Reducing dietary crude protein in broiler diets does not compromise performance and reduces environmental impacts, independently from the amino acid density of the diet

SUMMARY: The objective of the present experiment was to investigate the influence of dietary crude protein (CP), standardized ileal digestible (SID) Lys level and their interaction in male Ross 308 broilers. From day 10, six experimental treatments were tested until day 35. The 6 experimental treatments consisted in a 3 × 2 factorial design with 3 levels of dietary SID Lys/CP (equivalent to 3 levels of dietary CP) and 2 levels of dietary SID Lys. Growth performance, uniformity, carcass traits, litter quality, blood & gut parameters, nitrogen (N) emissions, and global warming potential (GWP) were measured or calculated. There was no interaction for all criteria except for NH3 and N2O volatilization. The increase of dietary SID Lys/CP did not affect growth performance or uniformity, increased abdominal fat yield, decreased all N related parameters (litter N, blood uric acid, N excretion, NH3, and N2O volatilization). There was an interaction between dietary CP and AA origin for GWP; GWP was further reduced after CP reduction when using AA from EU. Increasing SID Lys improved growth performance, increased uniformity, increased breast meat yield, reduced abdominal fat yield, but increased N emissions and GWP. This study indicates that dietary CP can be drastically reduced in different nutritional contexts without negatively affecting growth performance, and with positive benefits on the environment.