|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2000
Publication Date: 2/1/2000
Citation: Bromley, C.M., Van Vleck, L.D., Snowder, G.D. 2000. Genetic correlations for litter weight weaned with growth, prolificacy, and wool traits in Columbia, Polypay, Rambouillet and Targhee sheep. Journal of Animal Science 79:339-346. Interpretive Summary: Economic traits of sheep include litter size, weights at various ages, and fleece traits such as weight, grade, and staple length. A measure of ewe productivity for lamb production is litter weight weaned which is a composite trait of litter size at weaning and weaning weight. This composite trait is easily measured and might be suitable for selection for ewe productivity. This study of Columbia, Polypay, Rambouillet, and Targhe sheep showed that litter weight weaned generally was lowly heritable (about the same as litter size) but that enough genetic variation existed for selection. Averaged over all breeds, the genetic correlations between litter weight weaned and litter size at birth were small and positive and were large and positive with litter size weaned. Similarly, the genetic correlations with birth weight were small and positive and with gain from birth to weaning were moderately large and positive. The genetic correlations with the fleece traits averaged near zero. These results, although with possible variation from breed to breed, suggest that no adverse genetic responses in other economic traits would result from selection for litter weight at weaning.
Technical Abstract: Total litter weight weaned at 120 d per ewe lambing can be used as a measure of ewe productivity. Genetic correlations for Columbia, Polypay, Rambouillet and Targhee sheep were estimated using REML with animal models between litter weight weaned and fertility, growth and wool traits. Total number of observations ranged from 4,609 to 6,469 for litter weight weaned, from 5,140 to 7,095 for fertility traits, from 7,750 to 9,530 for growth traits, and from 4,063 to 34,746 for wool traits across the four breeds. For litter weight weaned, heritability estimates were low and ranged from .03 to .12. Relative variances due to permanent environmental effects and effects of mating sire were small. Estimates of direct genetic correlations with litter weight weaned generally varied from breed to breed. The ranges were as follows: -.30 to .43 with fertility traits, -.03 to .98 for growth traits and -.20 to .67 with wool traits. Results suggest that correlated responses for fertility, growth and wool traits if selection is practiced on litter weight weaned might vary from breed to breed.