The dynamics of body composition in yellow-feathered broilers

The objectives of this study were to: 1) fit the growth curve of body weight, components, and composition according to the Gompertz model; 2) predict body energy from body protein and fat based on multiple linear regression; and 3) identify the best predictors of body protein or fat based on an allometric growth model. A total of 840 1-d-old Qingyuan Partridge chickens were assigned to two gender groups (initial body weight: male 27.31 ± 0.12 g, female 27.54 ± 0.49 g), with six replicates of 70 chicks each. The birds were weighed every 10 d over a 120-d period. The body components (breast or thigh muscle and abdominal fat) were measured by dissection, and body composition (water, protein, fat, and ash content) was measured by whole carcass homogenization. The Gompertz model was used to fit the growth curve, and the derivative function was further applied to assess the daily growth rate. Multiple linear regression was used to calculate the body protein and fat energy content. Allometric functions were fitted to compare the growth rate of body components and composition to body weight. In male broiler, the Gompertz equation for body protein mass was $W_t=464.30\times e^{{-e}^{-0.027\times \left(t-55.67\right)}}$ ; and the equation for body fat mass was $W_t=192.50\times e^{{-e}^{-0.042\times \left(t-46.24\right)}}$ . In female broiler, the equation for body protein mass was $W_t=328.56\times e^{{-e}^{-0.027\times \left(t-52.01\right)}}$ ; and the equation for body fat mass was $W_t=437.81\times e^{{-e}^{-0.024\times \left(t-71.93\right)}}$ . The growth of male breast muscle and female thigh muscle were the most proportional to body protein deposition, as exponent was close to 1. In conclusion, the Gompertz model efficiently depicted body weight, components, and composition change. The Gompertz equation for body protein and fat can be applied to further model daily nutrient and energy requirements.