277 Live Animal Mitochondrial Markers During the Feedlot Phase are Related to Meat Quality in Angus but not Brahman Steers

Mitochondrial activity correlates with meat product quality post-harvest but little is known about the relationships between live animal mitochondria and product quality at slaughter. To test the hypothesis that live animal skeletal muscle mitochondrial markers would be correlated with longissimus Warner-Bratzler shear force (WBSF) post-harvest, longissimus thoracis (LT) and trapezius (TRAP) samples were collected from Brahman and Angus steers (n = 36 per breed) during the grazing growth phase (GP) and after 120 days on feed (FP). Samples were analyzed for mitochondrial enzyme activities via colorimetry and for oxidative phosphorylation (P) and electron transfer (E) capacities via high-resolution respirometry. Relationships between mitochondrial variables and WBSF were determined using PROC CORR in SAS (v9.4). Within Angus in GP, LT mitochondrial volume density as measured by citrate synthase activity (CS) was positively correlated with WBSF (P=0.009). In FP, Angus LT intrinsic (relative to CS) P with complex I (PCI) and maximal E with complexes I and II (ECI+II) were positively correlated with WBSF (P≤0.05), while the contribution of maximal P with complexes I and II (PCI+II) to maximal E (flux control ratio, FCRPCI+II) was negatively correlated with WBSF (P=0.03). Also in FP, Angus TRAP integrative (relative to mg tissue) PCI, PCI+II, and ECI+II and FCRPCI were negatively correlated with WBSF (P≤0.02), while the FCR for electron transfer through complex II only (FCRECII) was positively correlated with WBSF (P=0.007). In Brahman, no mitochondrial markers correlated with WBSF during either GP or FP. Post-harvest meat tenderness is related to live animal skeletal muscle mitochondrial markers when evaluated close to slaughter in Angus but not in Brahman steers.