Despite the possibly minor involvement of a single gene (prnp), what makes sheep susceptible to scrapie remains completely unknown. Government insistence that susceptibility only dependents on the prnp gene is false but is also a dangerous assumption. This present assumption may very well change in the near future. Limiting the national flock to one of limited genetic diversity will, in the next two years, cause the loss of both essential diversity and unique genetic material, possibly forever.
Several breeds have sufficient homozygous sheep, but often in only a few blood lines. Inbreeding will go up, often in association with deteriorating quality and undesirable characteristics. Breed traits associated with the ARQ/ARQ genotype will be lost. Despite the expert generalisations to the contrary, some breeds of sheep with this scrapie-susceptible genotype have never shown any sign of scrapie. These breeds should be used for breeding without any objection.
ARR/ARR sheep do not develop clinical signs but that does not mean that they do not carry the ‘Scrapie agent’. Breeding for scrapie resistance could well turn out to be a disaster, for eliminating genetic diversity exposes a population to pathogens that are unknown or that mutate from known pathogens.