Reduction of dietary protein in broiler diets not only reduces n-emissions but is also accompanied by several further benefits

In the light of recently revised German legislation on on-farm nitrogen (N) management, the impact of decreasing dietary N-load at balanced dietary amino acid supply on growth performance and N-excretions was examined in 5000 mixed-sex Ross 308 broilers from 1 to 40 d of age (20 floor pens with 250 birds each). In addition to diets representing the German standard with 22.0, 20.6, 20.0, and 19.5% crude protein (CP) in starter (1–10 d), grower I (11–16 d), grower II (17–30 d), and finisher feed (31–40 d), a N-reduced German standard (21.0%, 20.0%, 19.6%, and 18.9% CP) was fed in treatment 2. Dietary CP was further reduced in treatment 3 (21.0%, 19.5%, 18.7%, and 18.0% CP) and treatment 4 (21.0%, 19.0%, 18.0%, and 17.0% CP). Growth performance, feed conversion (FCR), carcass quality, N-utilization and litter quantity (at termination) were examined. Final body weight were similar between treatments 1, 2, and 3 but slightly impaired in treatment 4 (P < 0.05) while FCR was not affected. Carcass and breast meat yield did not differ significantly between treatments in male broilers. In female broilers, carcass yield was similar between treatments 1, 2, and 3 whereas it was lower in treatment 4 (P < 0.05). Breast meat yield of female broilers did not differ between treatments (P > 0.05). Dietary N-reduction resulted in gradually improved N-utilization (P < 0.05) resulting in reduction of N-excretion (P < 0.05). Moreover, quantity of litter at termination of the trial gradually decreased with dietary protein while dry matter content of litter increased and N-content decreased (P < 0.05).