CONCLUSION

This study demonstrated that egg-laying persistency is a partially independent biological and genetic dimension in Thai native chickens, distinct from growth, sexual maturity, and cumulative egg production. PCA separated growth, maturity, egg production, and persistency traits into different components, while genetic analyses showed moderate heritability for BW0, AFE_WT, and PR, but low heritability for cumulative egg number traits. Strong negative genetic correlations between EN270, EN360, and persistency traits indicated that higher cumulative egg production does not necessarily reflect stable long-term laying performance in this population.

From a practical perspective, these findings suggest that breeding programs for Thai native chickens should not rely solely on cumulative egg number or early growth traits. Instead, multi-trait EBV-based selection indices should include egg-laying persistency to improve long-term reproductive stability while maintaining productivity under tropical conditions. Candidate gene polymorphisms in DRD2, VIP, NPY, and MTNR1C were associated mainly with cumulative egg number, particularly EN360, suggesting that these markers may serve as supplementary tools for improving long-term egg yield rather than as primary predictors of persistency.

The strength of this study lies in its integrated approach, combining phenotypic trait clustering, animal-model genetic parameter estimation, and EBV-based candidate gene association analysis over a 365-day laying cycle in a slow-growing indigenous chicken population. However, the findings should be interpreted with caution because persistency traits were based on simplified ratio-derived indicators, egg number traits showed low heritability, and deviations from Hardy–Weinberg equilibrium were observed for the VIP and NPY loci. In addition, the functional effects of the investigated polymorphisms were not experimentally validated.

Future studies should use longitudinal egg production records, larger multi-generation populations, genomic selection approaches, and functional validation of candidate variants to clarify the biological mechanisms underlying laying persistency. Overall, incorporating egg-laying persistency with cumulative egg production and candidate gene information may support the development of resilient, productive, and sustainable Thai native chicken lines for tropical low-input production systems.