Association of polymorphism in the prolactin promoter and egg quality traits in laying hens.

Single strand conformation polymorphism analysis and DNA sequencing was performed in White Leghorn hens to explore the polymorphisms present in the promoter of the prolactin gene. The effects of different genotypes on egg production and quality traits were determined, and expression of the prolactin gene in different genotypes was quantified by real time-PCR. Five genotypes and four alleles at each of two Fragments of the promoter were found, of which the FG genotype in Fragment 1 and the PQ genotype in Fragment 2 were the most predominant genotypes. The genotypes of Fragment 1 had significant effects (P < 0·05) on Haugh unit, albumen weight, albumen percentage and shell percentage at 40 weeks of age; egg weight and yolk index at 52 weeks of age; and egg weight at 64 weeks of age. Prolactin expression in the genotypes of Fragment 1 differed significantly and GH genotyped birds had the highest level of expression. The genotypes of Fragment 2 did not show any significant differences of expression. It was concluded that the prolactin gene promoter was highly polymorphic, and had significant effects on egg quality traits in White Leghorn hens.