Genetic Selection for High Body Weight Reshapes Gastrointestinal Structure and Microbiota in Lueyang Black-Boned Chickens

Lay Summary Genetic selective breeding has greatly increased the growth rate of modern chickens, improving global food production efficiency. However, its effects on the digestive system are not fully understood. In this study, we compared a traditional chicken line with a line selectively bred for high body weight. Growth was monitored from hatching to adulthood, and digestive organ development and gut microbial communities were examined at maturity. Chickens selected for higher body weight grew faster in later stages and converted feed more efficiently. They showed larger digestive organs and improved intestinal structure, suggesting enhanced capacity for digestion and nutrient absorption. Distinct differences were also observed in microbial communities across intestinal regions. These microbial patterns were associated with greater potential for nutrient utilization, while immune-related functions appeared reduced. Overall, long-term selection for high body weight was associated with adaptive changes in both digestive organs and gut microbial composition, providing insight into how breeding strategies influence gut biology and production performance.