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Genetic evaluation of Angus cattle for carcass marbling using ultrasound and genomic indicators

M. D. MacNeil^*, J. D. Nkrumah, B.W. Woodward and S. L. Northcutt

^* USDA, Agricultural Research Service, Miles City, MT 59301 , Merial Limited, Duluth, GA 30096 American Angus Association, Saint Joseph, MO 64506

mike.macneil{at}ars.usda.gov

Abstract

Objectives were to estimate genetic parameters needed to elucidate the relationships of a molecular breeding value for marbling (MBV), intramuscular fat of yearling bulls measured with ultrasound (IMF) and marbling score of harvested steers (MRB), and to assess the utility of MBV and IMF in prediction of breeding value for MRB. Records for MRB (n = 38,296) and IMF (n = 6,594) were from the American Angus Association data base used for national cattle evaluation. There were 1006 records of MBV used in this study. (Co)variance components were estimated with ASREML fitting an animal model with fixed contemporary groups for MRB and IMF similar to those used in the Angus national genetic evaluation. The overall mean was the only fixed effect included in the model for MBV. Heritability estimates for carcass measures were 0.48±0.03, 0.31±0.03, and 0.98±0.05 for MRB, IMF, and MBV, respectively. Genetic correlations of IMF and MBV with MRB were 0.56±0.09 and 0.38±0.10, respectively. The genetic correlation between IMF and MBV was 0.80±0.22. These results indicate the MBV evaluated may yield approximately 20% greater genetic advance when used as an indicator trait for genetic prediction of MRB than IMF. However, neither of these indicators alone provides sufficient information to produce highly accurate prediction of breeding value for the economically relevant trait MRB. Given the goal of highly accurate prediction of true breeding value for MRB, results of this work point to the need to continue 1) progeny testing and 2) increasing the genetic correlation between the MBV and MRB.

Key Words: Beef cattle • Marbling • Genetic Parameters • Molecular breeding value • Ultrasound