Scrapie resistance and production traits in Rambouillet rams: ram performance test 2002-2006

Sheep possessing alleles for the prion protein with glutamine (Q) or histidine, both reported as Q, at codon 171 are highly susceptible to scrapie. Incidence of scrapie infection is rare when animals possess at least one allele for arginine (R) at codon 171. The current USDA APHIS scrapie eradication program utilizes genotyping for alleles that confer resistance to scrapie. Although it has not been a criterion of registration, genotyping has been utilized in the University of Wyoming Ram Performance test since 2002. Performance test records from 2002 to 2006 (n=518) were analyzed to determine if any production loss or benefit was associated with scrapie resistance in rams. Performance of rams with scrapie resistant genotypes was equal to or better than scrapie susceptible rams. Based on test performance as an acceptable indicator of sire superiority, selection for rams with scrapie resistant genotypes should not negatively impact flock performance.     

Estimation of genetic parameters for wool fiber diameter measures.

Genetic and phenotypic correlations and heritability estimates of side, britch, and core diameters; side and britch CV; side and britch diameter difference; and clean fleece weight were investigated using 385 western white-faced ewes produced by 50 sires and maintained at two locations on a selection study. Data were analyzed using analysis of variance procedures, and effects in the final model included breed of sire-selection line combination, sire within breed-selection line, and location. Heritabilities were estimated by paternal half-sib analysis. Sires within breed-selection line represented a significant source of variation for all traits studied. Location had a significant effect on side diameter, side and britch diameter difference, and clean fleece weight. Age of ewe only affected clean fleece weight. Phenotypic and genetic correlations among side, britch, and core diameter measures were high and positive. Phenotypic correlations ranged from .68 to .75 and genetic correlations ranged from .74 to .89. The genetic correlations between side and britch diameter difference and side diameter or core diameter were small (-.16 and .28, respectively). However, there was a stronger genetic correlation between side and britch diameter difference and britch diameter (.55). Heritability of the difference between side and britch diameter was high (.46 +/- .16) and similar to heritability estimates reported for other wool traits. Results of this study indicate that relatively rapid genetic progress through selection for fiber diameter should be possible. In addition, increased uniformity in fiber diameter should be possible through selection for either side and britch diameter difference or side or britch CV.