title: Effect of the administration program of 2 β-adrenergic agonists on growth performance and carcass and meat characteristics of feedlot ram lambs.
abstract: The aim of the study was to determine the effects of 3 feeding dose programs of the β-adrenergic agonists (β-AA) ractopamine hydrochloride (RH) or zilpaterol hydrochloride (ZH) for the final 30 d before slaughter on growth performance and carcass and meat characteristics of feedlot ram lambs. Eighty-four Dorper × Katahdin ram lambs (30.0 ± 1.6 kg) were blocked by BW and randomly assigned to pens (4 lambs per pen and 3 pens per treatment). Pens within a block were assigned randomly to 1 of 7 dietary treatments: 1) control (CTL) = diet without β-AA; 2) RH constant (RHC) = 20.0 mg/kg of RH, d 1 to 30; 3) RH increasing (RHI) = 10.0 mg/kg, d 1 to 10; 20.0 mg/kg, d 11 to 20; and 30.0 mg/kg, d 21 to 30; 4) RH decreasing (RHD) = 30.0 mg/kg, d 1 to 10; 20.0 mg/kg, d 11 to 20; and 10.0 mg/kg, d 21 to 30; 5) ZH constant (ZHC) = 6.0 mg/kg of ZH, d 1 to 30; 6) ZH increasing (ZHI) = 3.0 mg/kg, d 1 to 10; 6.0 mg/kg, d 11 to 20; and 9.0 mg/kg d 21 to 30; and 7) ZH decreasing (ZHD) = 9.0 mg/kg, d 1 to 10; 6.0 mg/kg, d 11 to 20; and 3.0 mg/kg, d 21 to 30. Overall, β-AA supplementation reduced DMI (P < 0.001) compared with CTL lambs, but lambs fed RHI and ZHI programs had greater (P < 0.05) total BW gain, ADG, and G:F. Carcass weight was improved (P < 0.05) by RHI and ZHI programs, but dressing percentage was enhanced (P < 0.05) by only ZHC or ZHI treatments. Fat thickness and yield grade were reduced (P < 0.05) by ZH or RH regardless of feeding program. Most LM characteristics (pH, moisture loss, and chemical composition) were not different among treatments (P > 0.05), with the exception of fat content that was reduced (P < 0.001) in lambs fed β-AA, and diameter of muscle fibers that was increased (P < 0.05) by ZHI treatment. Constant and increasing doses of ZH reduced (P < 0.05) the a* value of LM and semitendinosus muscles, with no effects on L* or b* values. The mass of liver was reduced (P < 0.05) in ZHI-treated lambs compared with CTL lambs, and plasma urea concentration was reduced (P < 0.05) by RH or ZH administration regardless of feeding program, although there were no other differences in organ mass weight (P ≥ 0.35) or blood metabolites (P ≥ 0.16). Increasing doses of RH or ZH augmented the growth performance response without negative effects on organ mass weight or blood metabolites. Although a ZHI program improved carcass characteristics, the increased LM fiber diameter of lambs fed ZHI program could be unfavorable because of the potential negative effect on tenderness.
authors.affiliation: Faculty of Biological Sciences, Autonomous University of Nuevo Leon, Nuevo Leon, 66450, México.
authors.forename: M A
authors.initials: MA
authors.lastname: López-Carlos
authors.forename: R G
authors.initials: RG
authors.lastname: Ramírez
authors.forename: J I
authors.initials: JI
authors.lastname: Aguilera-Soto
authors.forename: H
authors.initials: H
authors.lastname: Rodríguez
authors.forename: C F
authors.initials: CF
authors.lastname: Aréchiga
authors.forename: F
authors.initials: F
authors.lastname: Méndez-Llorente
authors.forename: J J
authors.initials: JJ
authors.lastname: Chavez
authors.forename: C A
authors.initials: CA
authors.lastname: Medina
authors.forename: J M
authors.initials: JM
authors.lastname: Silva
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000033:anatomy & histology / Q000187:drug effects; D008297:Male; D008460:Meat / Q000032:analysis / Q000592:standards*; D009929:Organ Size / Q000187:drug effects; D010627:Phenethylamines / Q000494:pharmacology*; D012756:Sheep; D014297:Trimethylsilyl Compounds / Q000494:pharmacology*; D014867:Water; D015430:Weight Gain / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; D014297:Trimethylsilyl Compounds; C475840:Zilpaterol; D014867:Water; C060897:ractopamine