What Are the Uses of Astragalus Polysaccharides?

Astragalus polysaccharides is a complex, water-soluble neutral polysaccharide extracted from the root of Astragalus, consisting of glucose, arabinose, mannose, galactose, rhamnose and other monosaccharides. As the main component of Astragalus to exert medicinal effects, Astragalus polysaccharide has many physiological functions such as immunomodulation, anti-inflammation, anti-oxidation, anti-tumor, anti-virus, etc. It can also be used as an immune booster and animal feed additive due to its characteristics of no residue, low toxicity and no drug resistance. In chicken production, Astragali polysaccharide can promote growth and development, improve immunization level, and improve animal health, so it has a wide range of application prospects. This paper summarizes the physiological functions of Astragali polysaccharides and reviews the progress of its application in chicken production, aiming to provide reference for the rational development and popularization of Astragali polysaccharides.

1 Physiological functions of Astragali polysaccharide

1.1 Immunomodulatory function

Astragali polysaccharides have the following immunoregulatory functions in animals: one is to promote the development of immune organs such as bursa, thymus and spleen. As the main place for the proliferation and functioning of immune cells, the development of immune organs can determine the immune function of the body. Astragalus polysaccharide can stimulate the development of thymus to promote T cell differentiation, stimulate the development of bursa to promote B cell differentiation, and stimulate the spleen to enhance the effect on lymphocytes, thus exerting the effect of immunomodulation[1]. The second is the effect on immune cells. Astragali polysaccharide can proliferate and activate specific immune cells (T lymphocytes and B lymphocytes), increase the antibody level after vaccination, stimulate the proliferation of non-specific immune cells (NK cells) and enhance their killing power, improve cellular immunity and humoral immune response, and enhance the resistance to external pathogenic microorganisms.

In vitro tests have shown that astragalus polysaccharide can significantly increase the proliferation of chicken T lymphocytes and B lymphocytes and accelerate the transformation of splenic lymphocytes[2] . Through transcriptome and metabolome sequencing, some studies have found that astragalus polysaccharide also exerts immunomodulatory effects on chicken macrophage HD11 through metabolic reprogramming of Toll-like receptor 2 (TLR2) signaling pathway, glycolysis and pentose phosphate pathway[3] . Third, the effect on immune molecules (immunoglobulins and cytokines). Astragalus polysaccharide can promote the production of many kinds of immunoglobulins and cytokines such as interferon (IFN), interleukin (IL), tumor necrosis factor (TNF), and thus participate in the immune response.

1.2 Antioxidant effects

Stress caused by oxidative damage can induce the production of reactive oxygen species in the body, and excessive reactive oxygen species will inhibit the function of related proteins, inducing macronutrient oxidative stress in cells. Astragalus polysaccharides can improve the antioxidant properties of the body, thus realizing its medicinal effects, and attenuating the effects of oxidative stress by increasing the activity of oxidative stress enzymes[4] . Ni Huiyan et al.[5] found that astragalus polysaccharide has a certain scavenging effect on hydroxyl radicals and superoxide anion radicals, and the scavenging ability increases with the increase of its concentration.

1.3 Antiviral effects

Astragalus polysaccharide, as an interferon inducer, can induce the body to produce endogenous interferon, which can produce antiviral proteins and inhibit the synthesis of viral proteins, thus exerting antiviral effects. Astragalus polysaccharide can be used in chicken production to prevent and control Newcastle disease, influenza, infectious bronchitis, chicken infectious laryngotracheitis and other viral infectious diseases.

1.4 Bacteria inhibition

Most plant polysaccharides have natural antibacterial effect. It is found that astragalus polysaccharide has inhibitory effect on Escherichia coli, Salmonella, Staphylococcus aureus, Lactobacillus, Bacillus, Pseudomonas aeruginosa and so on in vitro, and the inhibitory effect is enhanced with the increase of polysaccharide concentration. Ren Zhihua et al[6] found that astragalus polysaccharide could affect the secretion of cytokines such as serum interleukin-17 (IL-17), interleukin-23 (IL-23), transforming growth factor-β (TGF-β), interleukin-10 (IL-10) and other cytokines, and regulate the balance of the subpopulations of helper T-cells 17 (Th17) and regulating T-cells (Treg), thus exerting antimicrobial effects in E. coli. It regulates the balance of the subpopulations of helper T cells 17 (Th17) and regulatory T cells (Treg), thus exerting antimicrobial effect and enhancing immunity.

