Evaluation of the potential growth and body composition of the Cobb MV x500 genotype.

The potential growth and body composition of modern broiler genotypes must be periodically re-evaluated to quantify the effects of continued genetic selection and to provide the information required for predictive growth models. This study characterized the growth potential of male and female Cobb MV × 500 broilers reared under non-limiting conditions from hatch to 105 d of age. Two hundred birds of each sex were fed ad libitum using a four-phase feeding program, and body weight, feather growth, physical body components, and chemical composition were measured serially throughout the growing period. Growth after feed withdrawal (empty BW) was described using the Gompertz function, and allometric relationships between body protein and the chemical and physical components of the body were determined. Males attained a higher mature BW and body protein weight than females, whereas females deposited proportionally more lipid. Mature empty BW were estimated to be 8.12 and 6.29 kg for males and females, respectively. Rates of maturing of the feather-free body were similar between sexes and comparable with those reported for contemporary broiler strains. Unusually, feather growth matured more slowly than the feather-free body. The hypothesis that, within a sex, all chemical and physical components of the body other than feathers could be described using a common rate of maturing was corroborated by the evidence presented. Water and lipid deposition differed markedly between sexes, whereas protein and ash contents remained relatively constant throughout growth. The resulting Gompertz and allometric coefficients provide a biologically consistent description of growth and body composition in this genotype and demonstrate that genetic improvement in modern broilers has been achieved primarily through increased mature size rather than major changes in developmental rate. These parameter estimates will assist in improving the prediction of nutrient requirements, feed intake, and changes in carcass composition in simulation models used for nutritional and management decision-making.