Genet. Sel. Evol. 39 (2007) 711-729
DOI: 10.1051/gse:2007027

Predicting the consequences of selecting on PrP genotypes on PrP frequencies, performance and inbreeding in commercial meat sheep populations

Wing-Young N. Man^a, Ronald M. Lewis^b, Kay Boulton^c and Beatriz Villanueva<sup>a

a</sup>  Scottish Agricultural College, West Mains Road, Edinburgh, EH9 3JG, UK
^b  Department of Animal and Poultry Sciences (0306), Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
^c  Meat & Livestock Commission, Snowdon Drive, Milton Keynes, MK6 1AX, UK.

(Received 12 January 2007; accepted 6 June 2007; published online 6 December 2007)

Abstract - Selection programmes based on prion protein (PrP) genotypes are being implemented for increasing resistance to scrapie. Commercial meat sheep populations participating in sire-referencing schemes were simulated to investigate the effect of selection on PrP genotypes on ARR and VRQ allele frequencies, inbreeding and genetic gain in a performance trait under selection. PrP selection strategies modelled included selection against the VRQ allele and in favour of the ARR allele. Assuming realistic initial PrP frequencies, selection against the VRQ allele had a minimal impact on performance and inbreeding. However, when selection was also in favour of the ARR allele and the frequency of this allele was relatively low, there was a loss of up to three to four years of genetic gain over the 15 years of selection. Most loss in gain occurred during the first five years. In general, the rate of inbreeding was reduced when applying PrP selection. Since animals were first selected on their PrP genotype before being selected on the performance trait, the intensity of selection on performance was weaker under PrP selection (compared with no PrP selection). Eradication of the VRQ allele or fixation of the ARR allele within 15 years of selection was possible only with PrP selection targeting all breeding animals.

Key words: sire referencing / scrapie / prion / PrP selection / inbreeding

Correspondence and reprints: nicola.man@sac.ac.uk

© INRA, EDP Sciences 2007