Relationships between residual feed intake (RFI) and other performance variables were determined using 54 purebred Angus steers. Individual feed intake and BW gain were recorded during a 70-d post-weaning period to calculate RFI. After the 70-d post-weaning test, steers were fed a finishing ration to a similar fat thickness (FT), transported to a commercial facility, and slaughtered. A subsample of carcasses (n = 32) was selected to examine the relationships among RFI, meat quality, and palatability. Steers were categorized into high (> 0.5 SD above the mean; n = 16), medium (mid; +/- 0.5 SD from the mean; n = 21), and low (< 0.5 SD below the mean; n = 17) RFI groups. No differences were detected in ADG, initial BW, and d 71 BW among the high, mid, and low RFI steers. Steers from the high RFI group had a greater DMI (P = 0.004) and feed conversion ratio (FCR; DMI:ADG; P = 0.002) compared with the low RFI steers. Residual feed intake was positively correlated with DMI (r = 0.54; P = 0.003) and FCR (r = 0.42; P = 0.002), but not with initial BW, d 71 BW, d 71 ultrasound FT, initial ultrasound LM area, d 71 ultrasound LM area, or ADG. The FCR was positively correlated with initial BW (r = 0.46; P = 0.0005), d 71 BW (r = 0.34; P = 0.01), and DMI (r = 0.40; P = 0.003) and was negatively correlated with ADG (r = -0.65; P = 0.001). There were no differences among RFI groups for HCW, LM area, FT, KPH, USDA yield grade, marbling score, or quality grade. Reflectance color b* scores of steaks from high RFI steers were greater (P = 0.02) than those from low RFI steers. There was no difference between high and low RFI groups for LM calpastatin activity. Warner-Bratzler shear force and sensory panel tenderness and flavor scores of steaks were similar across RFI groups. Steaks from high RFI steers had lower (P = 0.04) off-flavor scores than those from low RFI steers. Cook loss percentages were greater (P = 0.005) for steaks from low RFI steers than for those from mid RFI steers. These data support current views that RFI is independent of ADG, but is correlated with DMI and FCR. Importantly, the data also support the hypothesis that there is no relationship between RFI and beef quality in purebred Angus steers.

The longissimus muscles (LM) from 12 lambs (eight = callipyge [CLPG] and four = normal [NML]; 48 kg) were used to 1) assess the effect of freezing with or without prior immersion in liquid nitrogen on calpastatin activity (CA) and on Warner-Bratzler shear force (WBS) in CLPG, 2) determine the freezing time required to reduce CA and WBS of CLPG to that of NML, and 3) compare sensory panel ratings for CLPG that is aged fresh to CLPG that is aged after freezing. At 24 h postmortem, chops (.64 and 2.54 cm) were removed from each CLPG LM and randomly assigned within side to one of six freezing times (0, 2, 4, 8, 20, and 42 d). Left-side chops were vacuum-packaged and frozen at -20 degrees C for the assigned time (FROZEN) and right-side chops were treated similarly, except that they were frozen in liquid nitrogen first (FLASH). After freezing for the assigned time, the.64-cm chop was immediately assayed for CA, and 2.54-cm chop was thawed, aged at 2 degrees C for 14 d, and refrozen for subsequent WBS measurement. Chops (.64 and 2.54 cm) were also removed from the longissimus of NML lamb carcasses. The d-0 CLPG and NML chops (2.54 cm) were vacuum-packaged, aged at 2 degrees C for 14 d, and frozen for subsequent WBS measurement. Calpastatin activity did not differ between freezing treatments (P =.99) or with the freezing treatment x freezing time interaction (P =.80). Freezing reduced (P =.01) CA in CLPG by 44% from d 0 to d 42. Calpastatin activity for CLPG was similar (P >.05) to that of NML lamb after freezing for 8, 20, or 42 d. Freezing at -20 degrees C for 42 d and then aging for 14 d reduced(P =.01) WBS in CLPG by 44% from d-0 values. Shear force values for CLPG-FROZEN were similar (P >.05) to NML after 8, 20, or 42 d of freezing. Sensory panel tenderness scores were higher (P <.05) for CLPG aged after freezing 42 d than for those aged fresh. Juiciness and flavor ratings did not differ (P >.05) between CLPG aged fresh or after freezing. Freezing for at least 8 d before aging seems to be a viable method for increasing the tenderness of CLPG LM without reducing juiciness or flavor ratings.

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 CaCl2 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.