Liver Metabolomics Analysis Associated with Feed Efficiency on Steers

The liver represents a metabolic crossroad regulating and modulating nutrients available from digestive tract absorption to the peripheral tissues. To identify potential differences in liver function that lead to differences in feed efficiency, liver metabolomic analysis was conducted using ultra-performance liquid chromatography, time-of-flight mass spectrometry (MS). Individual feed intake and BW gain was measured on 144 crossbred steers for 105 d on a high concentrate diet. Eight steers with the greatest ADG and 8 steers with the least ADG within 0.32 SD of the mean DMI were selected for the study. The DMI did not differ between ADG groups (10.10 ± 0.05 kg/d; P=0.41); however, ADG was greater (P < 0.01) in the greatest-ADG group (1.96 ± 0.02 kg/d) than in the least-ADG group (1.57 ± 0.02 kg/d). Liver was collected at slaughter. Metabolite identification was obtained through a mass-based bovine database search. Verification of the identities of selected metabolites was conducted by comparing MS/MS fragmentation patterns with those from authentic compounds. Principal component analysis, fold changes and t-tests on rumen fluid metabolic profile identified 96 metabolites (P < 0.05) that segregated with ADG group. These metabolites were primarily involved in taurine and hypotaurine (impact-value 0.75; P = 0.10) and glycerophospholipids metabolism (impact-value 0.34; P < 0.01), which were up-regulated in the highest-ADG as compared to lowest-ADG group. Conversly, glutathione metabolism (impact-value 0.36; P = 0.01) was up-regulated in the least-ADG vs. greatest-ADG group. Hepatic levels of 5 metabolites associated with ADG group were quantified and screened by receiver operating curve (ROC) analysis to test their efficacy as biomarkers for ADG. Hepatic concentration of L-glutathione decreased (P < 0.01) in the greatest-ADG (4.56 µg/mL) vs. least-ADG (8.21 µg/mL) animals while taurocholic acid increased (P = 0.06) in the greatest-ADG (5.53 µg/mL) vs. least-ADG (2.74 µg/mL) animals. However, hepatic concentration of L-homocysteine, L-methionine and L-cysteine was not affected by ADG (P > 0.10). The combination of L-homocysteine and L-glutathione ratio was a good predictor of ADG; area under the curve from the ROC analysis was 0.934 with a 95% CI of 0.78-1.0 representing 87.5% of sensitivity and 87.5% of specificity. From these results, we deduce that the hepatic metabolic profile provides new insight into the physiological mechanisms of cattle feed efficiency. USDA is an equal opportunity provider and employer.