Effect of low-protein diets and single sex on production performance, plasma metabolites, digestibility, and nitrogen excretion in 1- to 48-day-old broilers.

Two experiments were conducted to investigate the effect of low-CP diets supplemented with crystalline amino acids, according to an ideal amino acid ratio, on the performance, plasma metabolites, nutrient digestibility, nitrogen balance, and water intake in male and female chickens from 1 to 48 d of age using a 4-phase feeding program: prestarter (1-7 d), starter (8-21 d), grower (22-35 d), and finisher (36-48 d). Three experimental diets were formulated for each phase: a control diet with a CP level of 24.5, 23.0, 21.5, and 20.5%, respectively, and medium- and low-CP diets containing 1.5 and 3% less than that of the control, respectively, but the same ME and digestible lysine levels. In experiment 1, in males, the reduction in dietary protein content by 3% increased the feed conversion ratio (P < 0.05) in the starter, grower, and finisher phases, and plasma albumin levels were reduced (P < 0.05) during the prestarter, starter, and finisher phases. In females, the same effect on plasma album levels was observed (P < 0.05) only in the starter phase. Sex affected plasma albumin levels during the prestarter, starter, and finisher phases, being higher in females. In experiment 2, the reduction in dietary protein content linearly decreased water consumption in both sexes (P < 0.05). The reduction of dietary protein by 1.5 or 3% reduced nitrogen excretion to the environment by 9.5 and 17% in males and by 11.8 and 14.6% in females, respectively. In summary, the low-CP 4-phase feeding reduced water intake and nitrogen excretion with an adverse effect on the feed conversion ratio in males but not in females. So, single-sex rearing could be used to reduce the environmental impact of chicken farms.