Breeding for resistance to scrapie: Detection of polymorphisms in the prion protein gene in German sheep breeds

Scrapie is a fatal neurodegenerative disease of sheep and goats belonging to the group of transmissible spongiform encephalopathies (TSE). TSEs are characterised by distinctive pathology, the involvement of a hostencoded prion protein (PrP) in disease development and genetic control of susceptibility. Polymorphisms in three different codons of the ovine prion protein (PrP) gene (136, 154, 171) determine the scrapie susceptibility of individual animals. In a number of countries, studies of PrP genotypes linked to scrapie revealed the resistance of homozygous prP ARR /PrP animals and the high risk of animals carrying PrP* and prp ARQ alleles in scrapie-affected areas. Therefore, scrapie in sheep can be controUed by breeding for the resistant PrP /PrP genotype. We genotyped 1506 German breeding sheep from 16 different breeds in Northern Germany. At least five PrP allelic variants were found among these breeds and the greatest variability within the PrP gene was encountered in Texel sheep, where 14 different PrP genotypes were found. In important meat breeds like Suffolk, German Whiteheaded Mutton, and German Blackheaded Mutton the PrP allele was predominant. In these breeds the expected time of a few generations for breeding of scrapie-resistant pedigree flocks seems to be a feasible Option. For the examined Texel sheep, the German Merino, the German milk and the German land sheep breeds the frequency of the PrP allele was much lower. For several breeds no homozygous rams were available for breeding purposes at the time. The breeding strategy therefore depends on the number of PrP heterozygous rams.