Effects Of Plant Polysaccharides On Growth Performance,Immune Function And Intestinal Health In Weaned Piglets

The present study was conducted to investigate the effects of Astragalus polysaccharides(Aps)and Ginseng polysaccharide(Gps)on growth performance,immune function and intestinal health in weaned piglets.The Aps was extracted from the tubers of Astragalus mongolica and Gps was extracted from the rhizomes of Ginseng ginseng provides the data support for the application of plant polysaccharides as antibiotic substitutes.This study was divided into three experiments.In experiment 1,Lps used to stimulate mouse macrophages(RAW264.7)to explore the regulatory effect of two plant polysaccharides on immune stress stimulated by Lps.In experiment 2,28-day-old weaned piglets were selected to explore the effects of two plant polysaccharides on growth performance,immune function and intestinal microflora in weaned piglets.In experiment 3,on the basis of experiment 2,some piglets were stimulated by Lps to explore the immunomodulatory effects and related mechanisms of two plant polysaccharides in piglets.Experiment 1: Different concentrations of Aps and Gps were added to macrophages(RAW264.7)stimulated by Lps to explore the cell morphology,enzyme activity,inflammatory factors and gene expression of TLR4 signaling pathway in different treatment groups.The results showed that Lps impaired cell morphology and slowed down cell proliferation.The contents of LDH,ACP,AKP,IL-1βand TNF-α in cell supernatant were significantly higher than those in negative control group(p < 0.05).The expressions of TLR4,MyD88 and NF-κB in Lps group were significantly higher than those in negative control group(p < 0.05).Plant polysaccharides were helpful to restore cell morphology and proliferative activity damaged by Lps.The contents of LDH,ACP,AKP,IL-1β and TNF-α in supernatant of cells treated with different concentrations of Aps and Gps were significantly lower than those in Lps group(p < 0.05),and the dose of Aps at 1 mg/ml was optimum After treatment with Aps and Gps,the expressions of TLR4,MyD88 and NF-κB in cells were significantly lower than those in Lps group(p <0.05).The results indicated that Aps and Gps alleviated Lps-induced inflammatory response and reduced immune stress by inhibiting the activation of TLR4/NF-κB.Experiment 2: A total of 180 weaned piglets(Duroc × Landrace × Yorkshire)were randomly assigned to three treatment groups,each group contained 6 pens per treatment,and 10 animals per pen.The treatment group 1 was the control group(Con),fed with basic diet.The treatment group 2 was the Aps group,fed with basic diet with 800mg/kg Aps.The treatment group 3 was the Gps group,fed with basic diet with 800mg/kg Gps.The experiment lasted for 28 days.Piglets were weighed individually at the beginning and end of the experiment.Feed intake and the rate of diarrhea were counted.Average daily feed intake(ADFI),average daily gain(ADG),and feed to gain(F:G)for each pen were calculated.On day 14 and 28,six piglets per treatment were randomly selected for blood sample collection to further analysis.At 28 d,one pig per pen were slaughtered and sampled.Colon contents were collected for the detection of VFAs and high throughput sequencing.Piglets fed Aps or Gps had higher ADG compared to the Con group(P < 0.05).A reduced F:G and diarrhea rate were observed in Aps and Gps piglets(P < 0.05).Aps piglets exhibited higher IgA and IgM levels(P < 0.05).Aps and Gps piglets also had higher concentrations of acetic acid,isobutyric acid,and butyrate in their colon(p < 0.05).Result of high-throughput sequencing revealed that Aps and Gps affected bacterial quantity and diversity in the colon.Aps piglets had a higher relative abundance of Lactobacillus gasseri and Lactobacillus amylovorus(p < 0.05),and the Aps and Gps piglets also had a higher relative abundance of Lachnospiraceae,Melainabacteria and Selenomonadales(p < 0.05).The results showed that Aps and Gps enhanced the immune function of piglets,changed the composition of intestinal microorganisms and increased the content of VFAs in intestine,thus improving the growth performance of weaned piglets.Experiment 3 was conducted on the basis of the experiment 2.On day 29,twelve piglets were selected from each group.Six of them were injected with 25 ug/kg body weight Lps,and the other six were injected with saline of equal volume.At 1.5 and 3 hours after treatment,blood samples were collected for the determination of serum biochemical and immune indices.At 4 hours after treatment,12 piglets in each group were slaughtered.Jejunum and jejunum mucosa were taken to determine the intestinal morphology,the expression of intestinal tight junction protein and the expression of immune signal pathway protein.The results showed that Aps and Gps alleviated the immune stress induced by Lps stimulation in piglets,significantly reduced the levels of ALB,BUN,ALT,AST,IL-1β and TNF-α in serum induced by Lps stimulation,which also increased the levels of SOD,T-AOC and IgA in piglets(p< 0.05).The results of jejunal morphology showed that Aps and Gps significantly increased the height of jejunal villi(p < 0.05),decreased the recess depth(p < 0.05),and alleviated the damage of Lps to jejunal villi.The results of intestinal barrier function showed that both Aps and Gps alleviated the down-regulation of the expression of Occludin and Claudin in jejunum stimulated by Lps,and contributed to the protection of intestinal barrier function.Immunohistochemical and immunofluorescence results showed that Lps stimulation significantly increased the expression of TLR4,MyD88 and NF-κB in jejunal mucosa(p < 0.05),while Aps and Gps inhibited the expression of TLR4,MyD88 and NF-κB protein(p < 0.01),and reduced the positive rate of NF-κB p65 induced by Lps stimulation.The results indicated that Aps and Gps reduced liver injury and secretion of inflammatory factors,improved antioxidant capacity and intestinal barrier function,which alleviated excessive immune stress by regulating intestinal TLR4/NF-κB signaling pathway.In conclusion,dietary supplementation with Aps or Gps improved the growth performance in weaned piglets,enhanced the immune function,contributed to the balance of intestinal microorganisms,increased the content of VFAs in intestinal tract,which reduced the liver damage and the secretion of inflammatory factors caused by Lps stimulation,improved the antioxidant capacity and intestinal barrier function in Lps challenged piglets,and alleviated excessive immune stress by regulating the intestinal TLR4/NF-κB signaling pathway.