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

Abstract

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.

Intestinal Health and Threonine Requirement of Growing Pigs Fed Diets Containing High Dietary Fibre and Fermentable Protein

“…Previous studies have reported a reduced efficiency of utilizing dietary Thr for PD with increasing DF content, thereby increasing the dietary Thr requirement growth [2,8,9]. This effect is largely attributed to increased endogenous protein/AA losses [7,13,32]. In the present study, we observed that the HF diet reduced ATTD of N, which is consistent with reports from previous studies [2,8], but no significant effect of fCP was observed.…”

“…Gene expression analysis showed significant treatment effects on target genes only in the colon. In the colonic tissue, feeding the HfCP diet reduced the expression of MUC2 gene, with no effect on MUC5ac, while feeding high DF increased the expression of both MUC2 and MUC5ac genes, which agrees with previous reports [14,31,32]. Expression of MUC2 was previously shown to be correlated with mucin secretion [31] which increases Thr requirements for protein deposition [2].…”

Physiological Functions of Threonine in Animals: Beyond Nutrition Metabolism

“…In addition, many recent studies have focused on the influence of the relationship between dietary Thr and dietary fiber on intestinal barrier function [ 85 , 86 , 87 ]. Dietary fiber has positive effects on barrier function by boosting mucus secretion and mucin synthesis [ 88 ].…”

“…Dietary fiber has positive effects on barrier function by boosting mucus secretion and mucin synthesis [ 88 ]. However, high dietary fiber increases the loss of endogenous amino acids, resulting in a greater need for Thr to maintain mucin production [ 85 , 89 ]. The effect of Thr on intestinal barrier protein is influenced by the amount of fiber in the diet.…”

Regression-Derived Ileal Endogenous Amino Acid Losses in Broiler Chickens and Cannulated Pigs Fed Corn Fiber, Wheat Bran, and Pectin

“…Several factors, including dietary protein and fiber levels, could influence ileal EAA losses in non-ruminant animals [ 1 , 4 ]. Dietary fiber contributes to an increase in EAA losses because of its effects on mucous secretion and cell proliferation [ 6 ]. In order to obtain consistent and reliable EAA losses data for standardization of apparent ileal amino acid digestibility values, it is important to evaluate the effect of different dietary components, such as fiber type (soluble vs. non-soluble) and viscosity, of feed ingredients on basal ileal EAA flow.…”