Abstract
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.
Highlights
According to the Food and Agriculture Organization (FAO), chicken meat accounted for 36.5% of all meat produced worldwide, owing to its rich nutrition, low cost, high-quality protein, low cholesterol, and low fat [1]
After the 5-day adaptation in the environmental control cabins, the temperature of heat stress (HS) and HS-Bile acids (BA) groups was increased to 32◦C in 2 h on d21, the remaining cabins were maintained at 23◦C, and the humidity in all cabins was maintained at 60 ± 5% until d42
Our results showed that heat stress up-regulated the expression of ileal kelch-like ECH-associated protein 1, and regardless of thermal neutral group (TN) or HS, and exogenous BA up-regulated the expression of keap-1 in ileal
Summary
According to the Food and Agriculture Organization (FAO), chicken meat accounted for 36.5% of all meat produced worldwide (equivalent 117.2 million metric tons), owing to its rich nutrition, low cost, high-quality protein, low cholesterol, and low fat [1]. Our previous study suggested that chronic heat stress caused a reduction in Tauro-conjugated bile acids (TCBA) synthesis, conjugation, and uptake transport in pigs, which was independent of reduced feed intake [6]. Bile acids (BA) play important roles in lipid and fat-soluble substances digestion, antioxidant status, and lipid metabolism, etc. The primary BA is synthesized from cholesterol in the liver, secreted into the intestine lumen primarily as the amino acid conjugates. Our previous study suggested that bile acids explained 37.1% of variations in the luminal microbial composition in growing pigs [11]. Gut microbiota can deconjugate the glycine and taurine from conjugated bile acids to yield deconjugated bile acids, which is a critical step in microbial bile acid metabolism. Our and other previous studies have reported that the dysbiosis of the gut microbiota
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