1.5 Anti-inflammatory effect

Inflammation is a pathological process that occurs in the body in response to various stimuli, such as biological, physical and chemical stimuli, and it will cause inflammatory damage to the body, leading to a decrease in immunity. It has been found that astragalus polysaccharides exhibit immunosuppressive effects and anti-inflammatory activity in inflammatory models. Wang Shiaofei[7] found that astragalus polysaccharide resisted lipopolysaccharide (LPS) infection by decreasing the expression of inflammatory factors and increasing tight junction proteins, and showed anti-inflammatory activity in an in vitro model of inflammation in Caco2 cells. Liu Danhua et al[8] found that in chicken embryo fibroblasts, Astragali polysaccharides alone can promote the release of cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), and thus enhance the immune function; Astragali polysaccharides and LPS co-treatment can inhibit the release of inflammatory factors, such as IL-1β and TNF-α, and thus exert anti-inflammatory effects. Tao Xinlei et al.[9] found that in the LPS-induced macrophage inflammation model in chickens, astragali polysaccharide could inhibit the over-activation of the nuclear factor-κB (NF-κB) p65 and p38 mitogen-activated protein kinase (MAPK) signaling pathways by promoting the expression of cytokine signaling inhibitory factor 3, and then exerted anti-inflammatory effects.

2 Application of Astragalus polysaccharide in chicken production

2.1 Improvement of immune function

Astragali polysaccharides can improve the immune function of chickens through various ways. Li Cheng [10] added different levels of Astragali polysaccharides to broiler diets, and the immune organ indices of fasces, spleen and thymus of broilers in the added group were significantly higher than those of the control group. Sun Bo et al[11] added 500 and 1 000 mg/kg of Astragali polysaccharides to the diets of Wumeng chickens, and the weights of the bursa, thymus and spleen of the added group increased significantly compared with those of the control group, which indicated that Astragali polysaccharides could promote the maturation of immune organs and increase the indexes of immune organs, and that the effect of adding 1 000 mg/kg was better than that of 500 mg/kg. Li Ling[12] found that the spleen index, bursa index and thymus index of broilers fed a basal diet containing 1% astragaloside were significantly higher than those of the control group. In addition, Zhang Bin [13] found that astragalus polysaccharide could also produce immunoprotection for immunosuppressed chicks, which could effectively antagonize the effect of cyclophosphamide on the immune function of the spleen of the chicks, significantly improve the number of T-lymphocytes in immunosuppressed chicks, and increase the content of interleukin-2 (IL-2), thus enhancing the immune function of the spleen of immunosuppressed chicks.

Changes in antibody potency can reflect changes in humoral immune response, and antibody potency after vaccination can directly reflect the effect of vaccine immunization. Studies have found that astragalus polysaccharide has a beneficial effect on antibody levels after vaccination against various avian diseases. Xiang Shuangyun et al.[14] found that astragalus polysaccharide could significantly increase the antibody level (humoral immunity index) and T lymphocyte percentage (cellular immunity index) during immunization of chicken Newcastle disease Lasota vaccine, and it could be used as an immune enhancer of chicken Newcastle disease Lasota vaccine.

Wang Hongcai et al[15] added Astragali polysaccharide to the diluted solution of live Newcastle disease vaccine and immunized chicks with nose and eye drops. The results showed that the serum antibody hemagglutination inhibition (HI) of the test group with the addition of Astragali polysaccharide was significantly higher than that of the unadded group, and the attack protection rate reached 100%, which indicated that Astragali polysaccharide could significantly enhance the immunization effect of the live vaccine against Newcastle Disease. Qiao Haiying et al.[16] found that compared with the vaccine group using the vaccine alone, the combined immunization of astragali polysaccharide and avian infectious bronchitis H120 weak vaccine significantly induced the production of avian infectious bronchitis virus-specific immunoglobulin G (IgG) and secretory immunoglobulin (sIgA) in laying hens and effectively protected chickens against the attack of the virulent strain. The results showed that astragalus polysaccharide could promote the immunization effect of avian infectious bronchitis vaccine. Xu Shuwen et al.[17] showed that the combination of astragalus polysaccharide and simvastatin significantly increased the hemagglutination inhibitory antibody (HIBA) and the serum lgG antibody content.

Miao Zhipeng[18] found that the addition of 0.05% Astragali polysaccharides to the diet significantly enhanced the antibody potency of Newcastle disease and H9 avian influenza virus after immunization with Newcastle disease and H9 avian influenza virus inactivated vaccine, indicating that the use of Astragali polysaccharides can improve the immunization effect of avian vaccines.

