The calpain-calpastatin system plays a key role in skeletal muscle growth and development processes. It is known that calpastatin activity correlates highly with muscle growth rate, which implies that skeletal muscle growth is likely to result from reduced protein degradation due to compromised activity of calpains or substantial increase of calpastatin activity. The objective of the present research was to identify polymorphic forms in intron 12 of the ovine calpastatin gene in sheep of synthetic lines BCP and SCP, followed by determination of the correlation between each polymorphic form of