Prediction of Genetic Resistance for Scrapie in Ungenotyped Sheep Using a Linear Animal Model

Abstract

Selection based on scrapie genotypes could improve the genetic resistance for scrapie in sheep. However, in practice, few animals are genotyped. The objectives were to define numerical values of scrapie resistance genotypes and adjust for their non-additive genetic effect; evaluate prediction accuracy of ungenotyped animals using linear animal model; and predict and assess selection response based on estimated breeding values (EBV) of ungenotyped animals. The scrapie resistance (SR) was defined by ranking scrapie genotypes from low (0) to high (4) resistance based on genotype risk groups and was also adjusted for non-additive genetic effect of the haplotypes. Genotypes were simulated for 1,671,890 animals from pedigree. The simulated alleles were assigned to scrapie haplotypes in two scenarios of high (SRh) and low (SRl) resistance populations. A sample of 20,000 genotyped animals were used to predict ungenotyped using animal model. Prediction accuracies for ungenotyped animals for SRh and SRl were 0.60 and 0.54, and for allele content were from 0.41 to 0.71, respectively. Response to selection on SRh and SRl increased SR by 0.52 and 0.28, and on allele content from 0.13 to 0.50, respectively. In addition, the selected animals had large proportion of homozygous for the favorable haplotypes. Thus, pre-selection prior to genotyping could reduce genotyping costs for breeding programs. Using a linear animal model to predict SR makes better use of available information for the breeding programs.

Genetic Parameter Estimation and Selection for Resistance to Gastrointestinal Nematode Parasites in Sheep—A Review

“…The trait most commonly used as a measurement of GIN resistance in sheep is FEC [18,30,31]. This trait is heritable, repeatable, and a reliable parameter to measure the animals' resistance [17,33]. The number of eggs counted in the faeces is used as an estimate for the number of female worms within the host and the worm's fecundity capacity [17,31].…”

Genomic Regions Associated with Resistance to Gastrointestinal Nematode Parasites in Sheep—A Review

“…Researchers have confirmed differences in the immune response among GIN-infected animals, which can be attributed to genetic variations among animals [20][21][22]. By discovering and understanding the underlying genetic regions contributing to the variation in individual immune response to GIN infection and resistance to GIN infection in sheep, breeding strategies can be tailored to mitigate the impact of these parasites [22].…”