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This Article Full Text (PDF) All Versions of this Article: jas.2009-1818v1 87/11/3686    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Rathmann, R. J. Articles by Miller, M. F. PubMed PubMed Citation Articles by Rathmann, R. J. Articles by Miller, M. F.

Effects of duration of zilpaterol hydrochloride and days on the finishing diet on carcass cutability, composition, tenderness and skeletal muscle gene expression in feedlot steers

R. J. Rathmann^*, J. M. Mehaffey^*, T. J. Baxa, W. T. Nichols, D. A. Yates, J. P. Hutcheson, J. C. Brooks^*, B. J. Johnson^* and M. F. Miller^*

^* Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409 , Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506 Intervet Schering Plough Animal Health, DeSoto, KS 66018

ryan.rathmann{at}ttu.edu

Abstract

Pre-selected carcasses (n = 112) from feedlot steers fed zilpaterol hydrochloride (ZH; 8.33 mg/kg, DM basis) in a serial slaughter experiment were evaluated to determine the effects of ZH upon carcass cutability, composition, and tenderness. A 4 x 4 factorial arrangement of treatments in a completely random design was used with days on ZH (0, 20, 30, and 40 d before slaughter with a 3-d withdrawal) and days on the finishing diet (DOF; 136, 157, 177 and 198 d). No relevant ZH duration x slaughter group interactions were detected (P > 0.05) for carcass cutability, composition, or tenderness data. Exposure to ZH increased the lean yield of 22 of the 33 subprimals evaluated with every subprimal within the round showing increased cutability (P 0.04). Carcass fat was decreased, while carcass protein and moisture was increased due to ZH (P < 0.01). Lengthening the ZH feeding period did not result in additive gains in subprimal yield or chemical composition (P > 0.05). Warner-Bratzler shear force (WBSF) analysis of the LM indicated that ZH caused a toughening effect (P < 0.01) regardless of the length of the aging period (7, 14, or 21 d). Extending the ZH dose duration caused a linear increase in WBSF at 7 (P = 0.06) and 21 d (P < 0.01) of aging. Within 10 min postmortem, samples (n = 48) were collected from the semimembranosus muscle for RNA isolation from 4 randomly selected steers from each treatment within the 157, 177, and 198 d slaughter groups. Feeding ZH did not alter β1- or β2-adrenergic receptor (β-AR), calpastatin (CAL), IGF-I, or myosin heavy chain (MHC) isoform I mRNA abundance (P > 0.10). There was a ZH duration x DOF interaction (P < 0.01) for the expression of MHC-IIa and -IIx. Expression of MHC-IIa was decreased in every ZH treatment within the 177 and 198 DOF groups (P < 0.02). Expression of MHC-IIx was increased in the 20 d ZH group in the 157 DOF group (P = 0.03), and the 40 d ZH group in the 177 (P = 0.10) and 198 (P = 0.03) DOF groups. There was a tendency for a linear decrease in CAL mRNA abundance as ZH duration increased (P = 0.07), and there was a linear increase in β2-AR (P = 0.03) and CAL (P < 0.01) mRNA abundance as DOF increased. Collectively, the data indicate that ZH may influence net protein turnover by decreasing MHC-IIa mRNA transcription and possibly increasing MHC-IIx. Furthermore, a ZH feeding duration of 20 d appeared to be adequate for capturing lean yield benefits while limiting tenderness losses.

Key Words: Beta-adrenergic agonist • zilpaterol hydrochloride • days on feed • carcass cutout • myosin • steer