Astragali polysaccharides can also regulate the production of immune molecules. Qin Yanjun[19] found that the injection of Astragalus polysaccharide into embryonic eggs could increase the number of mucosal IgA cells and the mRNA expression level of interleukin-2 (IL-2), Toll-like receptor 4 (TLR4), and interferon-gamma (IFN-γ) genes, which could enhance the intestinal immunity of the chicks at the early stage of fledgling to provide the body with effective and timely protection to improve the immune function of the organism. Zhu Yifeng et al.[20] found that astragalus polysaccharide could significantly stimulate the proliferation of peripheral blood, thymus, spleen and bursa lymphocytes, and significantly promote the secretion of cytokines IL-2, interleukin-4 (IL-4), IL-6, IFN-γ and tumor necrosis factor-β (TNF-β), which were also involved in regulating cellular immunity. Li Cheng [10] found that the addition of Astragali polysaccharide to the basal diet of broiler chickens could significantly increase the content of IL-2 and IL-6, and enhance their immune function, and the effect of 0.1% of the additive was better than 0.05%. In addition, Astragali polysaccharide can also regulate the level of peripheral blood T lymphocytes and promote proliferation, in which the level of CD3+ T cells increased linearly with the increase in the amount of Astragali polysaccharide [21].

2.2 Improve growth performance

Astragali polysaccharide can increase the height of intestinal villi, increase the area of small intestinal mucosa, promote the contact between intestines and diets, in order to increase the apparent elimination rate of nutrients in the feed, improve feed utilization, and at the same time, Astragali polysaccharide is also rich in amino acids, vitamins and other nutrients, which can improve the growth performance of animals. Zhang Yong et al [22] found that the addition of low dose (300 mg/kg) and high dose (500 mg/kg) of Astragali polysaccharides to the diet can increase the height of small intestinal villi in Aveeno broiler chickens and reduce the depth of crypt fossa, and the effect of the high dose group was better than that of the low dose group; the mortality rate of the broiler chickens of the high dose group in the experimental period was 0, which was extremely significantly lower than that of the control group.

WANG et al[23] found that adding Astragalus polysaccharide to broiler diets could regulate the structure and quantity of intestinal flora, and then promote the intestinal health of broilers in order to improve the growth performance of broilers. Zhang Long et al.[24] found that the addition of Astragali polysaccharides to diets could significantly increase the average daily weight gain of white-feathered broilers from 1 to 21 and 21 to 42 d, and the body weights of broilers on the 21st and 42nd day of the experiment, and the best effect was achieved with the addition of Astragali polysaccharides at a level of 0.4%. Yang Fu'e[25] found that the addition of Astragali polysaccharide to chicks from 1 day of age could reduce the mortality rate, maintain the homogeneity and increase the weight gain. Wang Hongfang[26] found that the addition of Astragalus polysaccharide to the diet of laying hens can reduce the feed consumption and egg ratio of laying hens, reduce the number of intestinal E. coli, and regulate the balance of intestinal flora, which can improve the intestinal function, promote the digestion and absorption of nutrients in intestinal tract, improve the utilization of feed, and improve the growth performance of chickens.

2.3 Improve production performance

The egg production rate and egg quality of laying hens are important indicators of production performance. Adding Astragalus polysaccharide to the diet of laying hens can promote better absorption and digestion of nutrients. Wang Changye [27] found that the addition of Astragali polysaccharides to the diets of Hyland Brown laying hens could improve egg production rate, reduce the rate of substandard eggs, and improve laying performance, and the greater the amount of Astragali polysaccharides added, the more obvious the improvement effect. Zhang Yao et al.[28] found that the egg production rate, eggshell weight, protein weight and egg haf unit of laying hens with Astragali polysaccharides added to the diet were significantly higher than those of the non-added group, suggesting that Astragali polysaccharides can improve the production performance and egg quality of laying hens. Chen Zhigang [29] found that the addition of Astragali polysaccharides at different levels (100, 200 and 400 mg/kg) significantly increased the daily egg production of Hailan brown shell laying hens, and the higher the addition, the thicker the eggshell thickness, the darker the yolk color, and the egg quality was significantly improved. Liu Bao [30] found that the addition of 200 and 400 mg/kg Astragali polysaccharides to the basal diet could significantly increase the egg production rate of laying hens, reduce the rate of soft-broken eggs, and significantly increase the eggs' haf unit, eggshell strength, and egg shape index, as well as reduce the content of triglycerides in the eggs, and improve the egg quality.

Astragalus polysaccharide can also improve the slaughtering performance and muscle quality of broilers. Sun Bo et al.[11] found that when Astragalus polysaccharide was added to the diets of Wumeng chickens, the slaughtering rate, semi-clearance rate, breast muscle rate, leg muscle rate, rump muscle rate, abdominal fat rate, and meat color redness (a* value) of the experimental group were significantly increased, and the dripping loss and cooking loss were significantly reduced, so that the slaughtering performance and muscle quality of Wumeng chickens were significantly improved. The team also found that astragalus polysaccharides significantly improved the slaughtering rate and other slaughtering performance indexes of yellow-feathered broiler chickens, and also increased the redness (a*), yellowness (b*), drip loss and cooking loss, and improved the slaughtering and muscle quality of broiler chickens[31] . Zhang Long et al.[24] found that the carcass weight and leg muscle weight of white-feathered broilers in the Astragalus polysaccharide test group were significantly increased, and the slaughtering performance of broilers was improved.

