Influence of feed efficiency classification and growing and finishing diet type on meat tenderness attributes of beef steers

Enhancing feed efficiency (FE) in cattle continues to be an important goal in the beef industry. Previous research suggests improving FE may alter calpain system activity, potentially having negative effects on meat tenderness. The objective of this study was to assess the potential influence of beef cattle FE on postmortem meat tenderness. During the growing phase, 181 crossbred steers were fed for 76 d at the University of Missouri on a whole shell corn-based diet (MU-Corn; n = 90) or a roughage-based diet (MU-Rough; n = 91). Within diet, steers were classified for FE based on residual feed intake (RFI) calculations. Within each growing phase diet, the 12 most feed efficient (HFE; average RFI -3.33 +/- 0.77) and 12 least feed efficient (LFE; average RFI 2.90 +/- 0.94) steers (48 steers total) were selected and shipped to Iowa State University for the finishing phase. Steers were fed in pens with GrowSafe bunks and equally assigned to a cracked corn-based finishing diet (ISU-Corn) or a byproduct-based finishing diet (ISU-Byp) for the 87-d finishing phase. After a 24-h chill, rib sections were collected from all carcasses and aged for 2 or 14 d prior to analysis of calpastatin activity and calpain 1 autolysis (d 2), troponin-T degradation (d 2 and 14), proximate composition (d 2), and Warner-Bratzler shear force (WBSF; d 14). Data were analyzed as a 2 x 2 x 2 factorial, with steer or steak as the experimental unit (n = 6 per treatment combination). There were no 3-or 2-way interactions (P >= 0.12) noted for any data, with the exception of steak lipid content, which tended (P = 0.08) to be affected by FE x Iowa State University diet. Steaks from LFE steers had greater lipid content compared with steaks from HFE steers within ISU-Byp, with no differences due to FE within ISU-Corn. Growing diet did not affect calpastatin activity, calpain 1 autolysis, or troponin T degradation (P >= 0.12); however, MU-Rough had greater WBSF than MU-Corn (P = 0.05). Day-2 calpastatin activity tended (P = 0.10) to be greater in steaks from HFE vs. LFE steers, although no differences due to FE classification were observed for calpain 1 protein, troponin-T degradation, or WBSF (P >= 0.13). Finishing diet did not affect calpastatin activity, calpain 1 autolysis, d-2 troponin-T degradation, or WBSF (P >= 0.24); however, d-14 troponin-T degradation was greater in ISU-Corn than in ISU-Byp (P = 0.005). In this study, using phenotypic extremes for FE revealed a tendency for greater calpastatin activity only in highly feed-efficient steers; however, these data indicate that high-fiber diets may negatively impact meat tenderness, and further work is needed to clarify the influence of diet type on parameters of meat tenderness.