76 Camera vision grading and objective tenderness outcomes of steers fed lubabegron fumarate for the final 56 d of the feeding period

Limited research has compared no beta-agonist, ractopamine and lubabegron in feedlot cattle. We evaluated carcass quality and yield variables using a camera grading instrument and also examined objective tenderness outcomes. Treatments were negative control (no beta-ligand; CON), Optaflexx (ractopamine hydrochloride, 300 mg·steer-1·d-1 for 35 d; OPT), and Experior (lubabegron fumarate, 36 mg·steer-1·d-1 for 56 d + 4 d removal; 0EXP) fed for 198 d. Additional EXP treatments investigated total days on feed (DOF) of 184 d (-14EXP), 212 d (+14EXP) and 226 d (+28EXP). Carcasses (n = 2,517) were instrument graded 24 h post-mortem. Longissimus tenderness and lipid content were evaluated in a subset (n = 361) of carcasses via slice shear force and ether extract. Statistical analyses were conducted using mixed models; pen was the experimental unit, treatment was the fixed effect, block was a random effect, and means were separated with the Tukey-Kramer adjustment. Longissimus muscle area (LMA) was 4.0 to 6.2 cm2 larger (P < 0.01) for steers fed EXP compared with CON, which did not differ from OPT. Weight corrected LMA (LMA:HCW) was 1.3 cm2/100 kg larger (P < 0.01) for -14EXP compared with CON. Marbling score was 31 to 39 points lower (P < 0.01) for -14EXP compared with CON and OPT, whereas 0EXP, +14EXP and +28EXP were similar to CON and OPT. Total number of fat pieces within the longissimus did not differ (P = 0.11) across treatments, however number of fat pieces in the lateral one-half of the longissimus decreased (P ≤ 0.03) for -14EXP and +28EXP, whereas +14EXP tended (P = 0.09) to decrease compared with CON. Total meat area was 3.7 percentage points greater (P < 0.01) for -14EXP compared with CON; +14EXP and +28EXP tended (P = 0.07) to be greater than CON. Total fat area was 1.6 to 1.8 percentage points less (P ≤ 0.02) for 0EXP, +14EXP, and +28EXP when compared with CON. Compared with CON, dorsal-ventral longissimus distance increased (P < 0.01) by 3.3 to 5.4% for -14EXP, 0EXP, +14EXP and +28EXP. Medial-lateral longissimus distance increased 1.9 to 2.5 % (P < 0.01) for +14EXP and +28EXP compared with CON, whereas -14EXP tended (P = 0.08) to increase. Percentage intramuscular fat (IMF) was similar (P ≥ 0.44) for +14EXP, +28EXP, and OPT compared with CON, whereas 0EXP tended (P = 0.09) to be less. Marbling score and IMF were moderately correlated (r = 0.66). Slice shear force values were 20.1% greater (P < 0.02) for +14EXP compared with CON, whereas 0EXP tended (P = 0.09) to be greater and +28EXP, -14EXP and OPT were similar (P ≥ 0.28) to CON. These findings illustrate the effect of EXP on carcass traits and tenderness in feedlot cattle.