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外源胆汁酸对热应激肉鸡抗氧化状态和肠道微生物群的影响

The effect of exogenous bile acids on antioxidant status and gut microbiota in heat-stressed broiler chickens

作者：Chang Yin, Bing Xia, Shanlong Tang, Aizhi Cao, Lei Liu, Ruqing Zhong, Liang Chen, Hongfu Zhang.

发布期刊：Frontiers in nutrition. 2021 Nov 24;8:747136.

胆汁酸对脂质吸收至关重要，然而其在维持或调节系统代谢中的同样不容忽视。热应激( heat stress，HS )对肉鸡生长性能、脂质代谢和抗氧化状态的负面影响已有报道，但热应激是否影响肉鸡胆汁酸组成尚不清楚。因此，本试验旨在研究肉鸡在HS环境中调节作用，以及日粮添加胆汁酸是否有利于肉鸡热应激状况的改善。选取平均体重接近的AA肉鸡216羽，于21-42日龄分别进行常温、热应激( 32°C )和HS-胆汁酸 (日粮中添加200 mg / kg 胆汁酸)处理。结果显示，相对于HS组，HS-胆汁酸组平均日增重显著增加(P<0.05)，血清和肝脏中谷胱甘肽过氧化物酶活性恢复至正常范围(P< 0.05)。HS导致回肠中初级胆汁酸 (P=0.084, 38.46 %)和牛磺结合型胆汁酸 (33.49%)的含量下降。同时，肝脏和盲肠中的次级胆汁酸分别降低了36.88和39.45 %。值得注意的是，血清(3倍, P = 0.0003)和回肠(24.89倍, P < 0.0001) 中的次级胆汁酸水平显著增加。其中，TUDCA水平极显著增加(P<0.01)。此外，胆汁酸的添加显著提高了肝脏中TUDCA (P=0.0154)和THDCA (P=0.0003)的水平，回肠中TDCA (P=0.0307)、TLCA (P = 0.0453)、HDCA (P =0.0018)和THDCA (P =0.0002)的水平也有所提高。通过HE染色观察形态，胆汁酸降低了热应激下肉鸡回肠的隐窝深度(P=0.0431)，绒毛高度与隐窝深度的比值有升高的趋势(P= 0.0539)。RT - PCR结果显示，日粮添加胆汁酸上调了回肠FXR (P =0.0369)、ASBT (P = 0.0154)和Keap-1(P =0.0104)基因的表达，下调了回肠iNOS (P=0.0399)基因的表达。此外，16S rRNA基因测序和相关代谢网络分析，揭示了热应激导致的肉鸡肠道微生物群和胆汁酸代谢物的变化可能影响其对热应激的抗性。因此，在高温环境下补充胆汁酸可使肉鸡获益，可作为一种新的抗热应激营养策略。

Bile acids are critical for lipid absorption, however, their new roles in maintaining or regulating systemic metabolism are irreplaceable. The negative impacts of heat stress (HS) on growth performance, lipid metabolism, and antioxidant status have been reported, but it remains unknown whether the bile acids (BA) composition of broiler chickens can be affected by HS. Therefore, this study aimed to investigate the modulating effects of the environment (HS) and whether dietary BA supplementation can benefit heat-stressed broiler chickens. A total of 216 Arbor Acres broilers were selected with a bodyweight approach average and treated with thermal neutral (TN), HS (32°C), or HS-BA (200 mg/kg BA supplementation) from 21 to 42 days. The results showed that an increase in average daily gain (P < 0.05) while GSH-Px activities (P < 0.05) in both serum and liver were restored to the normal range were observed in the HS-BA group. HS caused a drop in the primary BA (P = 0.084, 38.46%) and Tauro-conjugated BA (33.49%) in the ileum, meanwhile, the secondary BA in the liver and cecum were lower by 36.88 and 39.45% respectively. Notably, results were consistent that SBA levels were significantly increased in the serum (3-fold, P = 0.0003) and the ileum (24.89-fold, P < 0.0001). Among them, TUDCA levels (P < 0.01) were included. Besides, BA supplementation indeed increased significantly TUDCA (P = 0.0154) and THDCA (P = 0.0003) levels in the liver, while ileal TDCA (P = 0.0307), TLCA (P = 0.0453), HDCA (P = 0.0018), and THDCA (P = 0.0002) levels were also increased. Intestinal morphology of ileum was observed by hematoxylin and eosin (H&E) staining, birds fed with BA supplementation reduced (P = 0.0431) crypt depth, and the ratio of villous height to crypt depth trended higher (P = 0.0539) under the heat exposure. Quantitative RT-PCR showed that dietary supplementation with BA resulted in upregulation of FXR (P = 0.0369), ASBT (P = 0.0154), and Keap-1 (P = 0.0104) while downregulation of iNOS (P = 0.0399) expression in ileum. Moreover, 16S rRNA gene sequencing analysis and relevance networks revealed that HS-derived changes in gut microbiota and BA metabolites of broilers may affect their resistance to HS. Thus, BA supplementation can benefit broiler chickens during high ambient temperatures, serving as a new nutritional strategy against heat stress.

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