title: The effect of zilpaterol hydrochloride supplementation on energy metabolism and nitrogen and carbon retention of steers fed at maintenance and fasting intake levels.
abstract: An indirect calorimetry trial examined energy metabolism, apparent nutrient digestibility, C retention (CR), and N retention (NR) of cattle supplemented with zilpaterol hydrochloride (ZH). Beef steers ( = 20; 463 ± 14 kg) blocked ( = 5) by weight and source were individually fed and adapted to maintenance energy intake for 21 d before allotment to ZH (90 mg/steer∙d) or no β-adrenergic agonist treatment (control [CONT]) for 20 d (455 ± 14 kg at the start of treatment). Respiration chambers = 4 were used to quantify heat production (HP) during maintenance (d 12 to 16 of the ZH period) and fasting heat production (FHP; d 19 to 20 of ZH period; total 4 d of fast). Steers were harvested after a 6-d ZH withdrawal and carcasses were graded 24 h after harvest. Control cattle lost more BW ( < 0.01; 9 kg for CONT and 2 kg for ZH-treated) during maintenance whereas the BW loss of ZH-treated steers was greater ( < 0.01; 9 kg for ZH-treated and vs. 4 kg, for CONT) during FHP; no differences ( ≥ 0.76) were detected for G:F, ADG, and end BW. No differences in DMI, apparent nutrient digestibility, O consumption, or CH production ( ≥ 0.12) were detected; however, ZH-treated cattle had greater CO production during maintenance ( = 0.04; 23.6 L/kgBW for ZH-treated and 22.4 L/kg BW for CONT). Digestible energy and ME did not differ ( ≥ 0.19); however, urinary energy was greater ( = 0.05; 0.091 Mcal for CONT and 0.074 Mcal for ZH-treated) in CONT cattle. Steers treated with ZH tended to have greater HP ( = 0.09; 12.44 Mcal for ZH-treated and 11.69 Mcal for CONT), but the effect was reduced on a BW basis ( = 0.12; 0.126 Mcal/kg BW0.75 for ZH-treated and 0.120 Mcal/kg BW0.75 for CONT vs. 0.120 Mcal/kg BW). No treatment difference in FHP was observed ( ≥ 0.32) although CO production (L/steer) increased with ZH treatment ( = 0.04; 1,423 L/steer for ZH-treated and 1,338 L/steer for CONT). Control cattle excreted more ( = 0.05) N in urine (39.8 g/d for CONT and 32.4 g/d for ZH-treated); therefore, NR ( = 0.07; 22.14 g/d for ZH-treated and 14.12 g/d for CONT steers) tended to be greater for ZH-fed steers. Steers treated with ZH lost more C via CO ( = 0.04; 1,036.9 g/d for ZH-treated and 974.3 g/d for CONT) although total CR did not differ ( ≥ 0.23). Empty BW, HCW, and harvest yields (g/kg empty BW) were not different ( ≥ 0.13), whereas ZH increased dressed yield ( = 0.02; 62.12 % for ZH-treated and 60.65% for CONT) and LM area ( = 0.02; 77.81 cm for ZH-treated and vs. 70.90 cm for CONT). Separable carcass lean and actual skeletal muscle protein (SMP) were increased with ZH ( ≤ 0.04; 201.6 and 41.2 kg, respectively for ZH-treated and 196.0 and 38.4 kg, respectively for CONT). Results from this trial indicate that ZH treatment increased ( = 0.03) SMP and tended ( ≥ 0.07) to increase NR and modify HP during maintenance by increasing CO production.
authors.forename: L J
authors.initials: LJ
authors.lastname: Walter
authors.forename: N A
authors.initials: NA
authors.lastname: Cole
authors.forename: J S
authors.initials: JS
authors.lastname: Jennings
authors.forename: J P
authors.initials: JP
authors.lastname: Hutcheson
authors.forename: B E
authors.initials: BE
authors.lastname: Meyer
authors.forename: A N
authors.initials: AN
authors.lastname: Schmitz
authors.forename: D D
authors.initials: DD
authors.lastname: Reed
authors.forename: T E
authors.initials: TE
authors.lastname: Lawrence
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001823:Body Composition; D001835:Body Weight; D002244:Carbon / Q000378:metabolism*; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements; D004435:Eating; D002149:Energy Intake; D004734:Energy Metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects; D009584:Nitrogen / Q000378:metabolism*; D014297:Trimethylsilyl Compounds / Q000494:pharmacology*
chemical_list: D000318:Adrenergic beta-Agonists; D014297:Trimethylsilyl Compounds; C475840:Zilpaterol; D002244:Carbon; D009584:Nitrogen