The Effects Of Dietary High Protein On Intestinal Immunity And Barrier Function In Piglets

The study was concentrated on the effects of dietary high protein on intestinal immunity and barrier function in piglets.In the experiment 1,twenty(Duroc × Landrace × Yorkshire)35-day-old piglets were chosen and randomly divided into two groups that contained 18% and 26% crude protein.The piglets were slaughtered for intestinal tissue sampling when obvious and steady diarrhea symptoms occurred.Based on the intestinal morphological structure,serum biochemical indices,serum free amino acid and intestinal inflammation indexes to elucidate the effects of high protein diets on intestinal inflammation and immunity in piglets.The main findings are as follows:(1)Dietary high protein resulted in a significant increase in piglets diarrhea rates(P<0.01).(2)Dietary high protein increased the serum urea nitrogen(BUN)significantly(P<0.01).(3)Supplementation with high protein decreased the contents of Glycine(Gly),Threonine(Thr)and Lysine(Lys)in serum(P<0.05).(4)High-protein diet reduced the jejunal villus width as well as the absorption area of the intestinal villi significantly(P<0.05).Moreover,dietary high protein decreased the ileal villus height,the ratio of villus height: crypt depth(VH:CD),as well as the crypt depth of the cecum and colon significantly(P<0.05).(5)High-protein diet increased the number of goblet cells in the ileal villus and colonic crypt(P<0.05);the content of intestinal myeloperoxidase(MPO)increased significantly(P<0.01);the amounts of intestinal Galectin-3(LGALS3)protein increased significantly(P<0.05),as well as up-regulated the ileal Galectin-1(LGALS1)mRNA expression.Moreover,dietary high protein down-regulated the mRNA expression of ileal TNF-α and colonic IL-22,iNOS and up-regulated the ileal Muc2 significantly(P<0.05).Furthermore,the high-protein diet decreased the abundances of total and phosphorylation protein of NF-κB significantly(P<0.05).In the experiment 2,combined with the detection of tight junction proteins in vivo and based on the metabolomics analysis,four differential metabolites were chosen to treat the porcine intestinal epithelial cell line(IPEC-J2).According to the detection of cell proliferation-toxicity,trans-epithelial resistance and tight junction protein to explain the relationship between diarrhea and intestinal barrier function.The results showed as follows:(1)High-protein diet down-regulated the amounts of intestinal Occludin and ZO-1 protein(P<0.05),as well as the ileal mRNA expression of ZO-1 significantly(P<0.05).(2)L-kynurenine,γ-GABA,and dopamine generally promoted the proliferation of intestinal epithelial cells at low concentrations,while indole inhibited its proliferation in a concentration-dependent manner.(3)Indole,L-kynurenine,γ-GABA and dopamine significantly increased TEER of IPEC-J2 cells with increasing concentration(P<0.05).(4)Compared to the control,indole up-regulated the mRNA expression of ZO-1,Occludin and γ-GABA up-regulated Occludin,Claudin-1 significantly(P<0.05).In summary,this study indicated that dietary high protein resulted in a significant increase in piglets diarrhea rates,altered intestinal morphological structure and intestinal function,and microbial metabolites improved intestinal function and maintained intestinal homeostasis,as well as provided theoretical basis and scientific evidence for regulating intestinal health of piglets.