Effects of sequential feeding of β-adrenergic agonists on cull cow performance, carcass characteristics, and mRNA relative abundance

• Published in: Journal of animal science 2012-05, Vol.90 (5), p.1628-1637
• Main Authors: Weber, M. J, Dikeman, M. E, Unruh, J. A, Jaeger, J. R, Murray, L, Houser, T. A, Johnson, B. J
• Format: Article
• Language: English
• Subjects: Adrenergic beta-Agonists - administration & dosage; Adrenergic beta-Agonists - economics; Adrenergic beta-Agonists - pharmacology; agonists; Anabolic Agents - administration & dosage; Anabolic Agents - pharmacology; Animal Feed - economics; Animals; Body Composition - drug effects; carcass characteristics; Cattle - physiology; color; cows; diet; Drug Combinations; economic valuation; Estradiol - administration & dosage; Estradiol - pharmacology; Estrogens - administration & dosage; Estrogens - pharmacology; Female; Gene Expression Regulation - drug effects; industry; intramuscular fat; markets; messenger RNA; myosin heavy chains; Phenethylamines - administration & dosage; Phenethylamines - economics; Phenethylamines - pharmacology; Real-Time Polymerase Chain Reaction; Receptors, Adrenergic, beta - genetics; Receptors, Adrenergic, beta - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; slaughter; Trenbolone Acetate - administration & dosage; Trenbolone Acetate - pharmacology; Trimethylsilyl Compounds - administration & dosage; Trimethylsilyl Compounds - economics; Trimethylsilyl Compounds - pharmacology; Weight Gain; white adipose tissue
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2011-4285

The objectives of this study were to determine the effects of supplementation with a single β-adrenergic agonist (β-AA) or a sequence of β-AA on cow performance, carcass characteristics, and mRNA relative abundance of cull cows implanted and fed a concentrate diet. Sixty cull cows were implanted with Revalor-200 (200 mg of trenbolone acetate and 20 mg of estradiol) and assigned to 1 of 4 treatments (n = 15/treatment): CON = fed a concentrate diet only; RH = supplemented with ractopamine-HCl for the last 25 d before slaughter; ZH = supplemented with zilpaterol-HCl for 20 d before a 3-d withdrawal before slaughter; RH + ZH = supplemented with RH for 25 d, followed by ZH for 20 d before a 3-d withdrawal before slaughter. Ractopamine-HCl was supplemented at a dose of 200 mg·animal–1·d–1, and ZH was supplemented at 8.33 mg/kg (100% DM basis) of feed. All cows were fed a concentrate diet for 74 d. Each treatment had 5 cows per pen and 3 replicate pens. Body weights were collected on d 1, 24, 51, and 72. Muscle biopsies from the LM were collected on d 24, 51, and at slaughter from a subsample of 3 cows per pen. Carcass traits were evaluated postslaughter. The 2 ZH treatments averaged 15.3 kg more BW gain, 0.20 kg greater ADG, and 7.8 cm2 larger LM area than CON and RH treatments, and 21 kg more HCW than CON, but these differences were not significant (P > 0.10), likely due to a sample size of n = 15/treatment. The sequence of RH followed by ZH tended to optimize the combination of HCW, LM area, percent intramuscular fat, and lean color and maturity compared with the ZH treatment. Abundance of β2-adrenergic receptor (AR) mRNA was not altered in the RH + ZH treatment during RH supplementation from d 24 to 51 of feeding. However, the abundance of β2-AR mRNA increased (P < 0.05) the last 23 d of feeding for the RH treatment and tended (P = 0.10) to increase in ZH cows during ZH supplementation. For all cows, abundance of type IIa myosin heavy chain (MHC-IIa) mRNA decreased (P < 0.05) after 24 d of feeding. Abundance of MHC-IIx mRNA increased (P < 0.05) for ZH and RH + ZH treatments the last 23 d of feeding during ZH supplementation. Although few significant differences were observed in performance or carcass traits, mRNA quantification indicated that β-AA supplementation elicited a cellular response in cull cows. Implanting and feeding cull cows for 74 d, regardless of β-AA supplementation, added economic value by transitioning cows from a cull cow to what is referre