PSXIV-26 - Live animal longissimus thoracis mitochondrial capacities at 10, 13, and 18 months of age are related to meat quality in Angus and Brahman steers

Abstract: Mitochondrial abundance and efficiency correlate with meat color, but relationships between live animal mitochondria and other markers of beef quality remain largely unknown. To test the hypothesis that live animal skeletal muscle mitochondrial markers would be correlated with post-harvest hot carcass weight, ribeye area, calculated yield grade, backfat thickness, and marbling, samples were collected from the longissimus thoracis of Brahman and Angus steers at 10 mo (25 Angus, 23 Brahman), 13 mo (35 Angus, 33 Brahman), and 18 mo (35 Angus, 33 Brahman) of age. Mitochondrial volume density and function were quantified by citrate synthase (CS) and cytochrome c oxidase activities, respectively. Mitochondrial oxidative phosphorylation (P) and electron transfer (E) capacities were determined via high-resolution respirometry. Relationships between mitochondrial variables and carcass quality were determined using PROC CORR in SAS (v9.4). Within Angus at 10 mo, integrative (per mg tissue) complex I-supported P (P_CI), maximal P (P_CI+II), maximal E (E_CI+II), and E supported by complex II (E_CII) were positively correlated with hot carcass weight (P ≤ 0.05). Also within 10 mo Angus, integrative P<sub>CI and flux control ratio (FCR) for P<sub>CI were positively correlated with backfat thickness (P ≤ 0.03). Within 10 mo Brahman, integrative P<sub>CI was positively correlated with ribeye area (P = 0.04). Within 13 mo Brahman, integrative mitochondrial proton LEAK was positively correlated with hot carcass weight (P = 0.02) and intrinsic (relative to CS activity) LEAK, P<sub>CI, and E_CI+II were positively correlated with marbling (P ≤ 0.05). Conversely, CS activity was negatively correlated with marbling in 13 mo Brahman (P = 0.05). Integrative, FCR, and intrinsic LEAK were negatively correlated with ribeye area (P ≤ 0.05) but positively correlated with calculated yield grade in 13 mo Angus (P ≤ 0.03). However, at 18 mo, integrative, FCR, and intrinsic LEAK were positively correlated with ribeye area (P ≤ 0.008) but negatively correlated with calculated yield grade (P ≤ 0.01) in Angus steers. Furthermore, integrative and intrinsic P<sub>CI+II, E_CI+II, and E_CII were positively correlated with marbling in 18 mo Angus (P ≤ 0.04). Within 18 mo Brahman, CS activity was positively correlated with ribeye area (P = 0.006). Cytochrome c oxidase activity was not correlated with any markers of meat quality. These results suggest that mitochondrial capacity for energy production in Angus and Brahman steers at different life and production stages may dictate potential for skeletal muscle growth and lipid metabolism leading to differences in beef quality at slaughter. This project was supported by USDA NIFA Award #2021-67015-33392.