2.4 Improvement of antioxidant function

Li Hongquan et al.[32] used Astragali polysaccharide at different doses (0, 2.5, 5.0, 10.0 mg/chick) and in different ways (eye and nose drops, subcutaneous injection, intramuscular injection) in chicks at the ages of 5, 14, and 25 days, and the results showed that the activities of chicken serum superoxide dismutase and glutathione peroxidase increased significantly and the content of malondialdehyde was significantly reduced in each experimental group, which indicated that Astragalus polysaccharide could improve the antioxidant function of chickens. The results showed that the activities of serum superoxide dismutase and glutathione peroxidase were significantly increased and malondialdehyde content was significantly reduced in all the test groups, indicating that astragalus polysaccharides could improve the antioxidant effects in chickens.

Jin Luyang et al.[33] found that when chicks were injected subcutaneously with different concentrations of Astragali polysaccharides at the age of 1 day, the activities of superoxide dismutase, glutathione peroxidase, catalase, glutathione reductase and malondialdehyde in the serum were increased and malondialdehyde level was decreased, indicating that Astragali polysaccharides improved the antioxidant capacity of chicks. Zhang Youzeng[34] found that compared with the control group, the superoxide dismutase activity in the blood serum of broilers in the test group supplemented with 0.5% Astragali polysaccharides increased by 6.30%, and the malondialdehyde content decreased by 5.94%. Lipids in eggs are prone to peroxidation, resulting in oxidation of lutein and lightening of egg yolk color. Adding Astragalus polysaccharide to the diet can improve the color of egg yolk. Lin Xiajing et al.[35] found that when Astragalus polysaccharide was added to the diets of yellow-feathered broiler hens, the egg yolk color of the 200 mg/kg Astragalus polysaccharide group was significantly higher than that of the control group.

2.5 Prevention and treatment of diseases

Astragali polysaccharide can prevent bacterial and viral infections through antibacterial and antiviral effects, and comprehensively enhance the immune function of chickens, so as to reduce the incidence of disease and mortality rate, improve the cure rate, and play the role of disease prevention and treatment. Hu Yuanliang et al.[36] added Astragalus polysaccharide into chicken embryo fibroblasts cultured for 24h, and then inoculated with Newcastle disease virus after 12h of culture, after which the activity of chicken embryo fibroblasts was measured by neutral red dye uptake method. The results showed that astragalus polysaccharide promoted the proliferation of Newcastle disease virus-infected chick embryo fibroblasts, and promoted the cells to resist the infection of Newcastle disease virus. Meng Xianrong et al[37] infected broiler chickens artificially with strong viruses of Marek's disease, and found that the injection of a certain concentration of Astragali polysaccharides could increase the activity of macrophages and the in vitro induced viability of interferon, reduce the morbidity and mortality of infectious bursal disease, and inhibit the infection of Marek's disease and the occurrence of tumors.

Yu et al[38] found that a certain concentration of astragalus polysaccharide could significantly reduce the morbidity and mortality of chicken infectious bursal disease, and enhance the body's resistance to infectious bursal disease. Liu Lichun et al.[39] found that intramuscular injection of 2 mL/kg of Astragalus polysaccharide had significant preventive and therapeutic effects on infectious laryngotracheitis in chickens, and the recovery rate was significantly higher than that of the control group. It was also found that injection of Astragali polysaccharide into 3-day-old chicks infected with strong viruses of avian myeloid leukemia could reduce the morbidity and mortality of avian myeloid leukemia[40-41] . Mu Feiyan et al.[42] found that the addition of Astragalus polysaccharide to chicken diets could inhibit the growth and reproduction of pathogenic bacteria that cause diarrhea and intestinal inflammation, and reduce the number of Escherichia coli in the cecum of laying hens.

3 Outlook

Under the background of “no-antibiotic” culture, Astragali polysaccharide can improve the growth and production performance of animals through immunomodulation, antioxidant, antiviral, bacterial inhibition and anti-inflammatory effects, and play a role in the organism through multi-level and multi-pathway, so that Astragali polysaccharides can be substituted for antibiotics as an additive for animal feed, immunity enhancer and animal disease prevention and treatment drug. It can replace antibiotics as animal feed additives, immunity enhancers, and drugs for prevention and control of animal diseases, and play its role in increasing production and medicinal value in chicken production. In the future, we should explore the optimal amount of Astragali polysaccharides, explore the synergistic effect of Astragali polysaccharides with antibiotics, drugs, probiotics, etc., and evaluate the effect of resistance to animal diseases, so as to promote the green, healthy and efficient development of China's poultry industry.

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