Balancing essential amino acids in low-protein diets: Impacts on growth performance, amino acid transport, and cecal microbiota in yellow-feathered chickens

This study aimed to investigate the effects of partially removing essential amino acids (methionine, tryptophan, arginine, and isoleucine) from a low-protein diet on medium-speed yellow-feathered broilers aged 1-30 days. The evaluation focused on growth performance, physiological and biochemical indicators, amino acid transport, intestinal microbiota, and plasma free amino acid profiles. A total of 1,080 one-day-old yellow-feathered broiler hens were randomly assigned to six groups: a standard protein group (SD, CP 20.5%), a low-protein group (LP, CP 18%), and four amino acids groups that 20% reduction relative to the LP group in methionine (LP-Met), tryptophan (LP-Trp), arginine (LP-Arg), isoleucine (LP-Ile), respectively. Each group consisted of six replicates, with 30 chickens per replicate, the experiment lasted for 30 days. The results showed that the final body weight (BW) and average daily gain (ADG) of the LP group were significantly lower than those of the SD group (P < 0.05). The LP-Arg group exhibited the lowest FBW and ADG and the highest feed conversion ratio (P < 0.05), while the LP-Ile and LP-Met groups showed significantly higher protein deposition rates compared with the SD and LP groups (P < 0.05). The LP group exhibited elevated plasma level of triglycerides, blood urea nitrogen, and growth hormone, along with decreased levels of insulin-like growth factor-1 (P < 0.05). Reduction of Met or Trp decreased TG level compared with those observed in SD group, whereas reduction of Arg or Ile lowered BUN level (P < 0.05). The expression of the neutral amino acid transporter (B0AT) and excitatory amino acid transporter 3 (EAAT3) in the jejunum of the LP group was significantly upregulated (P < 0.05), with partial recovery observed after the reduction of Met, Trp, Arg, and Ile. Moreover, the LP group exhibited reduced α-diversity in the cecal microbiota and a decreased ratio of Firmicutes/Bacteroidetes (P < 0.05). The LP-Met group showed enrichment of beneficial bacteria such as Faecalibacterium, whereas the LP-Trp group was characterized by an increased the abundance of Firmicutes phylum (P < 0.05). The LP-Arg and LP-Ile groups exhibited a trend toward recovery of gut microbiota diversity. The LP group exhibited reduced levels of taurine and cysteine (P < 0.05), with differential responses observed among the amino acid reduction groups (e.g., elevated Thr in the LP-Met group and decreased Arg in the LP-Arg group). In summary, Arg reduction in LP diet had the most pronounced inhibitory effect on growth, whereas dietary Met and Ile reductions promoted greater protein deposition. These findings highlight the importance of precise amino acid balance to optimize production performance and health in yellow-feathered broilers fed low-protein diets.