Breeding programmes for elimination of alleles in rare breeds: scrapie in the Netherlands

Small populations often suffer from genetic defects. Single gene defects can be eliminated by selection for specific alleles, but then there is a risk of increased inbreeding with associated loss of genetic variation, inbreeding depression and increased frequency of other genetic defects. Here we investigate special breeding programs for scrapie resistance with inbreeding restriction. A ram circle, where each flock uses rams from another flock, is most suited for situations where pedigrees are unknown and animals are herded in large flocks. Inbreeding minimization with optimal contribution theory is most suited when pedigree records are available and a few breeders provide most rams for the whole population. Both schemes considerably reduced inbreeding rates in the Kempisch Heideschaap and in the Mergellande