| Abstrakt: |
Data from 2,101 Brangus calves born from 1986 to 1990 were analyzed with a REML procedure using a derivative-free algorithm in a mixed linear animal model to obtain variance component estimates of ultrasound-measured longissimus muscle area and fat thickness. Direct additive heritabilities ( h2a) of .39 and .40 were obtained for age-constant weaning and yearling longissimus muscle area (WLMA and YLMA, respectively), with a genetic correlation (rg) of .66 between them. The rgof YLMA with birth weight (BWT), weaning weight (WWT), postweaning gain (PWG), yearling weight (YWT), frame score (FS), and scrotal circumference (SC) were .17, .29, .43, .38, .01, and .19, respectively. The h2aof age-constant yearling 12th rib fat thickness (FAT) was .14, and cattle averaged .44 cm (SD = .19). Positive rgwere obtained between FAT and WLMA (.19) and YLMA (.12). Negative rgof FAT with WWT, YWT, and SC were -.17, -.53, and -.33, respectively. Positive rgwere obtained between FAT and BWT (.52), PWG (.44), and FS (.14). Maternal heritabilities (h2m) of WLMA, YLMA, and FAT were .01, .01, and .10, respectively. Weight-constant WLMA, YLMA, and FAT h2awere .36, .39, and .11, respectively. Selection based on either age-constant YLMA or FAT could potentially result in 1.06 cm2or .005 cm change per year, respectively, which would be slightly greater than change from selection based on weight-constant YLMA or FAT. Selection based on WLMA or YLMA should be effective, and changes in these traits, growth, and SC should be possible in tandem. (ABSTRACT TRUNCATED AT 250 WORDS) |
