599
Effect of 300 or 400 mg daily of ractopamine hydrochloride on growth performance and carcass characteristics of finishing steers during the last 14, 28, or 42 days
Crossbred yearling steers (n=576; BW = 408 ± 29 kg) were utilized in a randomized block design (n=4 BW blocks) with a 3 x 3 factorial treatment design to study the effects of ractopamine hydrochloride (RAC) dosage and duration on growth performance. Factors included RAC feeding duration (14, 28, or 42 d prior to harvest) and RAC dosage (0, 300, and 400 mg/hd/d). During the treatment phase, RAC dose was top-dressed daily using fine-ground corn as the carrier. There were no significant duration x dosage interactions (P > 0.07) for growth performance or carcass characteristics; however, simple effects will be presented. Live final BW was not different (P > 0.44) for steers fed 0, 300, or 400 mg RAC for 14 d. At 28 d, steers fed RAC at 400 mg were significantly (P < 0.01) heavier than steers receiving 0 mg. There was a tendency at 28 d for increased live final BW for steers fed RAC at 300 mg (P = 0.07) compared to 0 mg and steers fed 400 mg of RAC compared to 300 mg (P = 0.07). Live final BW was greater (P < 0.01) for steers fed RAC for 42 d at 300 and 400 mg compared to cattle receiving 0 mg; however, live final BW was similar (P = 0.57) between 300 and 400 mg of RAC. Between treatments, DMI was similar (P = 0.27). Hot carcass weight was similar (P = 0.33) between yearlings fed 0 and 300 mg of RAC for 14 d, but tended to be greater (P = 0.07) for steers fed 400 mg of RAC compared to 0 mg. Hot carcass weight was greater (P < 0.01) for steers fed 300 and 400 mg of RAC compared to cattle fed 0 mg for 28 d. Carcasses from yearlings fed RAC for 42 d at 300 and 400 mg were heavier (P < 0.01) than 0 mg fed steers. Feeding 300 mg of RAC for 28 or 42 d increased live final BW by 7 and 13 kg, while feeding RAC at 400 mg resulted in 14 and 11 kg increases relative to control steers. Feeding 300 mg of RAC for 28 or 42 d would suggest 4.9 and 7.5 kg improvements in HCW, while feeding 400 mg of RAC would suggest 8.7 and 9.3 kg heavier carcasses compared to steers fed no RAC.
Keywords: dose, duration, ractopamine