Effect of the administration program of 2 β-adrenergic agonists on growth performance and carcass and meat characteristics of feedlot ram lambs

• Published in: Journal of animal science Vol. 90; no. 5; pp. 1521 - 1531
• Main Authors: López-Carlos, M A, Ramírez, R G, Aguilera-Soto, J I, Rodríguez, H, Aréchiga, C F, Méndez-Llorente, F, Chavez, J J, Medina, C A, Silva, J M
• Format: Journal Article
• Language: English
• Published: United States 01-05-2012
• Subjects: Adrenergic beta-Agonists - pharmacology; Animals; Body Composition - drug effects; Hydrogen-Ion Concentration; Liver - anatomy & histology; Liver - drug effects; Male; Meat - analysis; Meat - standards; Organ Size - drug effects; Phenethylamines - pharmacology; Sheep; Trimethylsilyl Compounds - pharmacology; Water; Weight Gain - drug effects
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2010-3513

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.