Relationships between rate of growth, endogenous muscle enzymes and meat palatability were investigated in 48 young (13 mo) Angus bulls. After backgrounding for 4 mo, bulls were placed on a high-energy diet for 30 d, at which time they were assigned randomly to one of three feeding treatments: 1) high energy (ad libitum-fed), 2) maintenance energy (restriction-fed to maintain body weight) or 3) sub-maintenance energy (restriction-fed to lose .68 kg/d). Cattle were slaughtered after 30 or 60 d on trial. Cathepsins B and H and β-glucuronidase in the longissimus muscle were quantitated at slaughter. Serum hydroxyproline, longissimus muscle collagen, taste-panel ratings and peak load for shear were obtained. Rate of growth did not influence enzyme or palatability traits and, although differences were noted for plasma hydroxyproline, muscle collagen amount and solubility were unchanged. Overall, about one-half of the variation in serum hydroxyproline, muscle collagen, taste-panel ratings and shear-force value could be explained by collective differences in selected enzyme traits. These data indicate that a significant relationship exists between proteolytic activity of longissimus muscle and meat tenderness.
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