The dynamics of body composition and body energy content in broilers.

Body composition (BC) analysis is important because the modern broiler is one of the most efficient animals in producing protein for human consumption, and a proper nutrition could potentiate this meat production. BC by chemical analysis was analyzed in 151 broilers from 1to 60 d of age. Birds were fed mash feeds ad libitum in four phases (starter 1 to 14d, grower 15 to 28 d, finisher 29 to 42 d, and withdrawal 43 to 60 d). Gompertz 3P model, multiple linear regression, and CRD with ANOVA analysis were used in the experimental design using JMP pro 2015. The growth in terms of body weight, protein, fat, minerals (Ca and P) followed a Gompertz 3P model with similar growth rates of about 4.9% per day and the maximum growth was obtained at about 34 d of age. Body weight ranged from 56 to 4184 g, water from 683 to 751 g/kg, protein from 154 to 182 g/kg, fat from 53 to 101 g/kg, minerals (ash) from 17.9 to 22.5 g/kg (AS IS basis). Broiler protein ranged from 563 to 613 g/kg, fat 197 to 317 g/kg, minerals 65.2 to 86.6 g/kg, calcium 11.7 to 18.9 g/kg, and phosphorus 10.3 to 15.3 g/kg dry matter (DM) basis. The calorific coefficients for protein and fat were determined by multiple regressions and resulted in 5.45 ± 0.09 kcal/g for protein and 8.95 ± 0.16 kcal/g for fat. These two coefficients can be used to predict the body energy content or energy of gain. The protein: fat ratio was the highest at day 1 and decreased gradually until day 60. The BC in terms of water, protein, and fat changes with age, water being reduced and protein and fat increased towards d60. Mineral composition remained constant at the end of growth but some fluctuations occurred during the grower period. The understanding of the dynamics of BC will bring new opportunities to study and change feed strategies and increase the feed efficiency for meat in the modern broiler.