The early post mortem expression of eight genes potentially involved in meat ageing process and the tenderness of two Italian Simmental young bulls' (Bos taurus) skeletal muscles differing in their contractile type were evaluated. Samples of Longissimus lumborum (LL) and Infraspinatus (IS) muscles were collected from 17 bulls. The messenger RNA (mRNA) abundances of calpain-1, calpain-2, calpastatin, caspase 3, caspase 9, heat shock protein 27 (Hsp27), Hsp40 and Hsp70 were detected by quantitative PCR. The myosin heavy chain-slow and -fast isoform content, the pH48h and the lipid content of the muscles were in line with the contractile and metabolic type. In comparison with the fast LL, the slow IS showed a lower calpain-1/calpastatin mRNA content ratio after slaughtering and a higher Warner-Bratzler Initial Yield value after 7 days of ageing. Hsp27 and Hsp70 mRNA abundances were significantly lower in LL than IS, highlighting their potential role in the ageing process of bovine muscles.
