Prediction of prion protein genotype and association of this genotype with lamb performance traits of Suffolk sheep1,2

Abstract

ABSTRACT:The association of the prion protein (PrP) gene with susceptibility to scrapie has formed the basis of selection programs aimed at eradicating the disease from sheep populations. Animals are genotyped for the PrP gene and those with the less susceptible genotypes are selected. The objectives of this study were to determine the effectiveness of predicting PrP genotypes by using information from relatives and to investigate the association of the PrP genotype with lamb performance traits in Suffolk sheep. Data were obtained from a scrapie-affected flock maintained in Scotland. A total of 643 were animals genotyped at codon 171 of the PrP gene with 2 alleles, R and Q. The genotypes of these animals were used to predict the genotypes of 5,173 nongenotyped animals in the same flock using segregation analysis. The genotype of nongenotyped animals was predicted from the probabilities for each possible genotype; further, an overall index for each animal was calculated to reflect the accuracy of prediction. Association analyses of the PrP gene (using animals with both known and inferred genotypes) with BW at birth, at weaning (56 d), and at 150 d, and for backfat and muscle depths at 150 d of age were carried out. A linear mixed model with random direct and maternal additive genetic effects, maternal permanent and temporary environmental effects, and year of birth was tested, and the most appropriate model was used for each trait. The expected number of Q alleles carried (from 0 to 2) by each animal was calculated and used in the model as a linear and quadratic covariate to test for associations with possible additive and dominance PrP gene effects, respectively. Results showed that the genotypes of relatively few animals (235) were inferred with certainty (compared with the 5,173 nongenotyped animals). Approximately 25% of the 5,173 predicted genotypes were inferred with a genotype probability index of 50% and greater. There was no significant association of the PrP gene with any of the performance traits studied (there were no significant additive or dominance effects). Such was the case whether data on animals with known or with both known and predicted genotypes were considered. It can be concluded that selection for PrPresistant alleles in Suffolk sheep is unlikely to affect performance directly.

Emerging prion disease drives host selection in a wildlife population

“…Previous research in the Wisconsin CWD zone has indicated that deer experience the same harvest-related mortality pressure regardless of CWD status (Grear et al 2006). However, one study suggested higher mortality rates in scrapie-resistant lambs (Sawalha et al 2010). However, there is scant evidence suggesting that the PRNP gene would be under selective pressure for reasons not related to disease.…”

“…Scrapie-resistance breeding programs for sheep in the European Union have examined fitness parameters associated with the PRNP genotype and found no evidence of negative association between TSE-resistant genotypes and reproduction or performance traits (Sweeney and Hanrahan 2008). However, one study suggested higher mortality rates in scrapie-resistant lambs (Sawalha et al 2010). To be conservative, we used our population model to evaluate potential deviations from our assumption of similar baseline fawn survival rates between genotypes.…”

Expanding Possibilities for Intervention against Small Ruminant Lentiviruses through Genetic Marker-Assisted Selective Breeding

“…The concern was noted very early that selection for scrapie resistance or susceptibility was only one component of a breeding program and would not be as valuable if tradeoffs had to be made between scrapie susceptibility and other production traits [120]. Accordingly, a large body of research addressed potential genotypic association with production traits including reproductive performance, wool characteristics, growth, body type, and dairy ability, among others [123,124,125,126,127,128,129,130,131,132,133]. Work was even done examining susceptibility to small ruminant lentiviruses [86].…”

Pathogen-mediated selection in free-ranging elk populations infected by chronic wasting disease

“…However, this outcome is contingent on the assumption that the L allele does not have any negative fitness-related impacts. This topic has not been sufficiently investigated in free-ranging cervids; some evidence of PRNP-related impacts on fitness has been observed in domestic sheep, a species affected by the transmissible spongiform encephalopathy scrapie (24)(25)(26). Our results indicate that the M allele is consistently overrepresented in populations without CWD; the majority of individuals were MM homozygotes (≥0.69) and M allele frequency ranged from 0.83 to 0.96.…”