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It is generally accepted that muscle proteins are under continual degradation during normal growth. It has been estimated that 15 to 22% of the animal's total energy expenditure is for this muscle protein turnover. Regulation of the rate of muscle protein degradation could cause dramatic changes in rate and efficiency of muscle growth. Despite their importance in muscle growth, the mechanisms and control of skeletal muscle protein degradation are unknown. It has been hypothesized that several enzyme systems are involved at different stages of degradation, and that the calpain enzyme system (which occurs naturally in muscle) may initiate protein degradation of the muscle fiber.
It has been demonstrated that β-agonists increase muscle growth. At least a part of this growth results from decreased protein degradation. β-agonists also decrease meat tenderness by increasing the activity of the calpain inhibitor, calpastatin. We know that the calpain system has a major role in postmortem tenderization of meat. We also hypothesize that the calpain system plays a major role in muscle protein degradation in the growing animal. The objective of this study was to determine the effects of a β-agonist on muscle protein degradation, muscle enzyme activity and meat tenderness of steers.