Effects of duration of zilpaterol hydrochloride and days on the finishing diet on carcass cutability, composition, tenderness, and skeletal muscle gene expression in feedlot steers1

Abstract

Preselected 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 < or = 0.04). Carcass fat was decreased, whereas carcass protein and moisture were 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 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 Warner-Bratzler shear force 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 beta1- or beta2-adrenergic receptor (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 beta2-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.

Effect of growth-promoting technologies on Longissimus lumborum muscle fiber morphometrics, collagen solubility, and cooked meat tenderness12

“…Carcasses from ZH heifers had 35% less BF, but there was no effect on marbling score. The reduction in BF was much greater than the 5% reduction reported by Rathmann et al (2009), but these authors also found no effect on marbling. In contrast, Montgomery et al (2009) reported that BF thickness was unaffected by ZH, but marbling score was reduced instead.…”

“…Kellermeier et al (2009) conducted a similar study in steers and reported that average muscle fiber diameter increased by 3% and 6% when anabolic implants and ZH were utilized, respectively. While Rathmann et al (2009) and Baxa et al (2010) did not directly measure fiber CSA or diameter, they did indicate increases in the mRNA expression of type IIX muscle fibers demonstrated ZH increased protein synthesis of this isoform. Other B-AA have also increased muscle fiber CSA.…”

Effects of ractopamine hydrochloride and dietary protein content on performance, carcass traits and meat quality of Nellore bulls

“…This increase in muscle mass is attributed to an increase in muscle protein synthesis, a reduction in protein degradation or some combination of both (Scramlin et al, 2010). In addition, other β-AA increase the transcriptional activity of calpastatin (Rathmann et al, 2009), which could be the reason for the reduction in tenderness that has been reported in some studies (Leheska et al, 2008;Kellermeier et al, 2009).…”

Effect of feeding Zilpaterol hydrochloride for 20 days to calf-fed Holstein steers with a 3 or 10 day withdrawal period antemortem on carcass characteristics and tenderness

“…It is believed that with the feeding of BAAs the amount of the specific enzymes are changed causing an increase in the enzyme calpastatin, which is an enzyme that decreases enzymatic turnover. Alternatively Rathmann et al (2009) observed no changes in enzymatic activity with ZH fed cattle when compared to control. The author suggested that the difference in WBS from cattle fed ZH may be from an increase in myosin heavy chain proteins which correlates with the observed hypertrophy of muscling.…”

“…Generally, an increase in muscle fiber diameter (hypertrophy) will result in tougher meat. Rathmann et al (2009) reported that an increase in Warner Bratzler Shear force was likely due to the swelling of the muscle fiber (hypertrophy), this was evident because of the increase in myosin heavy chain proteins rather than a change in the protease enzyme activity within the muscle. Along with tenderness, evaluation of color is also a key aspect for determining meat quality.…”