Heritabilities and phenotypic and genetic correlations for bovine postrigor calpastatin activity and measures of meat tenderness and muscle growth

The objectives of the present study were (1) to determine the heritability (h{dollar}sp2{dollar}) of bovine postrigor calpastatin activity and the phenotypic (r{dollar}sb{lcub}rm p{rcub}{dollar}) and genetic (r{dollar}sb{lcub}rm g{rcub}{dollar}) correlation coefficients between bovine postrigor calpastatin activity and measures of meat tenderness and muscle growth and (2) to determine the relationship of longissimus muscle pH at three hours postmortem to meat tenderness. The steers (n = 555) sampled for this experiment were from two different animal breeding projects and represented 31 different breed-types. Steers were fed a high-energy diet from weaning to slaughter at 385 to 450 d of age. Steers were slaughtered serially, at a commercial beef processing facility, in four slaughter groups spanning 63 d. Longissimus muscle samples were extracted at 24 to 31 h postmortem to determine calpastatin activity. Restricted maximum likelihood procedures were used to analyze these data under an animal model with fixed effects of population and slaughter group and random effects of breed within population and sire within breed within population. Calpastatin activity was highly heritable (.70 {dollar}pm{dollar}.23), and the genetic correlation between calpastatin activity and Warner-Bratzler shear force was strong (.58 {dollar}pm{dollar}.20). Moreover, calpastatin activity was correlated negatively with average daily gain and retail product weight. Thus, it may be possible to improve beef tenderness via selection against calpastatin activity without detrimental effects on production efficiency. Longissimus muscle pH at three hours postmortem was correlated lowly (r = {dollar}-{dollar}.11) with Warner-Bratzler shear force at seven days postmortem. Moreover, analysis of variance indicated that when carcasses were segmented according to longissimus muscle pH, there were no differences in tenderness among the subclasses. Thus, muscle pH at three hours postmortem should not be included in a beef quality grading system.