J. Anim Sci.
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J. Anim Sci. 1970. 30:1-5.
© 1970 American Society of Animal Science
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Repeatability and Heritability of Components of Reproductive Efficiency in Fine-Wool Sheep

Maurice Shelton and James W. Menzies1

Texas A&M University, Agricultural Research Center, McGregor and Texas Agricultural Experiment Station, Sonora

Abstract

Repeatability and heritability estimates were obtained for three separate entities contributing to total reproductive efficiency in two flocks of fine-wool sheep. The three factors studied were fertility (parous vs. nonparous), prolificacy (single vs. multiple birth for a given parturition) and livability (dead vs. alive at weaning). Each of these traits was classified on an all or none basis and analysed appropriately. A total of 6,483 matings and 6,297 offspring were involved in two flocks. Prolificacy had the highest repeatability (13.20% as an average for the two flocks); whereas, fertility was low (4.4%) with an actual negative value in one flock in which the ewes were on a suboptimum nutritional level. The repeatability of lamb survival was intermediate in both flocks with an average value of 8.27%. Heritability estimates were obtained by paternal half-sib analyses. The highest heritability value was obtained for fertility in the flock in which the ewes were subjected to a suboptimal nutritional level throughout much of their productive life (26.8%). By contrast, the lowest estimate (6.7%) was obtained for the same trait in a second flock where nutritional level was more than adequate for proper development of the ewe. The second highest heritability estimate was for livability (19.0%) of the lambs in a flock in which little artificial rearing of lambs was practiced. The heritability of prolificacy was intermediate among the three traits in each flock. However, it is suggested that this is the trait deserving greater attention in selection programs.

Footnotes

1 Professor and Assistant Animal Husbandman, Texas A&M University, Texas Agricultural Experiment Station, McGregor and Sonora, respectively.






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