Exploring Growth Pattern and Candidate Genes for Chicken Spur

The chicken spur is a bony structure located on the tarsometatarsus and extending posteriorly. Because its length increases with age, it has become an important indicator of rearing duration and a trait of interest in high-quality chicken breeding. The developmental pattern of the chicken spur and its underlying genetic mechanisms remain poorly understood. In this study, Nandan-Yao chickens were used to investigate spur growth and development. Phenotypic measurements and X-ray imaging were performed to characterize spur growth, and RNA sequencing was used to identify candidate genes associated with spur length. Candidate genes were further evaluated by tissue expression profiling and RNA interference. The results showed that spur length was not significantly associated with body weight, body size, or laying traits (p > 0.05). In roosters, sperm motility and ln(T/E2) were significantly higher in the long spur group than in the short spur group (p < 0.05). X-ray imaging and gene expression analysis indicated that the chicken spur is a bony structure that develops through an endochondral ossification pattern, with the ossification center appearing at approximately 15 weeks of age in Nandan-Yao chickens. TENM2 was identified as a key candidate gene associated with spur development, and functional analysis suggested that it may be involved in this process through the BMP signaling pathway. These findings provide a basis for understanding the developmental pattern and genetic mechanisms of chicken spur formation and support the potential breeding value of spur traits.