Growth-maturity-egg production trade-offs and candidate gene associations with egg-laying persistency in slow-growing...

Slow-growing Thai native chickens are valuable genetic resources for sustainable poultry production under tropical conditions, but their reproductive efficiency is constrained by trade-offs among growth, sexual maturity, egg production, and egg-laying persistency. This study investigated the multivariate structure and genetic basis of these trade-offs and evaluated trait-specific associations between candidate gene polymorphisms and estimated breeding values (EBVs).

Phenotypic, pedigree, and genotypic data were obtained from 563 female Pradu Hang Dum chickens across two generations. Growth performance, reproductive timing, egg production, and egg-laying persistency traits were recorded over a 365-day laying cycle. Principal component analysis (PCA) was used to characterize trait clustering. Genetic parameters and correlations were estimated using single- and bivariate animal models with average information restricted maximum likelihood procedures. Candidate gene polymorphisms in dopamine receptor D2 (DRD2), vasoactive intestinal peptide (VIP), melatonin receptor 1C (MTNR1C), and neuropeptide Y (NPY) were genotyped using polymerase chain reaction-restriction fragment length polymorphism and analyzed for associations with EBVs using linear mixed models.

PCA identified four principal components explaining 71.7% of the total phenotypic variance, clearly separating growth, sexual maturity, egg production output, and egg-laying persistency. Heritability estimates were high for birth weight (0.72), moderate for body weight at age at first egg (0.47) and persistency ratio (0.43), and low for cumulative egg number traits (0.08-0.12). Genetic correlations between egg number and persistency were strongly negative (-0.70 to -0.88). Candidate gene analyses detected significant genotype-dependent differences in EBVs for cumulative egg number at 360 days associated with DRD2, VIP, and NPY (p < 0.01), and MTNR1C (p < 0.05). Birds carrying the VIP DD genotype exhibited superior EBVs for egg number at 270 and 360 days, whereas the DRD2 CC genotype showed significantly higher genetic merit for egg number at 360 days than the TT genotype. In contrast, the NPY SS and MTNR1C AA genotypes were associated with reduced egg production. No significant associations were detected between these candidate genes and growth or persistency traits.

Egg-laying persistency represents a distinct biological dimension from growth and egg number in Thai native chickens. Incorporation of persistency into EBV-based multi-trait selection programs, together with the complementary use of candidate gene markers, may enhance long-term productivity and sustainability of indigenous chickens under tropical production systems. These findings provide a foundation for developing resilient dual-purpose breeding strategies that balance productivity and reproductive stability.