Effect of Glutamine on the Growth Performance, Oxidative Stress, and Nrf2/p38 MAPK Expression in the Livers of Heat-Stressed Broilers

SIMPLE SUMMARY: Dietary glutamine (Gln) supplementation can significantly alleviate the negative effects on product performance and antioxidant capacity in chickens exposed to hot environments. However, the antioxidant effect of Gln on the liver in heat-stressed broilers and its mechanism of action are rarely reported. The aim of the present study was to investigate the effect of glutamine on the growth performance, oxidative stress, and Nrf2/p38 MAPK single pathway in the livers of broilers exposed to high temperature conditions. Results showed that high temperature conditions decreased growth performance and induced oxidative stress in broiler livers. Dietary Gln improved the growth performance, antioxidant enzyme, Nrf2, and p38 MAPK expression in the livers of heat-stressed broilers. In conclusion, this study suggested that Gln can improve the liver’s response to oxidative stress by increasing the Nrf2/p38 MAPK expression. Gln can be used as a feed additive for broiler production in high-temperature environments such as during the summer season. ABSTRACT: The purpose of this work was to study the effects of glutamine (Gln) on the growth performance, oxidative stress, Nrf2, and p38 MAPK pathway in the livers of heat-stressed broilers. In total, 300 broilers were divided into five groups, including a normal temperature (NT, without dietary Gln) group and four cyclic high temperature groups (HT, GHT1, GHT2, and GHT3) fed with 0%, 0.5%, 1.0%, and 1.5% Gln, respectively. High temperature conditions increased (p < 0.05) liver malonaldehyde (MDA) concentration, but decreased (p < 0.05), body weight gain (BWG), feed intake (FI), liver superoxide dismutase (SOD), total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST), and glutathione (GSH) levels in broilers. Nrf2 and p38 MAPK protein and mRNA expression levels were lower (p < 0.05) in the NT group than that in the HT group. However, dietary 1.5% Gln decreased (p < 0.05) liver MDA concentration, but increased (p < 0.05) BWG, FI, liver SOD, T-AOC, GSH-Px, GST, and GSH levels in heat-stressed broilers. Nrf2 and p38 MAPK protein and mRNA expression levels were higher (p < 0.05) in the GHT3 group than that in the HT group. In summary, Gln improved oxidative damage through the activation of Nrf2 and p38 MAPK expression in the livers of heat-stressed broilers.