Blood metabolites, meat quality and muscle calpain-calpastatin activities in goats treated with low doses of recombinant bovine somatotropin

Growing female Alpine goats (n = 14; 6 month of age; BW of 18 +/- 2.7 kg) were used in a 10-week experiment to assess the effect of daily injection of a low dose (40 microgram/kg of BW) of recombinant bovine somatotropin (rbST) on blood metabolite concentrations, mass of the visceral organs, the calpain system, and chevon quality. Goats were randomly assigned to either a control (0.9% saline; n = 7) or a treatment group (n = 7) receiving a daily dose of rbST. All animals were fed a 16% CP and 2.9 Mcal/kg DE alfalfa based-diet ad libitum. Blood samples were collected every 2 weeks for a 10-week period and analyzed for glucose, NEFA, and PUN. At the end of the 10-week period, animals were sacrificed and processed. A portion of the loin muscle was removed, trimmed of fat, denuded and homogenized in an extraction buffer for determination of the calpain-calpastatin system. Components of the viscera were separated and individually weighed. The carcass was chilled for 24 h at 2 degrees C. Before cooking the loin/rib chops, instrumental color measurements were done after 45 min bloom. Shear values were determined on cooked chops. Plasma non-esterified fatty acid concentrations were influenced by treatment (P < 0.01), sampling time (P < 0.01), and treatment x sampling time interaction (P < 0.01). Plasma glucose and PUN concentrations increased over sampling time (P < 0.01). At the end of the 10-week treatment period, PUN was higher in goats treated with rbST than in controls. Body weight change, carcass weight, visceral mass, and loin eye area were not influenced by rbST treatment. Mean m-calpain, mu-calpain, and calpastatin activities (caseinolytic units per 50 g of tissue), as well as pre-aging instrumental color (L*, a*, b*, chroma and Hue) values were also not affected by rbST injections. While treatment or treatment x aging time interaction did not influence cooking loss, aging decreased (P < 0.01) shear value but without significant improvement beyond 7 days. There was a positive correlation between longissimus muscle final pH and m-calpain activities in both bST-treated and control goats (P < 0.05), although the relationship between final pH and calpastatin activities was much stronger (P < 0.02). Daily injection of a low dose of rbST did not alter the meat quality, muscle calpain system, or weights of visceral organs.