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This Article Full Text (PDF) All Versions of this Article: jas.2008-1092v1 87/2/507    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kuehn, L. A. Articles by Notter, D. R. Search for Related Content PubMed PubMed Citation Articles by Kuehn, L. A. Articles by Notter, D. R.

Connectedness in Targhee and Suffolk flocks participating in the U.S. National Sheep Improvement Program

Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA 24061

larry.kuehn{at}ars.usda.gov

Abstract

Connectedness among animals in separate flocks reduces risk of biased comparisons when selecting across flocks on EBV. The objective in this study was to assess levels of connectedness in the genetic evaluation of weaning weight among Targhee and Suffolk flocks participating in the U.S. National Sheep Improvement Program (NSIP). Among flocks currently participating in NSIP, a total of 25,404 weaning weight and 35,794 pedigree records were available for 16 Targhee flocks, and 14,017 weaning weight and 18,311 pedigree records were available for 24 Suffolk flocks. Connectedness was measured using 2 different methods. First, numbers of progeny with recorded weaning weights from linking sires (defined as sires with progeny in multiple flocks or sires born in one flock with progeny in another flock) were counted. Second, connectedness was measured by calculating the average prediction error correlation of mean flock EBV (flock r_ij). Benchmarks for flock r_ij were established with 0.10 and 0.05 representing low and moderate risk of bias associated with comparing EBV among flocks, respectively. From 1995 through 2004, 44% of Targhee lambs with weaning weights were born to linking sires; in Suffolk lambs that value was 23%. Average flock r_ij were 0.10, 0.19, and 0.28 among Targhee flocks, and 0.02, 0.02, and 0.04 among Suffolk flocks, in 1990, 1995, and 2005, respectively, that participated in NSIP in all 3 yr. Among all active flocks in 2005, flock r_ij averaged 0.13 in Targhee and 0.03 in Suffolk. Hierarchical clustering of flocks based on flock r_ij revealed that all active Targhee flocks connect at a level near or above 0.10. In Suffolk flocks, 2 distinct clusters had formed in which connectedness was relatively high within each cluster (flock r_ij near 0.10) but near zero between clusters. Risk of bias in comparing EBV among flocks in Targhee is low; however, caution should be exercised when comparing EBV between Suffolk flocks from different clusters.

Key Words: connectedness • genetic evaluation • prediction error • sheep