PrP genotype frequencies in German breeding sheep and the potential to breed for resistance to scrapie

Genetic susceptibility to scrapie is associated with polymorphisms in three different codons of the ovine prion protein (PrP) gene (136,154,171). Stud ies of PrP genotypes linked to scrapie have revealed the resistance of homo zygous PrPARR/PrPARR animals and the high risk of PrPVRQ/PrPVRQ and PrPVRQ/ PrPARQ animals in scrapie-affected flocks. The selection of PrPARR/PrPARR g enotypes may therefore provide a strategy for controlling clinical scrapie. The genotypes of 1361 German breeding sheep from 15 different breeds in no rthern Germany were determined. Apart from the wildtype allele PrPARQ, at l east four mutually exclusive allelic variants were found. The greatest vari ability within the PrP gene was encountered in texel sheep, in which 14 PrP genotypes were found. in the important meat breeds, Suffolk, German whiteh eaded mutton and German blackheaded mutton, the PrPARR allele was predomina nt, and in these breeds the breeding of scrapie-resistant pedigree flocks w ithin four generations seems to be a feasible option. In the texel sheep, t he German merino, the German milk and the German land sheep breeds, the fre quency of the PrPARR allele was much lower, and in several breeds no homozy gous rams were available for breeding purposes. in these breeds the breedin g strategy would depend on the number of heteroxygous rams available, but r esistant pedigree flocks could be achieved within nine generations.