Meat samples (M. longissimus dorsi) from a control Angus herd (ACO) and associated selection herd (AS1) were compared for calpain/calpastatin concentrations and shear-force tenderness, after the herds had been subjected to 22 to 24 years of random replacement or selection for increased adjusted yearling weight. The objective was to monitor changes in meat tenderness at fixed slaughter date resulting from genetic selection, and associated changes in muscle calpain or calpastatin concentrations. Bull calves (n=94), from 3 successive calf crops raised on pasture, were slaughtered immediately after arrival at the abattoir at about 20 months of age on one day each year (May 1995, 1996 and 1997). Carcasses were electrically stimulated, weighed and hot boned. Meat samples for calpain/calpastatin analysis were taken within 30 minutes of slaughter from the M. longissimus dorsi, with further samples after 24 hr of ageing at 10°C. Shear-force tenderness was assessed on the same muscle at intervals from 24 hr until one month of ageing at -1°C. Calpastatin, milli- and micro-calpain activities were assayed using casein as a substrate. Yearling live weights, hot carcass weights and muscle weights were respectively 19.0%, 16.5% and 17.3% greater in the AS1 than the ACO herd (all P<0.001). The AS1 samples were on average 8 to 16% more tender than ACO samples (P<0.05) on days 1 and 3 post mortem, but there were no significant herd differences in tenderness at later ageing times. The between-animal repeatability of shear-force tenderness from days 1 to 28 was 0.44±0.07. Millicalpain concentrations were significantly lower in the AS1 than ACO samples by an average of 13% (P<0.001), and there were smaller differences in microcalpain and calpastatin between herds in the same direction. These results show that early post mortem tenderness, millicalpain and possibly microcalpain and calpastatin concentrations were associated with genetic differences in growth.

CA, Morris, PA Speck, NG Cullen, and PM Dobbie

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 214-217, 1998
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