Relationship between the insertion/deletion polymorphism within the promoter and the intron 1 sequence of the PRNP gene and milk performance traits in cattle

Current studies on the prion protein (PRNP) gene polymorphism focus primarily on the causative mutations that influence BSE susceptibility in cattle. The specific genetic structure determined by the insertion/deletion (indel) polymorphism within the 23 bp promoter sequence and the 12 bp intron 1 sequence of the PRNP gene, and its genomic location suggest that this polymorphism can be a potential QTL marker. The objective of the present study was to determine whether the indel polymorphism within the promoter sequence (23 bp) and the intron 1 sequence (12 bp) of the PRNP gene can be used as a factor differentiating the values of milk performance traits. The experimental materials comprised 285 primiparous Polish Holstein-Friesian cows, daughters of two dihybrid (23ins-12ins/23del-12del) sires (progeny of sire 1 - 149 cows, progeny of sire 2 - 136 cows). The following milk performance traits were analysed: milk yield, milk fat yield, milk protein yield, fat and protein contents of milk during the first 305-day lactation. The polymorphism in the promoter region (23 bp) was found to have a significant (P = 0.040) effect on protein yield and a highly significant (P = 0.007) effect on the protein content of milk. The highest values of these traits were noted in 23 ins/del heterozygotes and the lowest in 23 del/del homozygotes. There was an interrelation between diplotype variants and the concentrations of milk components. The protein content of milk was highly significantly (P = 0.007) higher in 23ins-12ins/23del-12del heterozygotes and significantly (P = 0.028) higher in 23ins-12ins/23ins-12ins homozygotes, compared to 23del-12ins/23del-12del cows. 23ins-12ins/23del-12del heterozygotes were also characterized by a significantly (P = 0.046) higher fat content of milk, in comparison with 23del-12del/23del-12del homozygotes.