Effect of chronic cyclic heat stress on the intestinal morphology,oxidative status and cecal bacterial communities in broilers

The objective of this study was to examine the effects of chronic cyclic heat stress (HS) on the intestinal morphology, oxidative stress and cecal bacterial communities of broilers. One-day-old Arbor Acres (AA) male broilers (n = 100) were acclimated for 3 weeks and then randomly allocated into two groups, normal control (NC) group (22 ± 1 °C, 24 h/day) and HS group (32 ± 1 °C, 10 h/day lasted for 2 weeks). At 35 d of age, intestinal segments (duodenum, jejunum and ileum) and cecal digesta were collected for detection. HS affected intestinal morphology, inducing epithelial cell abscission, inflammatory cell infiltration, and lamina propria edema. Compared with the NC group, HS significantly decreased (P < 0.01) villus height (VH) and the VH-to-crypt depth (CD) ratio (VCR), increased (P < 0.05) CD in the duodenum and ileum, but had no effect on the VH in the jejunum. Moreover, HS induced oxidative stress with antioxidant enzymes activity decreasing (P < 0.05) while malondialdehyde (MDA) content increasing (P < 0.05) in small intestine. Pearson's correlation analysis indicated that MDA content was negatively correlated with VH (P < 0.05). The result of 16S rRNA sequencing showed that HS exposure impacted cecal microbiota alpha diversity (phylogenetic diversity whole-tree index) and beta diversity. Based on principal coordinate analysis (PCoA) plots for weighted UniFrac metrics and unweighted pair group method with arithmetic mean (UPGMA), there were 8 discriminative features at the genus level (linear discriminant analysis score > 2). Parabacteroides, Saccharimonas, Romboutsia and Weissella were reduced, while Anaerofustis, Pseudonocardia, Rikenella and Tyzzerella were enriched in heat-stressed broilers. Collectively, these results indicated that chronic cyclic HS induced oxidative stress that caused damage to intestinal villus-crypt structures, and then altered the cecal microflora profile.