|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/1999
Publication Date: 2/1/2000
Citation: Bromley, C.M., Snowder, G.D., Van Vleck, L.D. 2000. Genetic parameters among weight, prolificacy and wool traits in Columbia, Polypay, Rambouillet and Targhee sheep. Journal of Animal Science 78:846-858.
Interpretive Summary: Genetic correlations among traits as well as direct and maternal heritabilities are needed to develop multiple trait genetic evaluation programs and to combine with economic values of the traits to design selection indexes for optimizing economic returns from selection. This study of four breeds of sheep (Columbia, Polypay, Rambouillet, and Targhee) )of three weight, three prolificacy, and three wool traits involved thousands of analyses to estimate these parameters from probably the largest analysis of sheep data ever done. The estimates were variable from breed to breed even though the numbers of records per breed were in the thousands or tens of thousands. Nevertheless, patterns emerged which suggest which traits need to be included in genetic evaluations as well as likely relationships among traits. For example, there were no important positive or negative correlations between wool traits and either weight or prolificacy traits. Maternal genetic effects were important only for birth and weaning weights. Weight traits were positively correlated with fleece weight and staple length but showed little correlation with fleece grade. Prolificacy traits were positively correlated with weight traits. These correlations also can be used to predict response in any trait if selection is on one or a combination of traits.
Technical Abstract: Genetic parameters for Columbia, Polypay, Rambouillet and Targhee sheep were established using REML with animal models for prolificacy, weight and wool traits. All bivariate analyses included a covariance between additive genetic effects of two traits plus appropriate additional covariances. Number of observations by breed ranged from 5,140 to 7,095 for prolificacy traits, from 7,750 to 9,530 for weight traits, and from 4,063 to 34,746 fo wool traits. Heritability estimates ranged from .03 to .11 for prolificacy traits (litter size at birth and litter size at weaning), from .09 to .26 for weight traits (birth weight and average daily gain), and from .25 to .53 for wool traits (fleece weight, fleece grade and staple length). Estimates of direct genetic correlations among prolificacy and weight traits were positive and ranged from .58 to 1.00 and .18 to 1.00 respect- ively. Estimates of direct genetic correlation between fleece weight and staple length were positive (.50 to .70), but were negative (but favorable between fleece weight and fleece grade (-.60 to -.34) and between staple length and fleece grade (-.72 and -.40). Prolificacy and wool traits were essentially uncorrelated. Weight and prolificacy traits were slightly positively correlated. Weight traits had a moderate positive direct genetic correlation with fleece weight and staple length, but were uncorrelated with fleece grade. These estimates of genetic parameters between prolificacy, weight, wool traits can be used to construct multiple trait selection indexes for dual-purpose sheep.