the occurrence of isometric growth of the shank and breast in G1 and of the breast only in G2 and allometric growth of the thigh and keel in both genotypes. When starter and finisher growth phases were considered separately, data showed growth patterns generally similar to those of the different body parameters in the 12-wk period. This suggests that characterization of individuals on the basis of relative growth response for selection purposes can be done equally accurately during any phase of growth.