Effect of Prolactin Gene Polymorphisms on Egg Weight of White Leghorn and Hy-line Brown Laying Hen Strains

This study was conducted at Poultry farm and Poultry Physiology laboratory Animal Resources Department / College of Agriculture / The University of Baghdad during a period from 26/September/2013 to 1/June/2014 to find out the association of prolactin (PRL) gene polymorphisms with egg weight of laying hens. Two strains of laying hens, White Leghorn (n=100) and Hy-line Brown (n=60) were used in this study and reared in individual cages Blood samples were collected from a brachial vein at 41 weeks of age. The PRL gene polymorphisms were determined using PCR-RFLP technique and Alul restriction enzyme. Two alleles C and T and three genotypes wild type CC (homozygous), heterozygous CT and mutant TT (homozygous) have been got. The size of the target gene fragment was 439 bp. A significant (p 0.05) difference was showed in the Brown strain between genotypes CC and TT, the genotype CC was higher than TT in egg weight (EW) at 34 week of age, in White strain there was a significant (p 0.05) differences between CC and CT, also, CC with TT genotypes in EW at 30 week of age. The T allele frequency was 0.66, whereas, C allele frequency was 0.34 for Brown strain. In White strain, the C allele frequency was 0.98, whereas T allele frequency was 0.02. The distribution percentage of polymorphism of PRL gene in Brown strain were 56.60, 37.74 and 5.66 % for CT, TT and CC genotype respectively, whereas, the distribution percentage of polymorphism of PRL gene in White strain were 97.75, 1.12 and 1.12 % for CC, CT and TT genotype respectively, and the differences among percentages was significant (p 0.01). The allele frequency and distribution percentage of polymorphism for PRL gene was measured according to Hardy-Weinberg equilibrium.