J Vet Sci.  2013 Mar;14(1):45-51. 10.4142/jvs.2013.14.1.45.

Trends in genotype frequency resulting from breeding for resistance to classical scrapie in Belgium (2006~2011)

• Dobly A
• Van der Heyden S
• Roels S

• KMID: 1482812
• DOI: http://doi.org/10.4142/jvs.2013.14.1.45

Abstract

In sheep, susceptibility to scrapie is mainly determined by codons 136, 154, and 171 of the PRNP gene. Five haplotypes are usually present (ARR, ARQ, ARH, AHQ, and VRQ). The ARR haplotype confers the greatest resistance to classical scrapie while VRQ renders animals most susceptible. In 2004, the European Union implemented a breeding program that promotes selection of the ARR haplotype while reducing the incidence of VRQ. From 2006 to 2011 in Belgium, frequency for the ARR/ARR genotypes increased from 38.3% to 63.8% (n = 6,437), the ARQ haplotype diminished from 21.1% to 12.9%, and the VRQ haplotype decreased from 2.0% to 1.7%. The status of codon 141, a determinant for atypical scrapie, was also evaluated. Out of 27 different breeds (n = 5,163), nine were abundant. The ARR/ARR frequency increased in eight of these nine major breeds. The selection program has had a major impact on the ARR haplotype frequency in Belgium. However, the occurrence of atypical scrapie represents a critical point for this program that warrants the continuous monitoring of scrapie. Additionally, genotype frequencies among the breeds varied greatly. Texel, a breed that is common in Belgium, can still be selected for due to its average ARR frequency.

Keyword

genetics; prion diseases; PrP; ruminant; transmissible spongiform encephalopathy

MeSH Terms

Animals
Belgium
*Breeding
Female
*Genetic Predisposition to Disease
Genetic Variation
*Genotype
Male
Scrapie/*genetics
Sheep

Figure

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  Fig. 1 Changes in genotype frequencies during the breeding program in Belgium from 2006 to 2011. The genotypes are grouped into five categories of decreasing resistance to scrapie.

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  Fig. 2 Changes in the five haplotype frequencies during the breeding program in Belgium from 2006 to 2011.

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  Fig. 3 The influence of birth year on haplotype frequencies for the sheep analyzed. Due to their limited numbers, animals born before 2000 were grouped together. The number of sheep analyzed is indicated below each birth year.

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