Polymorphism of the Candidate Genes and Their Association with Egg Production Traits in Thai Native Chickens

Abstract
| Polymorphism was detected in the neuropeptide Y (NPY), dopamine receptor D2 (DRD2) and vasoactive intestinal peptide (VIP) genes, and their associations with egg production traits in 300 Thai native chickens were investigated. DNA was extracted from blood samples for genotyping using specific primers and restriction enzymes for each gene, and polymerase chain reaction-restriction fragment length polymorphism was used to identify the genotypes (PCR-RFLP). Three genotypes were found for each gene as BB, Bb and bb for NPY; TT, TC and CC for DRD2 and II, ID and DD for VIP. Genotype frequencies of NPY (range 0.13-0.58), DRD2 (range 0.06-0.55) and VIP (range 0.14-0.57) were reported. For the NPY gene, allele frequency of b (0.72) was greater than allele frequency of B (0.28), while for the DRD2 gene, allele frequency of T (0.26) was lower than allele frequency of C (0.74). I and D allele frequencies for VIP were 0.72 and 0.28, respectively. Statistical analysis results discovered significant associations between the three candidate genes (NPY, DRD2 and VIP). Egg production 270EN, 360EN and E_M of BB genotype were higher than bb genotype for the NPY gene (P < 0.01), while CC and TC genotypes of the DRD2 gene were associated with high 270EN, 360EN and E_M (P < 0.01). The DD genotype had higher 270EN, 360EN and E_M compared to ID and II genotypes, whereas other egg production traits were not influenced by the candidate gene. Results suggested that alleles of NPY, DRD2 and VIP genes showed potential as genetic markers for chicken egg production traits in Thai native chicken population selection programs.