The effects of technology use in feedlot production systems on feedlot performance and carcass characteristics

The objectives of this study were to examine the effects of feedlot production systems with and without the use of a β-adrenergic agonist compared to an all-natural production program on feedlot performance and carcass characteristics. Crossbred beef steers (n = 336; initial BW = 379 ± 8 kg) were randomized to 1 of 3 treatments in a randomized complete block design (RCBD; 14 steers/pen; 8 pens/treatment). Treatments consisted of an all-natural treatment (NAT), a conventional treatment (CONV), and a conventional treatment with a β-agonist (CONV-Z). All treatments were fed the same basal diet with NAT cattle receiving no growth promoting technologies. The CONV and CONV-Z cattle were implanted with 40 mg of estradiol and 200 mg of trenbolone acetate (TBA) on d 0 and were fed 33 and 9 mg/kg of monensin and tylosin daily, respectively. The CONV-Z cattle were fed zilpaterol hydrochloride (ZH) at 6.76 mg/kg (90% DM basis) for the last 20 days on feed (DOF) There was no effect of treatment on DMI (P = 0.83); however, CONV-Z steers gained 3.8% faster (1.64 vs. 1.58 kg/d; P \u3c 0.01) and were 5.3% more efficient (0.160 vs. 0.152; P \u3c 0.01) than CONV steers, and CONV steers gained 32.8% faster (1.58 vs. 1.19 kg/d; P \u3c 0.01) and were 26.7% more efficient (0.152 vs. 0.120; P \u3c 0.01) than NAT steers. There was a 35.7% improvement in estimated carcass gain (1.29 vs. 0.95 kg/d; P \u3c 0.01) and a 32.6% improvement in carcass efficiency (0.126 vs. 0.095; P \u3c 0.01) for CONV-Z steers compared to NAT steers. Hot carcass weight was increased by 8 kg for CONV-Z steers compared to CONV steers (394 vs. 386 kg; P = 0.05) and 46 kg compared to NAT steers (394 vs. 348 kg; P \u3c 0.01). Longissimus muscle area was increased by 3.6 cm2 for CONV-Z steers compared to CONV steers (92.29 vs. 88.67 cm2; P = 0.02) and 12.1 cm2 for CONV-Z steers compared to NAT steers (92.29 vs. 80.16 cm2; P \u3c 0.01), resulting in a 9.6% unit increase in USDA yield grade (YG) 1 (15.14 vs. 5.52%; P \u3c 0.05) and a 21.6% unit reduction in USDA YG 3 for CONV-Z steers compared to CONV steers (30.70 vs. 52.32%; P \u3c 0.05). The CONV-Z steers had a lower marbling score compared to the other treatments (432; P \u3c 0.01), resulting in an 11.7% unit increase (20.70 vs. 9.03%; P \u3c 0.05) in USDA Select carcasses compared to CONV steers. The results of this experiment show that CONV-Z and CONV production results in a significant improvement in feedlot performance and USDA YG compared to NAT