Evaluation of calpastatin activity measures in ante- and postmortem muscle from half-sib bulls and steers

Calpastatin activity measured at 24 h postmortem in bovine longissimus muscle (PMLD24) is correlated with Warner-Bratzler shear force (WBS) measurements, an objective measure of tenderness. A live-animal measurement of calpastatin activity that correlates with 24-h postmortem activity would provide information for selection programs without the expense of progeny testing. The purpose of this study was to evaluate the effectiveness of calpastatin activity measurements obtained on tissue samples from live animals and to determine the relationship among various calpastatin activity measures and tenderness determined by WBS and sensory panel. Biopsies (approximately 10 g) were obtained surgically 2 d before slaughter from the supraspinatus muscle on the anterior surface of the scapula (LISH0) from contemporary purebred Angus bulls (n = 12) and steers (n = 17). Biopsies from a subset of these cattle (n = 12) were refrigerated at 4 degrees C to simulate the postmortem cooling process for 24 h (LISH24) prior to extraction. A rib section anterior to the 12 and 13th rib interface was collected from all animals at the commercial abattoir between 22 and 23 h postmortem for PMLD24, sensory panel, and WBS measurements. A postmortem shoulder muscle sample (PMSH24) was collected at the same time. Calpastatin was extracted from all muscle samples using a heated calpastatin activity protocol. Sensory panel tenderness, WBS, LISH0, LISH24, and PMSH24 were not different between bulls and steers. However, PMLD24 values were significantly different. Significant partial correlations were found between WBS and sensory panel tenderness (-.55), between WBS and PMLD24 (-.43), and between LISH24 and PMLD24 (.78). Therefore, similar calpastatin activity values are possible with ante- and postmortem tissue samples, suggesting the possibility of using measurements from live-tissue biopsies from other than the longissimus muscle to predict end product tenderness.