Application of Bile Acid in Livestock and Aquaculture

Bile acid is the terminal metabolite of cholesterol.

Chen Yuyan 1 Yuan 2 Yuan Li Jing 1# Yuan Liu Honghe 2 Yuan Fu Shi 1 3 Yuan Guxu 1 Yuan Liu Lu 4 Yuan Ma Ying 1 *

Yuan 1. Feed Research Institute of Chinese Academy of Agricultural Sciences Yuan Beijing 100081.2. Inspection and Testing Certification Center of Liaoning Province Yuan Liaoning Shenyang 110036.

3. Jiangxi Agricultural Technology Extension Center Yuan, Nanchang 330046, Jiangxi Province 4. Beijing Forestry University School of Economics and Management Yuan Beijing 100083 injustice

Bile acid is the terminal metabolite of cholesterol. Yuan has physiological functions such as regulating glucose and lipid metabolism, energy metabolism and immune response. Yuan, as a new feed additive, is widely used in animal breeding. In this paper, the physiological function of bile acid and its application in poultry Yao, pig Yao, aquatic products and other animal breeding are reviewed in order to provide reference for exogenous bile acid addition.

　　

 

[Key words] Bile acid, feed additive, animal husbandry, aquaculture

[Figure Classification Number] S816.7 [Document Identification Code] A

Bile acids are a type of C₂? 1 cholanic acid derivatives synthesized from cholesterol in liver parenchymal cells and stored in the gallbladder. They are the main metabolic pathway for cholesterol. It is usually combined with taurine or glycine in an amide bond under physiological conditions and is called a bile salt. Bile does not contain digestive enzymes, and bile salts are important substances that promote the digestion and absorption of lipids in the body. At the same time, bile acids can also be used as signal molecules to participate in the regulation of glucose and lipid metabolism, energy balance, immune response and other physiological functions (ðanic et al., 2018).

China's aquaculture industry is developing towards standardized, intelligent, intensive and green breeding mode. In this process, animals are facing their own imperfect development and various stresses in the external environment. In July 2014, bile acid was approved as a feed additive. Research and practice show that the appropriate dose of bile acid in animal feed can promote fat absorption, improve immunity and protect intestinal health, so bile acid is widely used in animal husbandry and aquaculture. This paper introduces the physiological function of bile acid, and summarizes its application effect and addition amount in poultry, pig, aquatic and other animal breeding, which has certain guiding significance for the scientific and rational use of bile acid in the breeding process.

1 Overview of Bile Acids

Bile acids, which are important components of bile, are usually derivatives of cholanoic acids with 24 carbon atoms, starting from cholesterol and involving catalytic reactions involving at least 17 different enzymes, are synthesized in the hepatocyte species via the classical (neutral) pathway and the alternative (acidic) pathway and stored in the gallbladder. Bile acids provide an important excretory pathway for cholesterol metabolism (Chiang,

2013). There are species differences in the production of non-12-OH bile acids by alternative pathways. Humans are dominated by chenodeoxycholic acid (CDCA), rodents are dominated by murine cholic acid (MCA), and pigs are dominated by porcine cholic acid (HCA). Studies have shown that porcine cholic acid can effectively regulate blood glucose homeostasis (Jia et al., 2021).

Bile acids are often conjugated with taurine or glycine to increase solubility and reduce cytotoxicity, and the formed bile salts are the major solid constituents in bile (Hofmann and Hagey,2008). Hydrophilic-OH,-COOH and lipophilic-CH/CH₂ are arranged on both sides of the steroid nucleus to make bile salts amphiphilic, which can emulsify fat into droplets, which is conducive to the decomposition of fat and the absorption of other fat-soluble nutrients. Studies in mammals have shown that primary bile acids enter the intestine and undergo hydrolysis, dehydroxylation and other modifications of the intestinal flora to produce secondary bile acids. Secondary bile acids can be absorbed from the distal intestine, becoming part of the circulating bile acid pool. Bile acids (both primary and secondary) reabsorbed from the gut undergo two to four enterohepatic cycles after each meal in humans, with approximately 95% of the bile acids being recycled and the remaining 5% being excreted in the feces (Xiang et al., 2021). In pigs, poultry, cattle, sheep and aquatic animals, the efficiency and frequency of bile acid circulation are not clear.

2 physiological function of bile acid

2.1 promoting the digestion and absorption of lipids, the flat steroidal structure of bile acids has a hydrophilic surface containing hydroxyl groups and a hydrophobic surface containing no substituents, which can be used as an emulsifier to reduce the surface tension of water and oil phases. The emulsified fat and fat-soluble nutrients are polymerized into chylomicrons by bile acids, increasing the contact area between fat and enzymes. It is generally believed that conjugated bile acids have better emulsifying lipid properties than the corresponding non-conjugated bile acids. Binding of bile acids to lipase and colipase plays a key digestive role in the duodenum (Knareborg et al., 2003).

2.2 Bile Acid-Intestinal Flora Interaction The modification of primary bile acids by intestinal flora increases the diversity of bile acid pools, including uncoupling, epimerization, dehydroxylation, oxidation and other effects, resulting in a more hydrophobic secondary bile acid pool, which is conducive to the clearance of bile acids in feces (Wahlstr et al., 2016). The composition and abundance of the intestinal flora are in turn influenced by bile acids. Bile acids can shape the intestinal microbial community by promoting the growth of bile acid metabolizing bacteria and disrupting the structure of bile acid intolerant bacteria (Beg-ley et al., 2005). It is generally believed that unbound bile acids are more toxic and can damage bacterial cell membranes, denature proteins, damage DNA, and chelate iron and calcium ions, thereby exerting antibacterial effects (Ur-daneta and Casades, 2017). In vitro experiments have shown that the antibacterial effect of bile acids is independent of their hydrophobicity, as highly hydrophobic LCAs exhibit low antibacterial activity in vitro (An et al., 2022;Tian et al., 2020). In addition, bile acids can also be involved in the regulation of intestinal flora through the indirect role of bile acid receptor-FXR.

