Effect of the callipyge gene on muscle growth, calpastatin activity, and tenderness of three muscles across the growth curve

Changes in muscle growth, calpastatin activity, and tenderness of three mus cles were assessed in 20 callipyge and 20 normal wether lambs slaughtered a t live weights (LW) of 7, 20, 36, 52, and 69 kg. At 24 h postmortem, the lo ngissimus (LM), semimembranosus (SM), and supraspinatus (SS) muscles were r emoved and weighed and samples were obtained for calpastatin activity (CA; 24 h) and Warner-Bratzler shear force (WBS; aged 6 d). For muscle weights a nd calpastatin activity, the weight group x muscle x phenotype interaction was significant (P < 0.05). Muscle weights were similar (P > 0.05) between phenotypes for all three muscles at 7 kg LW. At 20 kg LW, the LM and SM mus cles from the callipyge lambs were heavier (P < 0.05) than those from norma l lambs; however, the SS did not differ (P > 0.05) between phenotypes at 7, 20, or 52 kg. From 20 to 69 kg LW, the LM and SM weights were 42 and 49% h eavier (P < 0.05) for callipyge than for normal lambs. Calpastatin activity of the callipyge LM was greater (P < 0.05) than that of normal LM at 36, 5 2, and 69 kg. In the callipyge LM, CA was similar (P > 0.05) at 20, 36, and 52 kg LW and did not differ (P > 0.05) from 7-kg or 69-kg values. Calpasta tin activity declined (P < 0.05) across the growth curve for the SM and SS, but values were higher (P < 0.05) in the SM: in callipyge than in normal l ambs. Shear force values of the LM were lower (P < 0.05) for normal lambs a t 36, 52, and 69 kg LW than for callipyge lambs. In the SM and SS, WBS valu es decreased (P < 0.05) across the growth curve, but values were higher (P < 0.05) for callipyge lambs in the SM only. These data indicate that the se lective muscular hypertrophy of the callipyge phenotype develops during the postnatal growth period between 7 and 20 kg LW (19 and 100 d of age). Long issimus and semimembranosus muscles in the callipyge lambs were over 40% he avier from 20 to 69 kg LW; however, they also had higher levels of calpasta tin activity and Warner-Bratzler shear force during this time period, indic ating the need for postmortem tenderization treatments to improve palatabil ity.