Intestinal Microbiota Composition in Fast and Slow Growing Broiler Chickens

Body weight is an important indicator of the overall health and production efficiency in broiler chickens. In broiler houses, body weight of chicks is variable despite the same genetics, hatching and feeding practices within a production system. The objective of this study was to investigate the intestinal microbiota and bile salt hydrolase (BSH) activity in slow and fast broiler chickens, which belonged to the 10th and 90th percentile body weight groups, respectively. A total of 300 Ross 308 broiler chickens (100 from three independent cohorts) were selected and mucosal samples from the jejunum, ileum, and cecum were collected at day of arrival, 11 and 25 (n = 450). Then, bacterial counts, 16s rRNA amplicon sequencing, species specific real-time qPCR, as well as BSH activity were analyzed. Results of bacterial counts showed no significant difference between slow and fast groups (P > 0.05), but they tended to be higher in the slow group in all measured bacterial groups in cecum. 16S rRNA amplicon sequencing revealed higher relative abundance of E. coli-Shigella (71.3-79.8%) at day of arrival, while the most abundant microorganisms at day 25 was Candidatus Arthromitus (slow: 44.5%; fast: 27.4%) in small intestine. qPCR results indicated significant differences in bacterial populations between the slow and fast groups, especially higher total bacteria, Enterococcus, and Clostridium cluster I in the slow group at day 25. BSH activity was higher in the slow group than the heavy group and correlation analysis highlighted associations between BSH activity, body weight, feed intake, body weight gain, and bacterial counts. We postulate that high total bacteria and Enterococcus abundance lead to high BSH activity, resulting in low feed intake and body weight gain, ultimately resulting in separation into slow and fast birds. The findings of this study contribute to understanding the relationship between gut microbiota, BSH activity, and host physiology in broiler chickens, with potential implications for poultry production.