title: Effects of ractopamine supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type.
abstract: Effects of ractopamine hydrochloride (RAC) supplementation on growth performance and carcass characteristics of feedlot steers differing in biological type were investigated using British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 420). Steers of each type were weighed at reimplantation [British, mean BW = 375 kg (SD = 38 kg); Continental crossbred, mean BW = 379 kg (SD = 42 kg); Brahman crossbred, mean BW = 340 (SD = 32 kg)] and sorted into 7 BW blocks, each block consisting of 2 pens (10 steers per pen) per type. Pens within a block x type subclass were randomly assigned to RAC treatments (0 or 200 mg x steer(-1) x d(-1) fed during the final 28 d of the finishing period). The type x RAC interaction did not affect (P > 0.05) any of the traits evaluated in this study. Feeding RAC improved (P = 0.001) ADG (1.50 vs. 1.73 +/- 0.09 kg) and G:F (0.145 vs. 0.170 +/- 0.005), but did not affect (P = 0.48) DMI of steers. Dressing percentage, adjusted fat thickness, KPH percentage, and yield grade were not affected by RAC supplementation. Carcasses of steers fed RAC had heavier (P = 0.01) HCW (359 vs. 365 +/- 4.9 kg), larger (P = 0.046) LM areas (81.7 vs. 84.0 +/- 1.1 cm(2)), and tended (P = 0.07) to have lower mean marbling scores (487 vs. 477 +/- 5.2; Slight = 400, Small = 500) than did carcasses of control steers. Among the 3 biological types, Brahman crossbred steers had the lowest DMI and produced the lightest-weight carcasses that had the lowest mean marbling score (P < 0.05). Compared with Continental crossbred and Brahman crossbred steers, British steers produced carcasses with the greatest (P = 0.001) mean marbling scores. Continental crossbred steers had the heaviest BW and greatest dressing percentages and produced the heaviest carcasses with the largest LM areas (P < 0.05) compared with British and Brahman crossbred steers. In the present study, 28 d of supplementation with RAC at a dosage rate of 200 mg x steer(-1) x d(-1) elicited consistent responses in growth performance and carcass traits among 3 diverse biological cattle types.
authors: Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171, USA.
authors: S L
authors: SL
authors: Gruber
authors: J D
authors: JD
authors: Tatum
authors: T E
authors: TE
authors: Engle
authors: M A
authors: MA
authors: Mitchell
authors: S B
authors: SB
authors: Laudert
authors: A L
authors: AL
authors: Schroeder
authors: W J
authors: WJ
authors: Platter
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D002417:Cattle / Q000235:genetics* / Q000254:growth & development*; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D002149:Energy Intake / Q000502:physiology; D008297:Male; D008460:Meat / Q000592:standards; D010627:Phenethylamines / Q000494:pharmacology*; D011897:Random Allocation; D015430:Weight Gain / Q000187:drug effects*
chemical_list: D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; C060897:ractopamine