Performance, nutrient digestibility, and muscular evaluation of female broiler chickens fed different dietary protein levels and slaughtered at 38 or 46 days

This study evaluated the effects of two protein levels and types of formulation on performance, nutrient metabolization, and myopathies of 390 female broilers from 21 to 46 days old distributed in a completely randomized design, with five treatments and six replicates of 13 broilers each. Treatments were two levels of protein (19.0 and 21.0%) in diets using only commercially available ingredients and three experimental formulations designed to keep similar the main nutrients that could influence nutritional performance (starch, fiber, ether extract), using unusual ingredients, with 19.0% (19E) or 21.0% (21E) crude protein and the third with 19.0% crude protein with amino acid levels similar to treatment 21P (19E+Aa). We studied broiler performance, nutrient digestibility, macroscopic muscular evaluation, and histological muscular evaluation. The design for the performance and myopathy assessment was a 5 x 2 factorial scheme, five diets x two ages (38 or 46 days). The worst feed conversion ratio was observed for the 19P treatment. Neither diet nor age had an effect on myopathies, however, older slaughter age increased the intensity of microscopic lesions. The diet 19P should be avoided and increased inclusion of lipids in diets improves nutrient utilization and, consequently, performance.