Genetic Parameters for Carcass Traits and Stayability in Red Angus Cattle

In Red Angus cattle, the stayability (STAY) EPD predicts the probability of a female producing five consecutive calves by 6 years of age. A fundamental issue that arises with genetic prediction for STAY is animal’s accuracy values tend to improve later in life. An opportunity to overcome this is to use phenotypes recorded at younger ages to increase accuracy of STAY EPD earlier in an animal’s life. Therefore, the objective of this study was to estimate genetic relationships between STAY and HCW, ribeye area (REA), back fat (BF), and marbling score (MARB), as well as, their indicator traits, ultrasound ribeye area (UREA), ultrasound back fat (UBF), and ultrasound intramuscular fat percentage (UIMF). Data for the analyses were obtained from the Red Angus Association of America. Following data editing procedures, 1,676, 1,717, 1,459, 1,721, 29,406, 29,477, 29,269, and 43,328 phenotypic records were used for the analysis of REA, BF, MARB, HCW, UREA, UBF, UIMF, and STAY, respectively. (Co)Variance between traits were estimated using multiple two-trait animal models and the software package ASReml. These parameters were then used to calculate heritability and genetic correlations between each of the two trait pairs. The fixed effect of contemporary group was included for all traits. For all carcass and ultrasound traits, fixed effects also included sex (bull, heifer, and steer), and the linear covariate of age of measurement. A random effect of animal was included in each analysis to estimate additive genetic effects. Heritability estimates were 0.26 0.08, 0.24 0.07, 0.30 0.08, 0.26 0.07, 0.38 0.02, 0.40 0.02, 0.39 0.02, and 0.10 for REA, BF, MARB, HCW, UREA, UBF, UIMF, and STAY (averaged across all analyses), respectively. Results of the analysis indicated that genetic relationships were strongest in magnitude between STAY and BF (0.53 0.20), MARB (0.40 0.20), UBF (0.37 0.07), and UREA (0.19 0.07). Whereas, genetic correlations between STAY, and REA (0.01 0.21), HCW (0.14 0.21), and UIMF (-0.01 0.07) suggested minimal, if not zero, relationship between the traits. Results show favorable genetic relationships are present between the carcass traits MARB and UREA and STAY and unfavorable relationships are estimated between BF, UBF and STAY. In addition, the trait UBF could be introduced into a multiple trait model to improve accuracy of STAY genetic predictions due to the magnitude of the correlation and availability of data.