Associations Of Nucleotide Variation In Parathyroid Hormone Gene With Eggshell Quality In Fengda Layer FD Line

Parathyroid hormone （PTH）, an alkaline polypeptide hormone released by the parathyroid gland of animals, plays a key role in regulating the metabolism of calcium and phosphate in vertebrates. In poultry, the PTH associates with eggshell calcification and is a improtant bioactive factor that affacts eggshell quality. In this study, PCR-SSCP was adopted to identify the SNP in PTH encoding region of Fengda layer FD line, and the associations between SNP and egg quality traits including eggweight, eggshell weight, egg shape index, eggshell breaking strength, percent of eggshell, levels of serum calcium, serum phosphate, and serum PTH at 28 and 40 wks of age were analyzed, repectively.The nucleotide Polymorphism test showed that there was a single nucleotide mutation, A2205G （GenBank accession no.:NC₀06092.2）, in the exon-3 of chicken PTH. The mutation caused the codon for lysine in the 28th amino acid of mature chicken PTH changing from AAA to AAG （synonymous mutation）. The allelic frequencies for A and G were 0.67 and 0.33, respectively; the genotypic frequencies of AA, AG, and GG were 0.426, 0.489, and 0.085, respectively. x2test showed that distribution of genotypes was in Hardy-Weinberg’s equilibrium （x2= 3.54< x20.05（2）= 5.99）.Association between genotypes and eggshell traits analysis showed that the A2205G did not affact all the egg quality traits at 28 wks of age （P> 0.05）, which may owe to the initial stage of laying and unstable quality of eggs. At 40 wks of age, the egg weight and egg shape index did not differ among genotypes （P> 0.05）, however, the eggshell percentage and breaking strength for genotype GG and AG were greater（P< 0.05） than AA, respectively, indicating that the A2205G in PTH may be regarded as a molecular marker for eggshell strength. Biochemical index analysis revealed that the total serum calcium for genotype GG was higher than genotype AA and AG by 11.8% and 10.1%, respectively; the serum phosphate for genotype GG was greater than genotype AA and AG by 16.7% and 12%, respectively, and For serum PTH, genotype GG was nearly 30% higher than genotype AA. These facts suggested that the SNP affacted eggshell traits via regulating the level of serum calcium and PTH.In conclusion, the A2205G in PTH significantly associated with the eggshell percentage and breaking strength in Fengda layer FD line, and the SNP had the potential of utilization in molecular breeding for eggshell traits.