Author
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Snowder, Gary |
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Submitted to: Sheep and Goat Research Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/1/2002 Publication Date: 6/13/2002 Citation: Snowder, G.D. 2002. Composite trait selection for improving lamb production. Sheep and Goat Research Journal 17:42-49. Interpretive Summary: The objective of this review is to characterize the composite trait litter weight weaned and its components. The single most important economic trait in American commercial sheep production is the litter weight weaned per ewe exposed at breeding. This trait is of low heritability (on the order of 0.10) but selection response can be economically significant because of its shigh value per unit and large phenotypic variation. Litter weight weaned is a composite trait whose phenotypic expression is dependent upon several variables including ewe fertility, ewe prolificacy, embryo survival, lamb survival, lactation, maternal behavior, and lamb growth rate. Simultaneous improvements in all of these component traits have been observed when selecting for litter weight weaned. Such selection should result in appropriate emphasis on each component trait, resulting in a biologically balanced animal adapted to that environment. Selection solely for a component trait (litter size born, lamb weaning weight, etc.) is expected to result in significantly lower improvement in litter weight weaned compared to direct selection. Because of the economic importance of litter weight weaned producers are encouraged to consider it as a major selection trait. Alternatives to incorporate this trait into a selection program for purebred and commercial producers are discussed. Technical Abstract: The objective of this review is to characterize the composite trait litter weight weaned and its components. The single most important economic trait in American commercial sheep production is the litter weight weaned per ewe exposed at breeding. This trait is of low heritability (on the order of 0.10) but selection response can be economically significant because of its high value per unit and large phenotypic variation. Litter weight weaned is a composite trait whose phenotypic expression is dependent upon several variables including ewe fertility, ewe prolificacy, embryo survival, lamb survival, lactation, maternal behavior, and lamb growth rate. Simultaneous improvements in all of these component traits have been observed when selecting for litter weight weaned. Such selection should result in appropriate emphasis on each component trait, resulting in a biologically balanced animal adapted to that environment. Selection solely for a component trait (litter size born, lamb weaning weight, etc.) is expected to result in significantly lower improvement in litter weight weaned compared to direct selection. Because of the economic importance of litter weight weaned producers are encouraged to consider it as a major selection trait. Alternatives to incorporate this trait into a selection program for purebred and commercial producers are discussed. |
