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Post-mortem proteolysis and meat tenderness in crossbred steers identified as lowly or highly feed efficient
ABSTRACT: The objective of this study was to assess effects of beef cattle feed efficiency (FE) on post-mortem meat tenderness. Crossbred steers were grown at the University of Missouri (76 d) on a whole-shell corn (MUCorn, n = 89) or roughage-based diet (MURough, n = 90), phenotypically classified for FE based on residual feed intake (RFI) calculations and finished at Iowa State University (ISU). Within each growing phase (GP) diet, the 12 greatest (HFE; average RFI -3.33 ± .77,SE) and 12 least (LFE; average RFI 2.90 ± .94) efficient steers (48 steers total) were assigned to GrowSafe pens and transitioned to corn (ISUCorn) or byproduct-based diet (ISUByp; 87d) for the finishing phase (FP). Optaflexx was fed for 28-d prior to harvest. Rib sections were collected from the 48 steers, and aged for 2 or 14-days for further analysis of calpastatin (d2), troponin-T (d2, d14), and WBSF (d14). Data were analyzed using PROC MIXED of SAS with fixed effects of MU diet, ISU diet, FE classification, and the interactions; significance was determined at P ≤ 0.05. Dressing percent and ribeye area were greater in LFE steers than HFE steers (P ≤ 0.04), and ribeye area was increased in ISUCorn vs. ISUByp steers (P = 0.01). There was a tendency for an ISU diet x FE effect on steak lipid content (P = 0.08) and marbling score (P = 0.03) driven by greater lipid content in steaks from LFE steers vs. HFE steers within ISUByp, but no differences were detected due to FE classification within ISUCorn. Moisture and protein content of the steaks were not affected by diet or FE (P ≥ 0.12). Minolta objective color scores and percent cook loss measured on steaks aged 14d revealed no differences due to diet or FE (P ≥ 0.21). No interaction between diets and FE classification (P ≥ 0.19) were observed for Warner-Bratzler shear force (WBSF), calpastatin activity, or d2 or d14 troponin-t degradation. However, MURough steers had greater WBSF than MUCorn steers (P = 0.05). Day 2 calpastatin activity tended (P = 0.10) to be greater in HFE steers than LFE steers. No differences were observed in d2 troponin-t degradation (P ≥ 0.12); however, d14 troponin-t was greater in ISUCorn vs. ISUByp steers (P = 0.005). These data suggest that diet type and feed efficiency classification may independently affect meat tenderness.
Keywords: cattle, feed efficiency, meat tenderness