Lamb Production and Its Components in Pure Breeds and Composite Lines. III. Genetic Parameters

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Abstract
Estimates of repeatability, heritability and phenotypic and genetic correlations were obtained for various maternal measures of lamb production and their component traits: fertility, litter size, neonatal and preweaning survival and weaning weight. The data comprised 10,959 ewe breeding season records at four seasons over 4 yr on 4,219 ewes that were the progeny of 412 sires in five breeds and two ½ Finnsheep composite stocks. Intraclass correlation estimates of repeatability were .05 to .06 (± .01) for number and weight of lamb weaned per ewe exposed and ranged from .06 to .15 (± .02) for the various components. Regression estimates of repeatability were higher than the intraclass correlation estimates for most traits. Half-sib heritability estimates for single ewe records were .03 ± .02 for number and .06 ± .02 for weight of lamb weaned per ewe exposed, .06 ± .02 for fertility, .11 ± .04 for litter size, .02 ± .04 for neonatal survival, .07 ± .04 for preweaning survival and .10 ± .05 for lamb weaning weights. Corresponding estimates for lifetime performance were: .06 ± .05, .15 ± .05, .09 ± .05, .16 ± .06, .10 ± .05, .15 ± .06 and .13 ± .07, respectively. Heritability estimates of most traits increased with parity. Regressions of daughter on dam mean performance agreed with half-sib heritabilities for litter size and weaning weight, but were smaller for fertility, lamb survival and number and weight of lambs weaned per ewe exposed. Phenotypic and genetic correlations among all traits indicated that all component traits contributed to phenotypic variation in number and weight of lamb weaned per ewe exposed, but that lamb survival and weaning weight were more important than fertility and litter size in predicting breeding values for ewe productivity under the semi-intensive accelerated lambing management. Copyright © 1985. American Society of Animal Science . Copyright 1985 by American Society of Animal Science

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