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Effect of 25‐hydroxyvitamin D3 and dietary calcium on calpastatin activity in beef muscles

Increasing Ca concentration in muscle of beef animals at the time of harvest has been hypothesized to increase calpain activity improve beef tenderness. We hypothesized that Ca concentrations and muscle protein degradation would be increased in muscles from the round section of cows fed dietary treatments designed to manipulate muscle Ca. Our objective was to determine the effect of 25‐hydroxyvitamin D3 (25‐OH D3) and dietary Ca manipulations on predictors of meat tenderness. During our 46‐d study, 27 Angus cows (3–7 y) were fed a corn‐based diet and had dietary Ca withdrawn from the diet then replenished at 0.5, 0.75, or 1.0 % of diet dry matter. Also, 0, 250, or 500 mg of 25‐OH D3 was administered to each cow 7 d before harvest. Seven muscles, adductor, gracillus, pectineus, sartorius, semimembranosis, vastus intermedius, and vastus lateralis, were dissected 1 d after harvest. Each muscle was cut into 2.54‐cm steaks and aged for 1, 3, or 7 d at 4°C and then frozen at −20°C. Ca concentrations were increased in muscle from cows treated with 25‐OH D3 and higher dietary Ca concentrations (P<0.05). Although no significant differences in protein degradation exists between treatments, a strong positive correlation (R2=0.30–0.80) exists between Ca concentration in muscle and protein degradation after 3 and 7 d of ageing in the pectineus, adductor, and vastus intermedius muscles. These results indicate that treatment with 25‐OH D3 and dietary Ca manipulations increases proteolysis in muscles from cows, and this increase is probably because of increased calpain activity. NCBA Proposal No. 04‐1664.