Spatiotemporal dynamics of bile acid profiles in broilers from hatch to market age.

Systematic research on the dynamic distribution of bile acids (BAs) throughout the enterohepatic axis in broilers remains limited. Therefore, this study aimed to elucidate the spatiotemporal dynamics of the BA pool in broilers from hatching to market age. Newly hatched broiler chickens were reared under standard conditions for 42 days. At the end of each week, six birds were randomly selected to collect samples for the determination of BAs. The results revealed a clear spatial concentration gradient of total bile acids (TBAs). Bile exhibited the highest TBA concentration (approximately 10⁸ ng/mL), followed by small intestine and colorectum (approximately 10⁶-10⁷ ng/g DM), liver (approximately 10⁵-10⁶ ng/g DM), cecum (< 10⁵ ng/g DM), and serum (approximately 10³ ng/mL). The ileum and cecum were identified as active sites for microbial BA metabolism. Microbial deconjugation was primarily observed in the ileum. There was a significant increase in the proportion of unconjugated BAs, rising from 48.35% to 83.92% by week 3 (P < 0.01). Concurrently, microbial 7α-dehydroxylation was prevalent in the cecum. The proportion of secondary BAs, primarily lithocholic acid (LCA), increased progressively, with a significant rise observed by week 3 (P < 0.05). These findings indicate that week 3 may be a critical period for the functional maturation of BA-metabolizing microbiota. Principal component analysis (PCA) and permutational multivariate analysis of variance (PERMANOVA) analyses confirmed significant spatial heterogeneity in BA profiles across the enterohepatic axis (P = 0.001). The liver, bile and serum maintained stable profiles dominated by taurine-conjugated primary BAs. Limited microbial deconjugation occurred in the duodenum and jejunum. The cecum consistently formed a distinct cluster characterised by a significantly higher proportion of secondary BAs. Notably, no significant difference was found between the BA profiles of the ileum and colorectum (P > 0.05). This finding highlights a species‑specific aspect of avian digestive physiology, differing from the clear separation between ileal and colon bile acid profiles typically seen in mammals.