2.3 Bile Acid as a Signal Molecule Bile acid as a signal molecule plays a metabolic regulatory role by binding with nuclear receptors-farnesoid X receptor (FXR), vitamin D receptor (VDR), pregnane X receptor (PXR), constitutive androstane receptor (CAR) and membrane receptors-G protein-coupled receptors (GPCRs), participating in lipid and glucose homeostasis, biological metabolism and immune regulatory pathways (Collins, etc, 2023). FXR is the main receptor of bile acids, which is widely distributed in various tissues and organs and plays different physiological functions. For example, FXR-mediated negative feedback mechanism of bile acid synthesis regulation is used as the main regulator of bile acid homeostasis. Liver FXR controls lipogenic genes, while intestinal FXR controls lipid absorption. FXR controls liver lipid through bile acid-dependent reduction of absorption and selective reduction of fatty acid synthesis (Cliford et al., 2021); Bile acid activates FXR to promote fibroblast growth factor 19(FGF19) secretion, and activation of the G protein-coupled bile acid receptor 5(TGR5), which promotes the secretion of glucagon-like peptide -1(GLP-1) from intestinal L cells to regulate glucose metabolism (de Aguiar Vallim et al., 2013). At the same time, bile acids can promote the regeneration of intestinal epithelial cells by activating the TCR5 receptor of intestinal liver cells (Sorrentino et al., 2020). The role of bile acids in the nervous system is also of interest, such as their involvement in the physiological circuit of satiety (Wade et al., 2021); their indirect involvement in neurodegenerative diseases through the blood-brain barrier or acting on gut receptors (E-htezazi et al., 2023).

3) Application of Bile Acid in Animal Husbandry and Aquaculture The Ministry of Agriculture and Rural Affairs included bile acid in the Catalogue of Feed Additives in July 2014. There have been many reports on the addition of bile acids in animal diets, but the results of different scholars on the appropriate amount of bile acids are different. This article reviews the published literature in the past ten years, aiming to provide a reference for the scientific addition of different animal bile acids, and to look forward to the future.

Application of 3.1 Bile Acid in Poultry Breeding At present, the research on dietary bile acid supplementation is mainly based on broilers. Broiler breeds in China mainly include white feather broilers, yellow feather broilers and 817 hybrid broilers. Broilers grow fast and have strong metabolism. Oil is often added to the formula to meet the energy needs of broilers, and it can also provide essential fatty acids to promote the absorption of fat-soluble nutrients and reduce feeding costs. However, the body's own endogenous digestive enzymes and the secretion of bile salts involved in lipid digestion are obviously unable to be fully utilized. The large amount of fat ingested through food intake will cause excessive fat deposition in the body, and even lead to fatty liver and hepatitis, which will bring huge losses to actual production. Especially for young poultry, the imperfect development of liver and gastrointestinal function will bring more severe challenges to the absorption and utilization of nutrients.

4 Outlook

Studies have shown that the appropriate dose of bile acid in the diet can protect animal health and improve growth performance. The basic research work on the metabolic process of bile acid nutrition needs to be more in-depth, and there are the following questions

Problems to be solved:(1) bile acid structure is similar, a wide variety, and host bile acid metabolism and intestinal flora interaction, the formation of intestinal flora-bile acid axis, to determine the different animal bile acid spectrum and the function of each bile acid can make the physiological regulation mechanism more clear, in order to carry out more in-depth experimental research. (2) Most studies use mixed bile acids of pig origin, the main component is porcine deoxycholic acid, but each animal's own bile acid composition is different, its effective components and the regulation mechanism of different animals are still not clear, the effect of a single type of bile acid addition and the appropriate amount of the problem also need to be solved. (3) Different animal species, growth stages and breeding uses have different requirements for exogenous bile acids. In the future, more comprehensive and systematic experimental studies are still needed to integrate a complete system of animal bile acid requirements.

Animals can efficiently use feed nutrients and give full play to the best growth performance, which can not only reduce feed waste, but also promote the healthy and efficient development of the aquaculture industry, which is also a strategic demand to ensure food security in China.

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　　Application of bile acids in livestock and aquaculture

CHEN Yuyan¹,LI Jing'*,LIU Honghe²,FU Shiyi³,GU Xu',LIU Lu⁴,MA Ying'*

　　(1.Institute of Feed Research,Chinese Academy of Agricultural Sciences,Beijing 100081,China;

　　2.Liaoning Inspection,Examination and Certification Center,Shenyang,Liaoning Province 110036,China;

　　3.Jiangxi Agricultural Technology Extension Center,Nanchang,Jiangxi Province 330046,China;

　　4.School of Economics and Management,Beijing Forestry University,Beijing 100083,China)

　　[Abstract]Bile acids are terminal metabolites of cholesterol,which can regulate physiological processessuch as glucose and lipid metabolism,energy metabolism and immune response in the body,and are widelyused as a new type of feed additives in animal husbandry.The physiological functions of bile acids and theircurrent applications in poultry,swine,aquaculture and other animal cultures were summarized in this paper,with a view to providing references for exogenous bile acid additives.

　　[Key words]bile acids;feed additives ;livestock husbandry;aquaculture

Source: China Feed

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