Association between PrP genotypes and littersize and 135 days weight in Texel sheep

Susceptibility to scrapie is associated with polymorphisms in the ovine prion protein (PrP) gene. The polymorphisms at codons 136 (A to V), 154 (R to H) and 171 (Q to R, H) occur most frequently, where each letter represents the amino acid coded at the indicated codon. The VRQ allele is significantly associated with a high susceptibility to scrapie, while the ARR allelic variant is significantly associated with resistance to scrapie. The Dutch scrapie eradication strategy is based on selection for the genetically less susceptible variant ARR/ARR. The program indicates to use only ARR/ARR rams in the 2004 breeding season. In this study the association of PrP gene with performance traits was investigated. The data included 8919 genotyped Texel rams born from 1996 to 2000. The associations of PrP gene were evaluated with their estimated breeding value for littersize and 135 days weight. The results from this study indicated that selection for ARR/ARR genotype had a small positive effect on littersize, and a small negative effect on 135 days weight. The susceptible VRQ allele probably remained in the population due to positive association with littersize and 135 days weight. It is speculated that the wild type may have been favoured by selection due to associations with other performance traits, such as certain type traits. (C) 2003 Elsevier B.V. All rights reserved.