PRION PROTEIN GENE POLYMORPHISMS AND BREEDING FOR SCRAPIE RESISTANCE IN THE BLACK-HEADED SHEEP

The goal of the study was to determine the frequency of prion protein (PrP) alleles and genotypes in a flock of the Black-headed sheep, carrying out the simulation of classical scrapie resistance breeding, as well as to investigate the association between PrP genotypes and lifetime prolificacy in the first, second, and third year of reproductive performance in this sheep. The study covered 95 sheep (79 ewes, 16 rams). Polymorphisms in codons 136, 154, and 171 of the prion protein gene were detected by means of PCR-RFLP method, using the following enzymes: BspHI (Pagl), BspDI and BseLl. Based on obtained frequencies of PrP alleles, the classical scrapie resistance mating simulation was carried out. The relationship between PrP genotype and lifetime prolificacy was analysed by the means of chi-square test of independence. Two alleles - ARR and ARQ, and two genotypes - ARR/ARR and ARR/ARQ were identified in the investigated sheep. The most frequent was ARR allele (82.6%) in both ewes (81%) and rams (90.6%). The study on the simulation of classical scrapie resistance breeding revealed a continuous growth of frequency of ARR/ARR individuals, starting from generation F1. The result of chi-square test did not confirm the hypothesis of association between PrP genotype and lifetime prolificacy, which suggests that classical scrapie resistance breeding should not have an influence on reproduction traits of Black-headed sheep, at least on the analysed ones.