Calpain system (l- and m-calpain, calpastatin) and myofibril fragmentation index (MFI) were analysed on muscle longissimus thoracis et lumborum of 16 male fallow deer, half 18- and half 30-month-old, slaughtered after a 4-month feeding trial on pasture alone or with concentrate supplement. Diet did not produce any difference on the measured variables. The muscle of the elder deer had a higher calpastatin level 6 h post-mortem (136.0 vs. 99.7 units/50 g, for the 30- and 18-months-old, respectively), and a lower MFI value, particularly 24 h post-mortem (71.1 vs. 89.1). This is in agreement with previous data showing tougher meat from 30-month-old animals.
