Dietary glycine supplementation prevents heat stress-induced impairment of antioxidant status and intestinal barrier function in broilers

Abstract

This study tested the hypothesis that glycine improves intestinal barrier function through regulating oxidative stress in broilers exposed to heat stress. A total of 300 twenty-one-day-old female Arbor Acres broilers (600 ± 2.5g) was randomly allocated to 5 treatments (6 replicate of 10 birds each). The 5 treatments were as follows: the control group (CON) was kept under thermoneutral condition (24 ± 1°C) and was fed a basal diet. Broilers fed a basal diet and reared under high ambient temperature (HT) were considered as the HT group (34 ± 1°C for 8 h/d). Broilers fed a basal diet supplemented with 0.5%, 1.0%, and 2.0% glycine and exposed to HT were regarded as the HT + glycine treatments. The results exhibited that heat stress reduced growth performance, serum total antioxidant capacity (T-AOC), and glutathione (GSH) concentration (P < 0.05); increased activity of serum catalase (CAT) and the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) (P < 0.05). HT exposure led to downregulating the mRNA expression of NAD(P)H quinone dehydrogenase 1 (NQO1), Occludin, and zonula occludens-1 (ZO-1) (P < 0.05); enhanced the mRNA levels of Kelch-like ECH-associated protein 1 (Keap1), CAT, glutathione synthetase (GSS), and glutamate-cysteine ligase modifier subunit (GCLM) (P < 0.05); impaired the intestinal morphology (P < 0.05); and altered the diversity and community of gut microbiota (P < 0.05). The final body weight (FBW), ADFI, ADG, and gain-to-feed ratio (G: F) increased linearly or quadratically, and the antioxidant capacity was improved (P < 0.05) with glycine supplementation. Glycine treatment increased the villus height (VH), and villus height to crypt depth ratio (V/C) of the duodenum linearly or quadratically, and linearly increased the VH of jejunum and ileum. The mRNA expression of Occludin, and ZO-1 were increased linearly in the ileum mucosa of broilers subjected to HT. Collectively, these results demonstrated that glycine supplementation alleviates heat stress-induced dysfunction of antioxidant status and intestinal barrier in broilers.

Keywords: Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2 signaling pathway; antioxidant status; glycine; heat stress; intestinal barrier function.

Figure 1

Summary of the microbiomes in the ileal mucosa. (A) Alpha diversity indexes (ACE, Chao1, Simpson, Shannon). (B) Principal co-ordinates analysis (PCoA) and PERMANOVA test plot. (C) Relative abundance of bacterial composition at phylum and genus levels. CON: basal diet and raised under thermoneutral conditions; HT: basal diet and raised under cyclic high-temperature conditions; HTG: basal diet supplemented with 2.0% glycine under cyclic high-temperature conditions (n = 6). *Significant difference between CON and HT, HT and HTG by t test (P < 0.05).

Figure 2

Summary of the microbiomes in the ileal mucosa. (A) LEfSe analysis at phylum level (LDA score >2.0). (B) Correlation between top 15 microbiota at phylum level and mRNA expression of Keap1/Nrf2-related genes, tight junction protein. Red indicates a positive correlation, whereas blue represents a negative correlation. Significance is presented as * (P < 0.05). CON: basal diet and raised under thermoneutral conditions; HT: basal diet and raised under cyclic high-temperature conditions; HTG: basal diet supplemented with 2.0% glycine under cyclic high-temperature conditions (n = 6).