Evaluation of sire differences in postweaning growth traits and carcass characteristics, and the use of ultrasound measurements as predictors of observed carcass values in purebreed beefmaster steers

Abstract

Postweaning growth, carcass yield, and lean quality traits of 56 purebred Beefinaster steers, representing I I purebred Beefinaster sires were used in a cooperative study sponsored by Beefmaster Breeders United. The steers were grazed on wheat pasture for 69 days, then finished in drylot at the Texas A&M Agricultural Research Center, McGregor, TX. Using real-time ultrasound measures of fat thickness and live weight, the steers were sorted into 3 kill groups: 112, 140, and 168-d. A fixed effects model was used with sire and kill group as independent variables to analyze initial weight (IW), grass ADG (GADG), feedlot ADG (FADG), final weight (FW), carcass weight (CW), fat thickness (FT), kidney, pelvic, and heart fat (KPH), ribeye area (REA), yield grade (YG), marbling score (MS), quality grade (QG), and shear values in previously published research for IW (269 ︢4 kg), GADG (0.71 .︢03 kg), FADG (1.58 .︢02 kg), and FW (534 ︢5 kg). The steers met industry-acceptable ranges for CW (3 3 5 ︢3 kg), FT (I. 10 ︢.05 cm), KPH (I. 91 + .09 %), REA (80.2 ︢1.2 cm2), YG (2.98 .︢08), and QG (672 ︢5). The steers were clearly acceptable in Wamer-Bratzler tenderness, with a mean shear force of 2.74 .︢07 k-a 0. Kill group effect was significant for IW (P <.05), GADG (P <.001), FADG (P < .001), FW (P <.Ol), CW (P <,05), FT (P <.05), and SF (P <.05). There was no kill group effect for KPH, REA, YG, MS, or QG. Sire differences were observed in IW (P < .05) and GADG (P <.001). Sire effects were not found for FADG, FW, CW, FT, KPH, REA, YG, MS, QG, or SF. The correlation between ultrasound fat thickness and observed carcass fat thickness was 0.69. The correlation between ultrasound ribeye area and observed carcass ribeye area was 0.59.