Appetite gene expression and gut microbiota in broiler chickens with varying body weights: a new perspective on flock uniformity

Flock uniformity is critical in the broiler industry to ensure consistent processing yields, optimize feed efficiency, and reduce economic losses associated with size variation. The purpose of this study was to investigate differences in appetite-related gene expression and microbiota in broiler chickens with different BW. On D 18, birds were categorized into three BW groups within a flock: small (S; 300 to 400 g), medium (M; 400 to 500 g), and large (L; 500 to 600 g), with 8 replicates per group. Data were analyzed by ANOVA with post hoc Tukey's test ( P < 0.05). The S group had significantly higher mRNA expression of taste receptor type 2 member 7 (T2R7; bitter taste receptor) in the upper palate and cholecystokinin (CCK) in the brain compared to the L group. In contrast, the S group had significantly lower expression of neuropeptide Y receptor Y1 (NPYY1) and NPYY2 in the brain, and taste receptor type 1 member 1 (T1R1; umami taste receptor) in the duodenum compared to the L group. No differences were observed in duodenal brush border enzyme activities ( P > 0.05). The L group showed higher serum endotoxin levels compared to the S group ( P < 0.05). No significant differences in phylum-level taxonomic abundance were observed in the cecal microbiota ( P > 0.05). At the family level, the M group had a higher relative abundance of the family Bacillaceae compared to the L group ( P < 0.05). Alpha diversity showed no significant differences ( P > 0.05). Beta diversity analyses (Jaccard and unweighted UniFrac) revealed distinct microbial community structures among the different BW groups with visual separation of the S group, and unweighted UniFrac distances confirmed significant group differences ( P < 0.05). In conclusion, BW variation within the flock was associated with differences in appetite-related gene expression, while differences in cecal microbiota and gut function were observed but their functional relevance in relation to BW variation remains unclear under the present conditions.