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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Analysis of Carcass Traits of Steers Adjusted to Age, Weight, Or Fat Thickness Slaughter End Points

Authors
item Rios-Utrera, A. - UNIV. OF NEBR.-LINCOLN
item Cundiff, Larry
item Gregory, Keith - ARS COLLABORATOR
item Koch, Robert - RETIRED-UNIV. OF NEBR.
item Dikeman, Michael - KANSAS STATE UNIVERSITY
item Koohmaraie, Mohammad
item Van Vleck, Lloyd

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 2004
Publication Date: April 1, 2005
Citation: Rios-Utrera, A., Cundiff, L.V., Gregory, K.E., Koch, R.M., Dikeman, M.E., Koohmaraie, M., Van Vleck, L.D. 2005. Genetic analysis of carcass traits of steers adjusted to age, weight, or fat thickness slaughter end points. Journal of Animal Science 83:764-776.

Interpretive Summary: Carcass measurements from 1,664 steers from the GPU Project at USMARC were used to estimate heritabilities of, and genetic correlations among, 14 carcass traits adjusted to different end points (age, carcass weight, and fat thickness): hot carcass weight (HCW), dressing % (DP), adjusted fat thickness (AFT), longissimus muscle area (LMA), kidney-pelvic-heart fat % (KPH), marbling score (MS), yield grade (YG), predicted % of retail product (PRP), retail product weight (RPW), fat weight (FW), bone weight (BW), actual retail product % (RPP), fat % (FP), and bone %. The model included breed group, feed energy level, dam age, birth year, significant interactions, covariate for days on feed, and the appropriate covariate for end point nested within breed group (except age) as fixed effects, and additive genetic effect of animal and total maternal effect of dam as random effects. Parameters were estimated by REML. For some traits, estimates of heritability and phenotypic variance changed with different end points. Estimates of heritability for HCW, DP, MS, RPW, and BW at constant age, weight, or fat thickness, respectively, were 0.27, --, and 0.41; 0.19, 0.26, and 0.18; 0.40, 0.41, and 0.35; 0.42, 0.32, and 0.50; and 0.43, 0.32, and 0.48. Magnitude and/or sign of estimates of genetic correlation also changed across end points for 54 of the 91 trait pairs. Estimates for HCW-LMA, AFT-RPW, LMA-KPH, LMA-YG, LMA-PRP, LMA-FW, LMA-BW, LMA-RPP, LMA-FP, KPH-RPW, KPH-BW, and PRP-RPW at constant age, weight, or fat thickness, respectively, were 0.32, --, and 0.51; -0.26, -0.77, and --; -0.01, -0.10, and 0.25; -0.71, -0.89, and -0.66; 0.68, 0.85, and 0.63; -0.16, -0.51, and 0.22; 0.24, -0.19, and 0.30; 0.47, 0.57, and 0.27; -0.44, -0.43, and -0.18; -0.02, -0.48, and 0.15; -0.08, -0.55, and -0.04; and 0.26, 0.80, and -0.01. Fat thickness was highly correlated with YG (0.86 and 0.85 for common age and weight) and PRP (-0.85 and -0.82 for common age and weight), indicating that selection for reduced fat thickness would improve YG and PRP. Carcass quality, however, would be affected negatively because of moderate estimates of genetic correlation (0.34 and 0.35 for common age and weight) between MS and AFT. Estimates of heritability and phenotypic variance indicate that enough genetic variation exists to change measures of carcass merit by direct selection. For some carcass traits, however, magnitude of response would depend on effect of end point on heritability and phenotypic variance. Correlated responses to selection also would differ depending on end point. Heritability estimates indicate that if selection were practiced, response would be possible for the carcass traits evaluated. However, differences in estimates of phenotypic variances, heritabilities and genetic correlations for different end points suggest that direct and correlated responses to selection would be different for some traits depending on end point. At the same selection intensity, direct response to selection for retail product weight might be more effective at constant age or constant fat thickness than at constant weight. Regardless of end point, adjusted fat thickness was highly correlated genetically with yield grade and percent retail product, indicating that selection for reduced fat thickness would be effective for improving yield grade and increasing percent retail product. Carcass quality, however, would be affected negatively because of the positive and moderate estimates of genetic correlations for marbling score and adjusted fat thickness for all end points. Alternatively, selection for increased longissimus muscle area at constant age might improve yield grade and increase percent retail product without reducing marbling score.

Technical Abstract: Carcass measurements from 1,664 steers from the GPU Project at USMARC were used to estimate heritabilities of, and genetic correlations among, 14 carcass traits adjusted to different end points (age, carcass weight, and fat thickness): hot carcass weight (HCW), dressing % (DP), adjusted fat thickness (AFT), longissimus muscle area (LMA), kidney-pelvic-heart fat % (KPH), marbling score (MS), yield grade (YG), predicted % of retail product (PRP), retail product weight (RPW), fat weight (FW), bone weight (BW), actual retail product % (RPP), fat % (FP), and bone %. The model included breed group, feed energy level, dam age, birth year, significant interactions, covariate for days on feed, and the appropriate covariate for end point nested within breed group (except age) as fixed effects, and additive genetic effect of animal and total maternal effect of dam as random effects. Parameters were estimated by REML. For some traits, estimates of heritability and phenotypic variance changed with different end points. Estimates of heritability for HCW, DP, MS, RPW, and BW at constant age, weight, or fat thickness, respectively, were 0.27, --, and 0.41; 0.19, 0.26, and 0.18; 0.40, 0.41, and 0.35; 0.42, 0.32, and 0.50; and 0.43, 0.32, and 0.48. Magnitude and/or sign of estimates of genetic correlation also changed across end points for 54 of the 91 trait pairs. Estimates for HCW-LMA, AFT-RPW, LMA-KPH, LMA-YG, LMA-PRP, LMA-FW, LMA-BW, LMA-RPP, LMA-FP, KPH-RPW, KPH-BW, and PRP-RPW at constant age, weight, or fat thickness, respectively, were 0.32, --, and 0.51; -0.26, -0.77, and --; -0.01, -0.10, and 0.25; -0.71, -0.89, and -0.66; 0.68, 0.85, and 0.63; -0.16, -0.51, and 0.22; 0.24, -0.19, and 0.30; 0.47, 0.57, and 0.27; -0.44, -0.43, and -0.18; -0.02, -0.48, and 0.15; -0.08, -0.55, and -0.04; and 0.26, 0.80, and -0.01. Fat thickness was highly correlated with YG (0.86 and 0.85 for common age and weight) and PRP (-0.85 and -0.82 for common age and weight), indicating that selection for reduced fat thickness would improve YG and PRP. Carcass quality, however, would be affected negatively because of moderate estimates of genetic correlation (0.34 and 0.35 for common age and weight) between MS and AFT. Estimates of heritability and phenotypic variance indicate that enough genetic variation exists to change measures of carcass merit by direct selection. For some carcass traits, however, magnitude of response would depend on effect of end point on heritability and phenotypic variance. Correlated responses to selection also would differ depending on end point.

Last Modified: 10/1/2014
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