A study was conducted to determine the effects of crude protein (CP) reduction with amino acid (AA) balanced diets on growth, carcass yields, litter characteristics, and ecological footprint of feeds in mixed-sex broilers. A total of 2,688 Cobb MV × 500 FF broilers were allotted to 4 treatments (14 replicates of 48 birds per pen) from 11 to 36 d of age reared in an open-sided barn. Dietary treatments included: 1) Control diet (C) with DL-Met+L-Lys+L-Thr, 2) C+L-Val 3) C+L-Val+L-Ile and 4) C+LVal+L-Ile+L-Arg. Treatments in mash form were offered in the grower (11 to 25 d) and finisher (26 to 36 d) phases. Crude protein in the grower phase (SID Lys = 1.12%; AMEn = 3,100 kcal/kg) were 21.7, 20.5, 19.4 and 18.2% while in the finisher (SID Lys = 1.02%, AMEn = 3,180 kcal/ kg) were 19.6, 19.3, 17.9 and 17.4%, respectively. Nitrogen (N) utilization was calculated using feed intake, CP of diets, final BW and assuming 30 g N/kg BW. Composite litter samples were collected from 4 replicate pens per treatment at 25 and 35 d of age and analyzed for pH, water, N-NH3 , and K+ contents. The ecological footprint of feeds was calculated using GABI database. Data were analyzed using one-way ANOVA and means were separated by Tukey´s HSD with statistical significance considered at P ≤ 0.05. Overall (11 to 36 d) reduction of CP did not affect (P > 0.05) BW gain, feed intake or mortality. Feed conversion was similar across treatments up to C+L-Val+L-Ile, but C+L-Val+L-Ile+L-Arg had increased (P ≤ 0.05) FCR compared to the control. Final BW and carcass parameters as percentage of BW were not affected (P > 0.05). Overall N-utilization was improved (66 vs. 59%) and N excretion reduced (28 vs. 39 g/bird) in C+L+Val+Ile+L-Arg compared to the control. Reduction of dietary CP reduced litter´s moisture (P = 0.02), K+ (P = 0.02) and tended to reduce N-NH3 (P = 0.06). Relative to control, the climate change with land use (kg CO2 eq.) footprint of C+L+Val+Ile+L-Arg was reduced by 18 and 12% in the grower and finisher phase, while the eutrophication (kg P eq.) potential was reduced by 15 and 10%. Reduction of CP with an appropriate use of supplemental AA maintained growth and carcass yield parameters while improving litter quality, N-utilization and the sustainability of broiler production.
Key Words: amino acids, broiler, crude protein, nitrogen, sustainability