**E** ff**ects of Cyclic High Ambient Temperature and Dietary Supplementation of Orotic Acid, a Pyrimidine Precursor, on Plasma and Muscle Metabolites in Broiler Chickens**

#### **Saki Shimamoto 1,2, Kiriko Nakamura 1, Shozo Tomonaga 3, Satoru Furukawa 4, Akira Ohtsuka 1 and Daichi Ijiri 1,\***


Received: 7 April 2020; Accepted: 10 May 2020; Published: 12 May 2020

**Abstract:** The aim of this study was to evaluate the e ffects of high ambient temperature (HT) and orotic acid supplementation on the plasma and muscle metabolomic profiles in broiler chickens. Thirty-two 14-day-old broiler chickens were divided into four treatment groups that were fed diets with or without 0.7% orotic acid under thermoneutral (25 ± 1 ◦C) or cyclic HT (35 ± 1 ◦C for 8 h/day) conditions for 2 weeks. The chickens exposed to HT had higher plasma malondialdehyde concentrations, suggesting an increase in lipid peroxidation, which is alleviated by orotic acid supplementation. The HT environment also a ffected the serine, glutamine, and tyrosine plasma concentrations, while orotic acid supplementation a ffected the aspartic acid, glutamic acid, and tyrosine plasma concentrations. Untargeted gas chromatography–triple quadrupole mass spectrometry (GC-MS/MS)-based metabolomics analysis identified that the HT a ffected the plasma levels of metabolites involved in purine metabolism, ammonia recycling, pyrimidine metabolism, homocysteine degradation, glutamate metabolism, urea cycle, β-alanine metabolism, glycine and serine metabolism, and aspartate metabolism, while orotic acid supplementation a ffected metabolites involved in pyrimidine metabolism, β-alanine metabolism, the malate–aspartate shuttle, and aspartate metabolism. Our results sugges<sup>t</sup> that cyclic HT a ffects various metabolic processes in broiler chickens, and that orotic acid supplementation ameliorates HT-induced increases in lipid peroxidation.

**Keywords:** chickens; heat stress; lipid peroxidation; metabolomics; orotic acid
