COMPARISON OF CALPAIN AND CALPASTATIN ACTIVITIES IN SKELETAL-MUSCLE OF BROILER AND LAYER CHICKENS

1. The objective of this study was to estimate the difference between broiler and layer chicks in the activities of calpain and calpastatin (inhibitor of calpain) in breast muscle. Differences between broilers and layers in body weight, daily gain at 3 weeks of age and fractional growth rate (FGR) during 2 and 3 weeks of age were statistically significant (P < 0.01). 2. Calpain and calpastatin activities were measured at three weeks of age with alkali-denatured casein as a substrate. The m-calpain (calpain activated by millimolar calcium concentration) activities in units/g muscle and units/mg extractable muscle protein were 0.779 and 0-353 for broilers, and 1-042 and 0.440 for layers, respectively. The calpastatin activities in units/g muscle and units/mg extractable muscle protein were 0-332 and 0.153 for broilers, and 0-262 and 0.112 for layers, respectively. 3. Broilers with high FGR showed low m-calpain and high calpastatin activities. In contrast, layers with low FGR showed high m-calpain and low calpastatin activities. 4. These results suggest that m-calpain and calpastatin activities in skeletal muscle vary between breeds which have different rates of muscle production.