**5. Conclusions**

A cyclic HT environment altered nucleic acid metabolism and increased lipid peroxidation levels in the plasma and breast muscle of broiler chickens. Feeding the pyrimidine precursor orotic acid to the chickens altered the plasma concentrations of metabolites mainly related to pyrimidine metabolism and β-alanine metabolism, and ameliorated the increases in lipid peroxidation levels caused by rearing the broiler chickens under HT conditions.

**Supplementary Materials:** The following is available online at http://www.mdpi.com/2218-1989/10/5/189/s1, Table S1. E ffects of a cyclic high ambient temperature and feeding orotic acid on the muscle yields of broiler chickens. Table S2. Metabolites identified in the plasma of broiler chickens reared under either thermoneutral or high ambient temperature (HT) conditions, and fed either a control or orotic acid-supplemented diet.

**Author Contributions:** Conceptualization, S.S., K.N., S.F., A.O., and D.I.; methodology, D.I. and S.T.; software, S.T. and D.I.; validation, S.S. and S.T.; formal analysis, S.S. and K.N; investigation, S.S. and K.N.; resources, S.F; original draft preparation, S.S. and K.N; manuscript review and editing, S.S., S.T., S.F., A.O., and D.I.; supervision, A.O.; project administration, D.I. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the Furukawa Research Office Co., Ltd., and a Grant-in-Aid for Scientific Research (C) (No. 19K06357) from The Japan Society for the Promotion of Science (JSPS) to D. Ijiri., Kagoshima University, and received no specific grants from any funding agency in the public, commercial, or not-for-profit sectors.

**Conflicts of Interest:** The authors declare no conflict of interest.
