LAUSR

This study applied a chemical isotope labeling/liquid chromatography mass spectrometry-based metabolomics technique to determine differences in plasma metabolites containing amine/phenol and carbonyl chemical groups in beef steers with divergent average daily gain (ADG). Thirty-eight Angus crossbred beef steers (21 d post-weaning; 210 ± 12 kg of BW) from a single source were housed in individual slatted floor pens and were fed the same total mixed ration (CP = 14.5% and NEg = 1.10 Mcal/kg) ad libitum for 42 d with free access to water. After 42 days of feeding, the steers were divided into two groups of lowest ADG (LF: n = 8) and highest (HF: n = 8) ADG. Blood samples were taken from both LF and HF steers and were immediately centrifuged to harvest the plasma. The average daily DM intake of the steers in LF and HF were 6.08 kg ± 0.57 and 6.04 kg ± 0.42, respectively, and was similar between the two groups (P = 0.72). The ADG of LF (0.99 kg ± 0.23) was lower (P = 0.01) than that of HF (1.63 kg ± 0.20). A total number of 42 carbonyl-containing metabolites and 229 amine/phenol-containing metabolites were identified in the plasma samples of both groups. No alteration in carbonyl-metabolome was detected. Ten metabolites including 4,6-dihydroxyquinoline, prolyl-valine, prolyl-leucine, prolyl-isoleucine, L-formylkynurenine, pyrocatechol, and histidine were greater in HF steers whereas 8 metabolites including arginine, phenylalanine, guanidoacetic acid, and aspartyl-threonine were greater in LF steers. This study demonstrated that beef steers with divergent ADG had altered plasma amine/phenol metabolome. Notably, plasma concentrations of dipeptides containing branched chain amino acid residues (prolyl-valine, prolyl-leucine, prolyl-isoleucine) and metabolites with anti-inflammatory and reactive oxygen-scavenging properties (4,6-dihydroxyquinoline and L-formylkynurenine) were greater in steers with high ADG.