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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #161197
Title: ESTIMATES OF GENETIC PARAMETERS AND GENETIC CHANGE FOR REPRODUCTION, WEIGHT, AND WOOL CHARACTERISTICS OF RAMBOUILLET SHEEP

Author
item Hanford, Kathryn
item Van Vleck, Lloyd
item Snowder, Gary

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2004
Publication Date: 3/1/2005
Citation: Hanford, K.J., Van Vleck, L.D., Snowder, G.D. 2005. Estimates of genetic parameters and genetic change for reproduction, weight, and wool characteristics of rambouillet sheep. Small Ruminant Research 57:175-186.

Interpretive Summary: Few long-term selection studies have been conducted with dual-purpose Western range sheep in the United States. Analyses of Columbia and Targhee sheep selected concurrently with the Rambouillet sheep summarized in this paper indicated that both Columbia and Targhee sheep responded favorably to selection for weaning performance. The objective of this study was to document genetic trends in production traits of the Rambouillet breed at the United States Sheep Experiment Station (USSES), Dubois, ID, over a 49-yr period (1950-1998), where selection has been based on weaning performance under range conditions. The traits analyzed included prolificacy, weight, and wool traits. Another objective was to compare estimates of genetic change for each trait from single-trait analyses or from a seven-trait analysis. Records were for Rambouillet sheep from data collected from 1950 to 1998 at the U.S. Sheep Experiment Station, Dubois, ID. Number of observations were 44,211 for litter size at birth and litter size at weaning, 35,604 for birth weight, 34,114 for weaning weight, 39,820 for fleece weight, 39,821 for fleece grade, and 3,574 for staple length. Genetic parameters from both single-trait and two-trait analyses for these prolificacy, weight, and wool traits were estimated using REML with animal models. Results of this study agree with results of the previous studies of the Columbia and Targhee breeds. Selection based on weaning performance over a long period resulted in moderate positive responses for both litter size at weaning and weaning weight in the Rambouillet, Targhee and Columbia flocks. Although litter size at birth and weaning are lowly heritable, positive genetic correlations between both of these traits and weaning weight and litter size at weaning, which are components of weaning performance, suggest that selection for weaning performance would result in positive genetic gains in both litter size at birth and birth weight. Although most of the genetic correlations between wool traits and weaning performance were in an undesirable direction, the correlations were also low so that the unfavorable correlated responses in the wool traits would not be great. The economic value of selection response for increased weaning performance would offset correlated decreases in value of wool traits under today's market prices.

Technical Abstract: Genetic parameters from both single-trait and two-trait analyses for prolificacy, weight, and wool traits were estimated using REML with animal models for Rambouillet sheep from data collected from 1950 to 1998 at the U.S. Sheep Experiment Station, Dubois, ID. Number of observations were 44,211 for litter size at birth and litter size at weaning, 35,604 for birth weight, 34,114 for weaning weight, 39,820 for fleece weight, 39,821 for fleece grade, and 3,574 for staple length. Direct heritability estimates from single-trait analyses were 0.09 for litter size at birth, 0.06 for litter size at weaning, 0.27 for birth weight, 0.20 for weaning weight, 0.51 for fleece weight, 0.16 for fleece grade, and 0.58 for staple length. Estimate of direct genetic correlation between litter sizes at birth and weaning was 0.76 and between birth and weaning weights was 0.60. Estimate of genetic correlation between fleece weight and staple length was positive (0.45), but negative between fleece weight and fleece grade (-0.47) and between staple length and fleece grade (0.52). Estimates of genetic correlations were near zero between birth weight and litter size at weaning, small and positive between birth weight and litter size at birth, and moderate and positive between weaning weight and litter size traits. Fleece weight, fleece grade, and staple length were slightly but negatively correlated with both litter size traits. Estimates of correlations between weight traits and fleece weight were positive and low to moderate. Estimates of correlations between weight traits and fleece grade were negative and small, while estimates between weight traits and staple length were positive and small. Estimates of breeding values averaged by year of birth from single-trait analyses and from seven-trait analyses using parameters estimated from two-trait analyses were compared as measures of genetic change. Estimated breeding values averaged by year of birth from both the single-trait and seven-trait analyses for the prolificacy and weight traits increased over time, while those for fleece weight decreased and those for the other wool traits were unchanged. Estimated changes in breeding values over time did not differ substantially for the single-trait and seven-trait analyses, except for traits highly correlated with another trait that was responding to selection.