Background: Tryptophan (Trp) is a limiting amino acid in poultry nutrition. Dietary supplementation of Trp not only enhances production performance, but also supports intestinal barrier integrity, alleviates stress, and boosts immunity, in which the derivatives from gut Trp-metabolizing commensal microbes play crucial roles. However, research on how excessive Trp affects poultry growth, metabolism, and gut microbiota composition remains limited. Methods: In this study, we investigated the effects of varying Trp levels (0.23%, 0.29%, 0.35%) on broiler production performance, immune function, and antioxidant levels through controlled feeding trials. These host responses were further correlated with cecal microbiota metagenomic sequencing data using multivariate analysis. Results: Compared with the basal 0.23% Trp level, a 0.35% of Trp addition significantly impaired broiler body weight gain and feed intake, and 0.29% Trp could increase thymus index and serum superoxide dismutase (SOD) level without affecting the growth performance; neither of these two levels affected the feed conversion rate. The cecal microbial metagenomic data further revealed that Trp supplementation reduced the abundance of harmful bacteria, while increasing the abundance of beneficial bacteria and Trp-metabolizing microorganisms. Correlation analysis showed that Trp supplementation was negatively correlated with body weight (BW) but positively correlated with thymus index and SOD level, with similar trends observed between the abundance of specific Trp-utilizing microorganisms and these indicators. Functional analysis revealed an increase in the abundance of KEGG orthology (KO) related to Trp metabolism from the aforementioned microbes. Conclusions: An appropriate addition of Trp (0.29%) can enhance certain metabolic levels without affecting production performance, which might be achieved through relevant metabolic pathways of intestinal microorganisms.

The suboptimal efficacy of a low-protein diet in small white-feather broilers is due to a lack of alignment with their specific nutritional requirements. To investigate these precise requirements and to promote the application of low-protein diets in these birds’ feeding, we evaluated the effects of graded crude protein (CP) levels under fixed amino acid supplementation in small white-feather broilers. A two-phase feeding trial (1–21 and 22–42 days) was conducted using 480 chicks that were 1 day old, and the experimental diets contained varying CP levels (Phase 1: 18, 19, 20, 21%; Phase 2: 16, 17, 18, 19%) while maintaining constant levels of limiting amino acids. Key findings revealed that Group 3 (Phase 1: 20% CP; Phase 2: 18% CP) exhibited superior early growth performance during days 1–21, with fecal nitrogen excretion reduced by 11% relative to that in Group 4. Additionally, carcass characteristics, serum biochemical parameters, and serum antioxidant capacity were compared across all groups. These findings offer initial insights into the effects of low-protein diets on small white-feather broilers and lay the groundwork for future amino acid optimization studies.

To determine dietary metabolizable energy (ME) and crude protein (CP) levels of Hy-Line Brown male chicks and compare response surface methodology (RSM) with artificial neural network (ANN) modeling, a total of 2160 birds were assigned to a 4 × 3 factorial design with three growth stages. Both RSM and ANN were fitted to predict body weight gain (BWG) and feed-to-gain ratio (F/G), with performance evaluated via LOOCV, leave-2-treatments-out validation, and bootstrap resampling. The 22–56-day stage yielded the best model performance overall. For F/G, both models achieved strong and comparable fit (in-sample R² ≈ 0.86–0.88; LOOCV retention ≈ 97%), and both remained predictive under leave-2-treatments-out validation (RSM R² = 0.72, ANN R² = 0.45). For BWG, model performance was weaker, and ANN’s apparent in-sample advantage over RSM (R² = 0.585 vs. 0.388 at 22–56 d) did not hold under leave-2-treatments-out validation (ANN R² = −12.7 vs. RSM R² = −0.24). Lastly, multi-objective optimization combining both models predicted stage-specific nutrient combinations. The results of this study provide empirical support and a methodological reference for establishing stage-specific nutritional standards for Hy-Line Brown male chicks.