Use of Ultrasound to Identify Brangus Cattle with Superior Intramuscular Fat and Other Carcass Traits

Abstract

The objectives of this research were 1) to determine the effects of sire on the expression of intramuscular fat and 2) to determine the relationship of intramuscular fat with selected performance traits. Purebred Brangus cattle (n = 1,215) were subjected to real-time ultrasound evaluation of body composition; traits recorded were the 12th-13th rib subcutaneous fat thickness (FT), longissimus area (LA), and percentage intramuscular fat (IMF). Performance data provided by the International Brangus Breeder’s Association (IBBA) included birth BW (BBW; n = 323), weaning BW (WBW; n = 328), yearling BW (YBW; n = 1,087), and scrotal circumference (SC; n = 329). Data were analyzed to determine genetic relationships with the animal model using multiple trait restricted maximum likelihood (MTDFREML) procedures. Contemporary group was included in the model as a fixed effect, and age (in days) was included as a covariate. Analyses of covariant models were examined to determine the relative importance of sire and carcass traits to IMF. Genetic correlations of IMF with LA, FT, and YBW were –0.25, 0.36, and 0.31, respectively. Sire, FT, and LA were significant (P<0.05) sources of variation in IMF; whereas BBW, WBW, YBW, SC, and age did not significantly influence IMF. These results suggest that IMF estimated by real-time ultrasound is moderately heritable. Because IMF is an important factor in determining quality grade (QG), ultrasonically determined IMF may be considered in selecting seedstock for increased QG.