The Veterinary Record 159:473-479 (2006)
© 2006 British Veterinary Association
PrP genotype progression in flocks participating in the National Scrapie Plan for Great Britain
R. G. Warner, MA, DPhil1,
D. Morris1 and
M. Dawson, BVetMed, MSc, MRCVS1
1 National Scrapie Plan Administration Centre, State Veterinary Service,
Whittington Road, Worcester WR5 2SU
The National Scrapie Plan (NSP) for Great Britain is a voluntary
scheme that, through PrP genotype testing and restricted breeding, aims to
reduce the risk of scrapie in the national sheep flock. To gauge the progress
in member flocks and within breeds, the genotype profile of successive crops
of ram lambs was monitored between 2002 and 2004. In each of the 11 most
frequently sampled breeds, the proportion of ram lambs testing in the most
resistant genotype category (NSP type 1: ARR/ARR)
increased, and there was a reduction in the proportion of genotypes associated
with the highest disease risk, that is X/VRQ, where X is an allele
other than ARR. Changes in the proportion of ram lambs testing for
ARR-heterozygous genotypes (NSP type 2: ARR/X, where X
is not VRQ) appeared to be influenced by whether the sheep were
hill breeds or non-hill breeds. In each of six frequently sampled hill breeds
these genotypes expanded, in relative terms, whereas they declined in four of
five prominent lowland/crossing breeds. The proportion of ram lambs that
carried neither ARR nor VRQ (NSP type 3)
declined consistently in the top 11 breeds, but there was little change in the
ARR/VRQ genotype (NSP type 4). Among individual flocks
that had ram lambs tested in all three years 2002 to 2004, the majority
experienced an increase in the proportion testing ARR/ARR, and of
those that had VRQ ram lambs in 2002, most recorded a decrease in
their frequency by 2004.
Copyright © 2006 British Veterinary Association
