Tenderness of normal and callipyge lamb aged fresh or after freezing(∗)

The present experiments were conducted to determine if tenderness differed between normal (N) and callipyge (CLPG) lamb during post-mortem aging of: (1) longissimus muscle (LM), (2) semimembranosus muscle (SM), and (3) LM after freezing for 6 weeks. In the LM, CLPG chops were tougher (p < 0.01) than N at every post-mortem age and after 24 h CaCl(2) marination of a day 1 chop. Post-mortem aging reduced (p < 0.05) shear force of the LM in both N and CLPG; however, this reduction proceeded at a slower rate (-0.127 vs -0.341 kg d(-1); p = 0.01) and for a longer time period (24 vs 6 days; p < 0.05) in CLPG than N. In the SM muscle, shear force values did not differ (p > 0.05). due to phenotype, post-mortem age, or the two-way interaction. Freezing prior to aging accelerated the rate of post-mortem tenderization in CLPG (-0.130 vs -0.060 kg d(-1); p = 0.004) while no changes (p > 0.05) were observed for N. Phenotypic expression of the CLPG gene increased the toughness of the LM with no change in SM; however, freezing prior to aging accelerated the post-mortem tenderization process in CLPG LM.