Maintaining albumen quality and reducing feed costs in laying hens through glycine and serine supplementation in low-protein diets

Reducing dietary crude protein (CP) in poultry nutrition is critical for sustainability, yet maintaining hen productivity remains a challenge. Supplementing low crude protein (LCP) diets with amino acids (AAs), particularly glycine (Gly) and serine (Ser), presents a promising strategy to enhance nutrient efficiency and maintain egg quality. This study investigated the impact of Gly and Ser supplementation on production, egg quality, blood biochemistry, ileum and magnum histology, gene expression, and AAs in blood and albumen with cost efficiency in laying hens. A total of 560 Hy-Line Brown hens (24 weeks-old) were allocated to eight treatment diets, including one LCP diet (14.50% CP) and a positive control (PC) diet (16.50% CP), with 10 birds per replicate. Six LCP diets were further supplemented with different Gly or Ser concentrations (0.067%, 0.134%, and 0.20%). Production performance, egg quality and egg AAs were analyzed. Blood samples were collected for serum biochemistry and AAs analysis. While ileum and magnum tissues were subjected to histology and relative gene expressions. Data were analyzed using one-way ANOVA (SAS) with Tukey's post hoc test. Results showed that LCP diets decreased egg weight (EW) and egg mass (EM) (P < 0.05), but supplementation with Gly 0.20% increased EW and EM than PC diet for weeks 1-12 (P < 0.05). Similarly, albumen height and AAs were improved in LCP + Gly 0.20% (P < 0.05). furthermore, LCP + Gly 0.20% enhanced ileal villus height/crypt depth ratio (P < 0.05), indicating improved nutrient absorption. Regarding genes expressions, both Gly 0.20% and Ser 0.20% addition resulted downregulated expressions and reduced PSPH levels (P < 0.05). Metabolically, Gly 0.20% or Ser 0.20% addition increased few non-essential AAs in portal and wing vein blood (P < 0.05), indicating a modulation of systemic amino acid availability. Economically, LCP diets reduced feed cost by 40 RMB/tons, while adding Gly 0.20% in LCP diet saved cost of 14 RMB/tons of feed. In conclusion, adding Gly 0.20% in LCP diet effectively restores egg production, improves egg quality, gut health, and metabolic status with reducing feed cost in laying hen diets.