This review presents a description of the growth of broiler and laying chicken strains studied at the Laboratory of Poultry Science, Universidade Estadual Paulista (UNESP)-Jaboticabal. Two commercial broiler strains and four laying strains were assessed.Ross 308~R and Cobb 500~R broilers were reared to 56 days of age using 1920 broiler chicks divided into four groups (two strains x two sexes), each with four replicates of 120 birds, resulting in 16 experimental units. The four laying strains studied, to 126 days of age, were Hy-Line Brown, Hisex Brown, Hy-Line White W-36 and Hisex White. Three hundred chicks of each strain, all females, were separated into groups to create four replicates of 75 birds, resulting in 16 experimental units. Every week, the birds were weighed and a sample was selected for carcass analysis based on the average weight of the experimental unit. Measurements were made of their chemical components (water, protein, lipid and ash) from which the growth of each component was described using the Gompertz function. Allometric coefficients were determined for the chemical components of the body in relation to the feather-free protein weight of the body. Differences between the broiler and laying strains were observed in some parameters of the Gompertz function. Among the broiler strains, differences were observed in the protein content of the body and in the weight of the feathers. Differences between laying strains were in protein weight and rate of maturing. The allometric coefficients revealed little difference between the genotypes, in both broiler and laying strains, indicating that it is possible to use generalized parameters to describe the growth of chemical components of the body using allometry. The different rates of growth between genotypes indicate that the intakes of energy and amino acids required to enable them to reach their genetic potential would differ between genotypes.
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