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

Calpastatin activity measured at 24 h postmortem in bovine longissimus musc le (PMLD24) is correlated with Warner-Bratzler shear force (WBS) measuremen ts, an objective measure of tenderness. A live-animal measurement of calpas tatin 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 d etermine the relationship among various calpastatin activity measures and t enderness determined by WBS and sensory panel. Biopsies (approximately 10 g ) mere obtained surgically 2 d before slaughter from the supraspinatus musc le on the anterior surface of the scapula (LISH0) from contemporary purebre d 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 postmorte m cooling process for 24 h (LISH24) prior to extraction. A rib section ante rior 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 pan el, and WBS measurements. A postmortem shoulder muscle sample (PMSH24) was collected at the same time. Calpastatin was extracted from all muscle sampl es 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 c orrelations were found between WBS and sensory panel tenderness (-.55), bet ween WBS and PMLD24 (-.43), and between LISK24 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 prod uct tenderness.