Zilpaterol improves feeding performance and fabrication yield of concentrate-finished cull cows.

The objective of this study was to quantify the effects of zilpaterol hydrochloride (ZH) on feeding performance and fabrication yield of concentrate-finished cull cows. Three hundred twenty commercial cull cows (2 to 10 yr old) were obtained from ranches in Missouri and South Dakota and assigned to 1 of 2 treatments: 1) a control diet containing no ZH and 2) a diet that contained ZH. Cows were fed for 75, 88, or 110 d, and all received the control ration until ZH treatments were initiated. Twenty-four days before slaughter, ZH feeding began for the designated treatment pens; cows were fed ZH [8.33 mg/kg (100% DM basis)] for 20 d with a 4-d withdrawal period before slaughter. No differences (P>0.05) were detected between the 2 treatment groups for initial BW or DMI. Final BW (640.5 vs. 619.1 kg), ADG for the last 24 d (2.75 vs. 2.17 kg), and G:F for the last 24 d (0.160 vs. 0.126) were greater (P<0.01) in cows fed ZH than the control cows. No differences (P > 0.05) were found for lean or skeletal maturity score, fat thickness, LM area, HCW, or calculated yield grade among the 2 treatment groups. Feeding ZH increased (P<0.01) HCW (390.1 vs. 369.2 kg), dressed carcass yield (61.01 vs. 59.45%), and LM area (93.3 vs. 86.5 cm(2)) and decreased (P<0.01) marbling score (Slight(63) vs. Slight(86)) compared with control cows. Cows fed ZH had greater (P<0.05) primal weights for chuck (mock) tender (2.63 vs. 2.28 kg), lip-on rib eye roll (13.54 vs. 12.56 kg), top sirloin butt (12.74 vs. 11.82 kg), top (inside) round (14.58 vs. 12.89 kg), and peeled knuckle (12.87 vs. 11.51 kg) while yielding a decreased percentage of mechanical knife trimmings (1.15 vs. 1.35%; P<0.01) and more top (inside) rounds (3.71 vs. 3.46%; P=0.02) than the control cows. No differences (P>0.07) were found for the remaining fabrication yield attributes. The ZH-treated cows had greater (P<0.05) fabrication dollar values for chuck (mock) tender (8.82 vs. 7.66 $/carcass), lip-on rib eye roll (64.20 vs. 59.56 $/carcass), strip loin (0 × 1; 49.13 vs. 44.75 $/carcass), top sirloin butt (35.60 vs. 33.01 $/carcass), bottom round (flat; 44.23 vs. 39.23 $/carcass), top (inside) round (60.30 vs. 53.33 $/carcass), knuckle (peeled; 44.26 vs. 39.57 $/carcass), and total salable yield (879.50 vs. 803.70 $/carcass) than control cows. These results suggest the feeding of ZH to concentrate-finished cull cows enhances production efficiencies and can add new value to the cull cow market.