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Reproductive performance of dorset ewes in the star accelerated lambing system

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dc.contributor.authorLewis, Ronald M.en
dc.contributor.committeechairNotter, David R.en
dc.contributor.committeememberPearson, Ronalden
dc.contributor.committeememberUmberger, Steven H.en
dc.contributor.committeememberVinson, William E.en
dc.contributor.committeememberHinkelmann, Klausen
dc.contributor.committeememberHoeschele, Inaen
dc.contributor.committeememberHohenboken, William D.en
dc.contributor.departmentAnimal Scienceen
dc.date.accessioned2014-03-14T21:18:15Zen
dc.date.adate2008-08-25en
dc.date.available2014-03-14T21:18:15Zen
dc.date.issued1990-05-05en
dc.date.rdate2008-08-25en
dc.date.sdate2008-08-25en
dc.description.abstractReproductive performance of Dorset ewes in the Cornell University STAR accelerated lambing program was evaluated. This program consists of five 30-d concurrent breeding and lambing periods per year beginning on January 1 (Sl), March 15 (S2), May 27 (S3), August 8 (S4) and October 20 (S5). Optimally, a ewe could lamb every 7.2 mo beginning at 1 yr of age, Records on 1,084 ewes over 7 yr beginning S1, 1982 Reproductive traits considered were ewe fertility, prolificacy, days to first lambing (DFL) and days between lambing (DBL). Fertility and prolificacy differed (P < .001) by exposure seasons. Exposure during favorable seasons (S1, S4, S5) increased fertility (P < .001) and prolificacy (P < .01) over that observed in unfavorable seasons (S2, S3). On average, first lambing occurred at 476 ± 5 d with ewe lambs first exposed during S1, S4 and S5 lambing at younger ages (P < .001). Ewes had more DBL (P < .001) if initial exposure following lambing occurred during an unfavorable season. A curvilinear relationship of ewe age with fertility (P < .001) , prolificacy (P < .01) and DBL (P < .05) was observed in ewes less than 4 yr old. At first exposure following lambing, fertility was lower (P < .001) than at subsequent exposures and ewes that had nursed lambs were less prolific (P < .01) than those that had not. Prolificacy and nursing status had little effect on fertility or DBL (P > .10). Fertility was transformed to an underlying liability scale based on the expected fertility of ewes of a given age and reproductive history. Variance components were estimated by least-squares (LS) and restricted maximum likelihood (REML) procedures. First-exposure fertility was not heritable. heritabilities for fertility at first post-lambing exposure, first-lambing prolificacy, and second-lambing prolificacy were .191 ± .088 (LS) and .200 ± .132 (REML), .914 ± .091 (LS) and .158 ± .144 (REML), and .168 ± .082 (LS) and .210 ± .137 (REML), respectively. Genetic variation in DFL (P < .01) and DBL (P < .001) was found. Although intrasire ewe variation was detected for prolificacy (P < .001) and DBL (P < .01), repeatability estimates were low and smaller than heritability.en
dc.description.degreePh. D.en
dc.format.extentxiv, 137 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-08252008-162636en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-08252008-162636/en
dc.identifier.urihttp://hdl.handle.net/10919/39247en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V856_1990.L482.pdfen
dc.relation.isformatofOCLC# 21709029en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subject.lccLD5655.V856 1990.L482en
dc.subject.lcshSheep -- Reproductionen
dc.titleReproductive performance of dorset ewes in the star accelerated lambing systemen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineAnimal Scienceen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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