Effect of dietary fiber and threonine content on intestinal barrier function in pigs challenged with either systemic E.coli lipopolysaccharide or enteric Salmonella Typhimurium

Background:The independent and interactive effects of dietary fiber(DF)and threonine(Thr)were investigated in growing pigs challenged with either systemic E.coli lipopolysaccharide(LPS)or enteric Salmonella Typhimurium(ST)to characterise their effect on intestinal barrier function.Results:In experiment 1,intestinal barrier function was assessed via oral lactulose and mannitol(L:M)gavage and fecal mucin analysis in pigs challenged with E.coli LPS and fed low fiber(LF)or high fiber(HF)diets with graded dietary Thr.Urinary lactulose recovery and L:M ratio increased(P<0.05)during the LPS inoculation period in LF fed pigs but not in HF fed pigs.Fecal mucin output was increased(P<0.05)in pigs fed HF compared to LF fed pigs.In experiment 2,RT-qPCR,ileal morphology,digesta volatile fatty acid(VFA)content,and fecal mucin output were measured in Salmonella Typhimurium challenged pigs,fed LF or HF diets with standard or supplemented dietary Thr.Salmonella inoculation increased(P<0.05)fecal mucin output compared to the unchallenged period.Supplemental Thr increased fecal mucin output in the HF-fed pigs(Fib×Thr;P<0.05).Feeding HF increased(P<0.05)VFA concentration in cecum and colon.No effect of either Thr or fiber on expression of gene markers was observed except a tendency(P=0.06)for increased MUC2 expression with the HF diet.Feeding HF increased goblet cell numbers(P<0.05).Conclusion:Dietary fiber appears to improve barrier function through increased mucin production capacity(i.e.,goblet cell numbers,MUC2 gene expression)and secretion(i.e.,fecal mucin output).The lack of effect of dietary Thr in Salmonella-challenged pigs provides further evidence that mucin secretion in the gut is conserved and,therefore,Thr may be limiting for growth under conditions of increased mucin production.