Identification of Haplotypes in Promoter of Prolactin Gene and Their Effect on Egg Production and Quality Traits in Layer Chicken

Abstract

Expression of prolactin hormone is a crucial event in regulating egg production in chickens for which promoter plays the vital role in expressing the prolactin gene. The objective of the present study was to identify haplotypes in the prolactin promoter and their effects on egg production and egg quality traits in White Leghorn chicken. Single stranded conformation polymorphism followed by sequencing was conducted to explore polymorphism at 561 bp promoter of prolactin gene. The effect of haplotype combinations on egg production and quality traits were estimated following general linear model technique. The expression of prolactin by different haplogroups was quantified by qPCR. Total 28 haplotypes were found in White Leghorn chicken of which h1 haplotype possessed the highest frequency of 0.46 and h8, h14, h16, h25, h26, and h28 haplotypes had the lowest frequency (0.1%). The egg production up to 52 and 64 weeks of age were found to be significantly (p < 0.05) associated with haplotype combinations where the highest 52-w (52 weeks) egg production was found in animals with h1/h22 combination and the lowest production was observed in the birds with h1/h2 haplogroup. The haplotype combinations had the significant effect (p < 0.05) on Haugh Unit, yolk index and albumen weight at 40 weeks of age; Haugh Unit and albumen weight at 52 weeks of age and Haugh unit, yolk weight and yolk percentage at 64 weeks of age. The prolactin expression in h1/h22 birds was found to be the lowest and in h1/h5 birds to be the highest. The prolactin expression showed significant effect on 52-w egg production and albumin weight at 52 weeks age. In conclusion, it may be stated that the prolactin promoter was highly polymorphic and had the significant association with egg production and quality traits in White Leghorn chicken.

Keywords:

• Association
• Chicken
• Expression
• Haplotype
• Prolactin promoter

Notes

EP52 = Egg production from egg at first lay to 52 weeks of age; EP64 = Egg production from egg at first lay to 64 weeks of age; HU40 = Haugh unit at 40 weeks of age; YI40 = Yolk index at 40 weeks of age; AW40 = Albumin weight at 40 weeks of age; HU52 = Haugh unit at 52 weeks of age; AW52 = Albumin weight at 52 weeks of age; HU64 = Haugh unit at 64 weeks of age; YW64 = Yolk weight at 64 weeks of age; YP64 = Yolk percentage at 64 weeks of age. Values within parenthesis are the animal number within a haplogroup.

Different superscripts column-wise indicate significance at P < 0.05.