Laying hen responses to balanced protein reduction on performance, egg quality, nitrogen balance, and fat and mineral utilization

The effect of graded reductions in balanced crude protein (CP) on hen productive performance, egg quality, nitrogen balance, abdominal fat deposition, tibia traits, and relative economic outcomes from 26 to 44 wk of age (WOA) was investigated. A total of 252 26-wk-old Hy-Line Brown hens were housed in enriched cages (seven birds/cage) and randomly allocated to one of four different dietary CP levels of iso-energetic diets with nine replicates per treatment. The trial was conducted over two phases of 26 to 34 and 36 to 44 WOA. Diets included a high-protein (HP; 18.0% and 17.0% CP in Phases 1 and 2), medium-protein (MP), low-protein (LP), and very low-protein (VLP) series, representing stepwise reductions of 0.50, 1.00, and 1.50 percentage points relative to HP. Limiting amino acids (AA; lysine, methionine, and threonine) were supplemented to ensure balanced AA profiles. Collected data were analyzed using the general linear model (GLM) procedure for one-way ANOVA; statistical significance was set at P < 0.05, and trends were noted at 0.05 < P < 0.10. Balanced protein reduction tended to improve abdominal fat contents (2.66% to 2.85%; P = 0.059), but reduce body weight gain (141.66 to 95.66 g; P = 0.089), particularly with the VLP diet. Across 26 to 44 WOA, graded CP reduction lowered egg weight (60.36 to 59.40 g; P < 0.05) and feed conversion efficiency (1.93 to 1.97 g feed/g egg; P < 0.05); and tended to reduce egg mass (57.02 to 55.11 g/hen/day; P = 0.080), particularly in the VLP group. As to egg quality, Haugh units were higher (P < 0.05) with HP and MP diets (94.60 and 94.30) than LP and VLP diets (93.66 and 93.04) across 26-44 WOA. In contrast, LP and VLP diets tended to improve yolk color (8.38 to 8.49; P = 0.076) and egg-breaking strength (5.39 to 5.51 kg; P = 0.058) across 26-44 WOA. Dietary CP reduction linearly reduced nitrogen consumed and excreted by more than 10% (P < 0.05). Tibia-breaking strength tended to decline with dietary CP reduction (P = 0.094), decreasing from 27.62 kg in HP to 25.54-25.68 kg in the LP and VLP diets. Economically, reduced CP lowered egg income (P < 0.05) at weeks 34 and 44 (2.00 to 1.77$; 1.96 to 1.89$, respectively); and feed costs at week 34 only (0.54 to 0.52$; P = 0.088), but profit margins remained unaffected (P > 0.10). Conclusively, these results confirm the effectiveness of balanced dietary protein reduction in maintaining egg production rate and most egg quality traits while reducing nitrogen excreted and feed costs.