Effects of zilpaterol hydrochloride and implants in beef heifers II: aging effects on Warner-Bratzler shear force, collagen solubility, and fiber cross-sectional area
To evaluate the effects of zilpaterol hydrochloride (ZH), implants, and day of aging (DOA) on Warner-Bratzler shear force (WBSF), collagen solubility, and fiber cross sectional area (CSA), 33 crossbred heifers were blocked by weight and randomly assigned to 1 of 3 treatments: no implant or ZH (CON); Component TE-200 implant on day 1 of the study (IMP); or implant and 8.3 ppm of ZH for 21 days with a 3-d withdrawal period (ZIL). After 75 d of feeding, animals were shipped to a commercial abattoir for harvest, chilled for 36 h, and boneless strip loins were transported to the Kansas State University Meats Laboratory. To assess CSA and myosin heavy chain isoform (MHC), 13th-rib LM samples were cryopreserved, sectioned into 5-µm sections, and immunostained for MHC type I, IIA, and IIX. On d 3, 14, and 21 of aging, a 2.54-cm steak and a 0.64-cm steak were fabricated for WBSF and collagen solubility analyses, respectively. For WBSF, there was a treatment × DOA interaction (P<0.01). On d 3 of aging, CON steaks had decreased WBSF compared to IMP and ZIL steaks (P<0.01). At d 14, CON and IMP steaks did not differ (P=0.21) in WBSF, but ZIL steak WBSF values were greater than those of the other treatments (P<0.01). After 21 d aging, there were no WBSF differences between treatments (P>0.13). There was no treatment × DOA interaction for percent soluble or total collagen (P>0.20). Implants and ZIL increased the percentage of soluble collagen when compared to CON (P<0.05), and solubility of collagen also increased between d 14 and 21 of aging (P<0.01). Treatment or DOA did not affect total collagen content (P>0.51). For type I muscle fibers, CSA was greatest for the IMP group (P<0.01). Type IIA and IIX CSA were greater for ZIL compared to IMP and CON (P<0.01). There were positive correlations between type IIX CSA and WBSF on days 3, 14, and 21 of aging (R2=0.64, 0.58, and 0.37, respectively; P<0.05). Increased CSA for type I and type IIA were positively correlated with increased WBSF for d 3 and 14 (type I R2=0.51, 0.44, and 0.26; type IIA R2=0.51, 0.45, and 0.27, respectively; P<0.05), but not for d 21 (P>0.14). Implants and ZH increase the CSA of muscle fibers, which correlate positively with WBSF values.
Growth promotants, shear force, cross-sectional area