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.

中文翻译：

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慢性循环热应激对肉鸡肠道形态、氧化状态和盲肠细菌群落的影响

本研究的目的是检查慢性循环热应激 (HS) 对肉鸡肠道形态、氧化应激和盲肠细菌群落的影响。一日龄Arbor Acres（AA）雄性肉鸡（n = 100）驯化3周，然后随机分为两组，正常对照组（NC）组（22±1°C，24小时/天）和HS组（32±1°C，10 小时/天，持续 2 周）。在 35 日龄时，收集肠段（十二指肠、空肠和回肠）和盲肠食糜进行检测。HS 影响肠道形态，诱​​导上皮细胞脱落、炎性细胞浸润和固有层水肿。与NC组相比，HS显着降低（P < 0.01）绒毛高度（VH）和VH与隐窝深度（CD）比（VCR），增加（P < 0.05）十二指肠和回肠的CD，但对空肠中的 VH 没有影响。此外，HS 诱导氧化应激，抗氧化酶活性降低（P < 0.05），而小肠中丙二醛（MDA）含量增加（P < 0.05）。Pearson 相关分析表明 MDA 含量与 VH 呈负相关（P < 0.05）。16S rRNA测序结果表明，HS暴露影响盲肠微生物群α多样性（系统发育多样性全树指数）和β多样性。基于加权 UniFrac 度量的主坐标分析 (PCoA) 图和具有算术平均值的未加权对组方法 (UPGMA)，在属水平上有 8 个判别特征（线性判别分析得分 > 2）。Parabacteroides、Saccharimonas、Romboutsia 和 Weissella 减少，而Anaerofustis、Pseudonocardia、Rikenella 和 Tyzzerella 富含热应激肉鸡。总的来说，这些结果表明，慢性循环 HS 诱导氧化应激，对肠绒毛隐窝结构造成损害，然后改变盲肠微生物群落分布。