Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2009
Publication Date: 4/1/2010
Publication URL: http://www3.interscience.wiley.com/cgi-bin/fulltext/122651481/HTMLSTART
Citation: Mousel, M.R., White, S.N., Hoesing, L.M. 2010. Association analysis of a CCR5 variant with ewe lifetime production in 3 breeds of sheep. Animal Genetics. 41(2):222-223. Interpretive Summary: In sheep, modification in a gene, called CCR5, is associated with reduced concentration of ovine progressive pneumonia virus (OPPV) DNA. Increased OPPV DNA concentration was associated with increased signs of ovine progressive pneumonia (OPP). Thus, sheep with the genetic modification may be less likely to develop clinical signs of OPP, and a genetic test for the modification may enable producers to reduce the incidence of OPP. However, before a genetic test can be used, we must determine whether the genetic modification affects ewe lifetime production. A total of 370 Rambouillet, Polypay and Columbia ewes were tested for the CCR5 modification. Their lifetime production records for total number of lambs born, total number of lambs raised to weaning, total kilograms of lamb weaned and age, in years, at last lambing were evaluated to determine if CCR5 had an effect on these production traits. No statistically significant association was found between the production traits and the CCR5 modification. Thus, using the CCR5 modification in a genetic test to reduce concentrations of OPPV DNA should not result in reduced production in the traits we evaluated.
Technical Abstract: A deletion in the promoter region of CCR5 associates with a 50% reduction in proviral concentration (log10 env copies/microgram DNA) of ovine progressive pneumonia virus (OPPV) in blood. Nearly half of all flocks in the U.S. have at least one sheep infected with OPPV. Because OPP provirus concentrations in blood correlate with the degree of histological lesions in affected tissues, use of the CCR5 promoter variant in marker-assisted selection might reduce pathology; however it must be determined whether such selection positively or negatively associates with production traits. We determined whether the three CCR5 promoter insertion/deletion genotypes and four ewe lifetime production traits were associated. Peripheral blood leukocyte DNA and lifetime records from 130 Rambouillet, 126 Polypay, and 114 Columbia ewes were used. Production traits on a per ewe basis were evaluated and included: total adjusted 120-d weaning weight of all lambs born (120d kg), total lifetime number of lambs born (TB), total count of lambs raised to weaning (TR), and age of ewe, in years, at last lambing before being culled (AGE). A Taqman assay (Applied Biosystems, Foster City, CA) was used to genotype the CCR5 promoter insertion/deletion. For association analysis, mixed procedure of SAS 9.1 (SAS Institute, Cary, NC) was used. The model included breed, CCR5 promoter insertion/deletion genotype, year ewe was born, and age at last lambing as fixed effects, sire as a random effect, and log10 of OPP provirus concentration as a covariate. Breed and age at last lambing were significantly associated with TB (P<0.01), TR (P<0.01), and 120d kg (P<0.01). None of the three CCR5 promoter insertion/deletion genotypes had significant positive or negative associations with any of the ewe lifetime production traits (all P>0.59). Thus, using the CCR5 promoter deletion in marker-assisted selection to reduce concentrations of OPPV should not result in deleterious correlated responses with the economically important production traits that we evaluated.