The impact of the National Scrapie Plan on the PRNP genotype distribution of the British national flock, 2002–2012

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In order to determine the PRNP genotype distribution of the sheep population and to assess the impact of the National Scrapie Plan, a total of 9972 brain samples were collected between January 2012 and April 2013 from sheep sampled under the TSE active surveillance programme in Great Britain. Genotype frequencies observed were ARR/ARQ (29.5 per cent), ARR/ARR (28.6 per cent), ARR/AHQ (10.9 per cent), ARQ/ARQ (9.8 per cent) and AHQ/ARQ (7.2 per cent). Of the remaining possible genotypes, none accounted for more than 5 per cent of the sheep sampled. ARR was the most frequent allele (52.3 per cent), followed by the wild-type ARQ (30 per cent), AHQ (11.3 per cent), VRQ (3.4 per cent) and ARH (3 per cent). There has been a positive but limited effect of the breeding for resistance schemes within Great Britain on the genotype distribution in the sheep national flock. The dissemination of the resistant alleles has proven to have been less noticeable than in the breeding flocks. The risk of atypical scrapie remains very similar to that in 2002. Significant differences were observed in the genotype profiles of the abattoir survey and fallen stock survey samples. It would be advisable to promote best practice among farmers to consolidate the level of genetic resistance in their flocks and to set up a national flock genotype monitoring programme in partnership with the industry.

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