Hypothermia is directly linked to metabolism; however, it is still unknown how the overall metabolism is altered by oral administration of hypothermic agent, l-citrulline (l-Cit). The present study aimed to determine the characteristics of liver metabolites of chicks orally administered l-Cit to provide a greater understanding of its metabolism. Capillary electrophoresis–time-of-flight mass spectrometry (CE-TOFMS) and liquid chromatography–time-of-flight mass spectrometry (LC-TOFMS) were conducted on liver samples after oral administration of l-Cit. A total of 361 liver metabolites were identified. Although a small number of samples were used for each group, a principal component analysis and heatmap patterns confirmed that the composition of metabolites could be segregated from each other. Of the 361 compounds detected in the liver, 41 compounds, including amino acids related to the Cit-arginine (Arg) cycle, argininosuccinic acid, Arg, ornithine, and Cit, as well as gamma aminobutyric acid, glycine, histidine, and nicotinamide adenine dinucleotide were abundant in l-Cit-treated livers. In contrast, 24 compounds containing fatty acids, amino acids, and cyclic adenosine monophosphate were lower in the l-Cit group. These data imply that the active Cit-Arg cycle, TCA cycle metabolism, and a low activity in fatty acid metabolism occur in l-Cit-treated broiler chicks.
