Phenotype and genetic characterization of the egg-laying related traits in indigenous Beijing-You chickens

Egg is one of the most accessible sources of animal protein, and indigenous chicken breeds have gained increasing attention in recent years due to consumers' growing demand for diversified egg products. Genetic improvement of these breeds has become critical for enhancing the economic sustainability. This study aimed to characterize individual laying patterns and estimate genetic parameters for egg production, oviposition intervals, and other clutch-related traits in indigenous Beijing-You chickens, providing effective indicators for within breed selection. Egg production records were collected over 23 days (33-35 week) to characterize individual laying patterns and calculate oviposition intervals. Additionally, genetic parameters for age at first egg (AFE), egg number (EN), and average clutch length (ACL) were estimated using individual laying records until 43 weeks of age and 61 weeks of age, respectively. Variance-covariance components were estimated using a multivariate animal model in ASReml-R 4.2 through restricted maximum likelihood (REML), from which genetic and phenotypic correlations were derived. Heritability estimates were obtained separately with a univariate equivalent of the model. Results showed that the daily oviposition peak occurred between 10:00 and 13:30, accounting for 34 % of total daily egg production. Genetic parameter estimates revealed heritabilities of 0.29 and 0.16 for EN until 43 weeks of age (EN43) and EN61, respectively, while the overall average OP was 26.46 hours with a heritability of 0.40. Heritabilities for other traits ranged from 0.06 to 0.69. OP exhibited extremely high genetic correlation with the EN during the 23-days. AFE and ACL43 emerged as optimal selection criteria due to their elevated heritability estimates and strong genetic correlations with total egg production through 61 weeks of age. Notably, a significant negative genetic correlation emerged between OP and fertilization rate during concurrent measurement periods. In all, this study indicates that OP is a promising selection trait and its combination with AFE and ACL may offer new insights into the breeding for higher egg production of Beijing-You chickens.