Repeatability of Conception Rate and Litter Size for Ewes in an Accelerated Lambing System

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Abstract
Repeatabilities (t) for conception rate and litter size were estimated from data on 131 Finnish Landrace crossbred ewes lambing between 1974 and 1978. Ewes were in an accelerated lambing system and were allowed to lamb three times every 2 years in September, January and April. A total of 955 exposures, resulting in 717 lambings, was recorded. When data from all lambing seasons were analyzed together, overall ewe effects on conception rate were significant. Repeatability estimates varied with the specific analytical model and ranged from .076 ± .022 to .127 ± .024. The ewe ✕ season interaction was not significant for conception rate; the interaction variance component was close to zero. Within-season repeatabilities for conception rate were not significant for lambings in January ( t = .056 ± .062) or April (t = .009 ± .079) but were significant for September lambings (t = .188 ± .046). The use of conception rate for September lambing as a culling criterion would have maximized the performance of the remaining selected ewes in all seasons. Overall ewe effects on litter size were significant; repeatability estimates were .166 ± .031 and .156 ± .032. Within-season repeatabilities for litter size were .162 ± .066 in January, .375 ± .080 in April and .318 ± .072 in September. The ewe ✕ season interaction was significant for litter size. Correlations between ewe effects in different seasons were .683 ± .508 for January and April, .427 ± .460 for January and September and .301 ± .327 for April and September. Direct selection for litter size within each season would have nearly maximized the performance of remaining ewes, although indirect selection based on April litter size would have resulted in a slightly greater response than direct selection for January litter size. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science

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