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

Abstract

ABSTRACT:The objective of the study was to examine the effect of growth-promoting technologies (GP) on Longissimus lumborum steak tenderness, muscle fiber cross-sectional area (CSA), and collagen solubility. Crossbred feedlot heifers (n = 33; initial BW 464 ± 6 kg) were blocked by BW and assigned to 1 of 3 treatments: no GP (CON; n = 11); implant, no zilpaterol hydrochloride (IMP; n = 11); implant and zilpaterol hydrochloride (COMBO; n = 11). Heifers assigned to receive an implant were administered Component TE-200 on d 0 of the study, and the COMBO group received 8.3 mg/ kg DM of zilpaterol hydrochloride for the final 21 d of feeding with a 3 d withdrawal period. Following harvest, strip loins were collected and fabricated into 4 roasts and aged for 3, 14, 21, or 35 d postmortem. Fiber type was determined by immunohistochemistry. After aging, objective tenderness and collagen solubility were measured. There was a treatment × day of aging (DOA) interaction for Warner-Bratzler shear force (WBSF; P < 0.01). At d 3 of aging, IMP and COMBO steaks had greater WBSF than CON steaks (P < 0.01). By d 14 of aging, the WBSF of IMP steaks was not different (P = 0.21) than CON steaks, but COMBO steaks had greater shear values than steaks of other treatments (P < 0.02). The COMBO steaks only remained tougher (P = 0.04) than the CON steaks following 35 DOA. Compared to CON muscles, IMP and COMBO type I and IIX muscle fibers were larger (P < 0.03). Treatment, DOA, or the two-way interactions did not impact measures of total and insoluble collagen (P > 0.31). Soluble collagen amount tended to be affected (P = 0.06) by a treatment × DOA interaction which was due to COMBO muscle having more soluble collagen than the other 2 treatments on d 21 of aging (P < 0.02). Correlation analysis indicated that type I, IIA, and IIX fiber CSA are positively correlated with WBSF at d 3 and 14 of aging (P < 0.01), but only type IIX fibers are correlated at d 21 and 35 of aging (P < 0.03). At these time periods, total and insoluble collagen became positively correlated with WBSF (P < 0.01). This would indicate that relationship between muscle fiber CSA and WBSF decreases during postmortem aging, while the association between WBSF and collagen characteristics strengthens. The use of GP negatively impacted meat tenderness primarily through increased muscle fiber CSA and not through altering collagen solubility.

Effects of anabolic implants and ractopamine-HCl on muscle fiber morphometrics, collagen solubility, and tenderness of beef longissimus lumborum steaks1,2

“…In the current study, dressing percentage and yield grade were unaffected by GP treatment. In contrast, Ebarb et al (2016) reported a tendency for dressing percentage to be increased due to GP treatment, while yield grade was decreased by 28% and 33% for carcasses from heifers implanted and heifers implanted and fed ZH, respectively. Bruns et al (2005) observed similar yield grade measures, but increased dressing percentage by 0.6% for carcasses from implanted steers fed ZH when compared to non-implanted steers.…”

“…Quinn et al (2008) reported an increase in HCW by 2% for heifers that were not implanted, but received RH during the finishing period. Ebarb et al (2016) observed 4% heavier carcasses for heifers implanted and supplemented ZH during finishing when compared to the control heifers. In the current study, dressing percentage and yield grade were unaffected by GP treatment.…”

“…Hot carcass weight tended to be affected by the use of GP, as the COMBO and IMP carcasses were approximately 4% heavier than the CON carcasses. Ebarb et al (2016) reported that carcasses from heifers implanted with the same implant tended to be 2% heavier than CON carcasses. Similarly, Boles et al (2009) administered TBA/ E 2 implants to feedlot heifers and also reported increased HCW by 2% when compared to non-implanted heifers.…”

“…The methods of Phelps et al (2014) and Ebarb et al (2016) were followed for immunohistochemical analysis. Briefly, a 1 cm × 1 cm × 1.27 cm sample was collected from the geometric center of the medial, medial/lateral, and lateral areas of the muscle.…”

“…Previous literature demonstrated GP negatively impact tenderness through increased calpastatin activity (Gerken et al, 1995;Strydom et al, 2009), but little attention has been focused on the muscle structure. Ebarb et al (2016) found the reduction in tenderness caused by GP was due to increased muscle fiber cross-sectional area (CSA), but collagen solubility was not affected by GP treatment. Roy et al (2015) reported hydroxylysyl pyridinoline (HP) crosslinks increased within the gluteus medius and semitendinosus when steers were administered an implant, but RH supplementation did not impact HP content.…”