Effects of high ambient temperature on plasma metabolomic profiles in chicks.

Exposure to high ambient temperature is detrimental to the poultry industry. To understand the influence from a metabolic perspective, we investigated the effects of exposure to high ambient temperature on plasma low-molecular-weight metabolite levels in chicks using gas chromatography/mass spectrometry-based non-targeted metabolomic analysis. Heat exposure for 4 days suppressed growth and food intake. Of the 92 metabolites identified, the levels of 29 decreased, whereas the levels of nine increased. We performed an enrichment analysis on the identified metabolites and found 35 candidates for metabolic processes affected by heat exposure. Among them, the sulfur amino acid metabolic pathway was clearly detected and the levels of the following related metabolites were decreased: cystathionine, cysteine, cystine, homocysteine and hypotaurine. Changes in the kynurenine pathway in tryptophan metabolism, which is linked to the immune system and oxidative stress, were also observed: kynurenine and quinolinic acid levels increased, whereas nicotinamide levels decreased. These results suggest the possible involvement of various metabolic processes in heat-exposed chicks. Some of these metabolites would be important to understand the mechanism of biological responses to high ambient temperature in chicks.