Diet complexity and l-threonine supplementation: effects on growth performance, immune response, intestinal barrier function, and microbial metabolites in nursery pigs

Abstract

The aim of this study was to investigate the effects of diet complexity and l-Thr supplementation level on the growth performance, immune response, intestinal barrier function, and microbial metabolites in nursery pigs. Thirty-two weaned pigs (body weight 7.23 ± 0.48 kg) were randomly assigned to dietary treatments in a 2 × 2 factorial arrangement based on diet complexity (complex or simple) and dietary Thr content. The complex diet contained fish meal, plasma protein, and dried whey to mimic a conventional nursery diet. The simple diet was formulated with corn, wheat, and soybean meal and did not contain any animal products. l-Thr was supplemented to each diet to supply either 100% (STD Thr) or 115% (SUP Thr) of the NRC (2012) requirement for standardized ileal digestible Thr. Pigs were individually housed and fed experimental diets ad libitum for 14 d. Diet complexity, dietary Thr content, and their interactions were considered the main effects. Pigs fed the simple diet had greater (P < 0.05) plasma interleukin (IL)-10 and IL-6 concentrations compared with those fed the complex diet on days 7 and 14, respectively. Simple diet-fed pigs tended to show greater (P < 0.10) expression of genes encoding for tumor necrosis factor-α, claudin-1, and zonula occludens-1 in the jejunum compared with complex diet-fed pigs. The simple diet-fed pigs had greater (P < 0.05) concentrations of NH3-N in the jejunum digesta than did complex diet-fed pigs. The SUP Thr increased (P < 0.05) villus height and goblet cell (GC) density in villi and crypts in the jejunum and deepened (P < 0.05) crypts in the proximal colon. The SUP Thr resulted in the upregulation (P < 0.05) of occludin gene expression and a tendency toward the downregulation (P = 0.10) of IL-6 gene expression in the jejunum. Interactions (P < 0.05) between diet complexity and l-Thr supplementation level were observed in GC density in the crypt, NH3-N concentration in the jejunum, and the contents of acetate, propionate, and total volatile fatty acids in the colon. In conclusion, feeding a simple diet to nursery pigs resulted in systemic and intestinal inflammation. The SUP Thr diet did not normalize the simple diet-induced inflammation but improved gut integrity. SUP Thr seems to have greater benefits with a simple diet than with a complex diet. Therefore, SUP Thr in a simple diet could be a beneficial nutritional strategy for enhancing gut health.

Physiological Functions of Threonine in Animals: Beyond Nutrition Metabolism

“…One of the explanations for this effect might be that Thr promotes mucin secretion, because mucins cannot be digested in the small intestine and, therefore, arrive to the large intestine, where they serve as the substrates for saccharolytic bacteria [ 73 ]. Koo et al [ 74 ] found that the supplementation of Thr 15% higher than the NRC recommendation can interact with feed composition to alter gut microbial fermentation. The data also imply that Thr has beneficial effects on intestinal microbiota which might be related to mucin synthesis and immunoglobulin production as a result of Thr addition [ 72 ].…”

Invited Review: Maintain or Improve Piglet Gut Health around Weanling: The Fundamental Effects of Dietary Amino Acids

“…Dietary Thr supply is critical for gut morphological maintenance and development because Thr plays a key role in mucin synthesis and barrier integrity [ 13 , 15 , 41 ]. Ren et al [ 42 ] and Koo et al [ 43 ] both reported that dietary supplementation of Thr above the NRC [ 23 ] requirement enhanced intestinal morphology as reflected in the improved VH, CD, and VCR in weaned pigs. The density of goblet cells in the jejunal villi and crypts was also increased upon dietary Thr supplementation [ 43 ].…”

“…Ren et al [ 42 ] and Koo et al [ 43 ] both reported that dietary supplementation of Thr above the NRC [ 23 ] requirement enhanced intestinal morphology as reflected in the improved VH, CD, and VCR in weaned pigs. The density of goblet cells in the jejunal villi and crypts was also increased upon dietary Thr supplementation [ 43 ]. Either deficiency or excess of dietary Thr has adverse effects on the synthesis of intestinal mucosal proteins such as mucins in young pigs [ 44 ].…”

“…One of the explanations for this effect might be the up-regulation of mucin gene expression, because mucins cannot be digested in small intestine and thereby will reach ceca, acting as a substrate for saccharolytic bacteria. In nursery pigs, Koo et al [ 43 ] reported that the supplementation of Thr 15% above the NRC [ 27 ] requirement (on the standardized ileal digestible basis) seemed to modify intestinal microbial fermentation in an interactive manner with diet composition. Thr supplementation in a simple diet (contained soybean meal as a protein source) decreased the intestinal NH 3 content but increased the intestinal volatile fatty acid content when compared with a complex diet (contained various sources of animal protein) [ 43 ].…”

“…Some studies indicated that Gly has a protective effect in mesenteric ischemia/reperfusion injury through the inhibition of apoptosis [ 102 ], while others have shown that Gly protection against intestinal ischemia/reperfusion injury is reached by a mechanism that is consistent with Gly uptake [ 103 ]. Although it seemed that dietary Thr supplementation did not normalize the gut inflammation induced by feeding a soybean meal based simple diet (without animal proteins) to weanling pigs [ 43 ], Chen et al [ 104 ] reported that Thr supplementation (at 3.0 g/kg diet) could attenuate LPS-induced inflammatory responses in young broilers, as indicated by the reversed LPS-induced increase in the concentrations of pro-inflammatory cytokine in serum, spleen, and intestinal mucosa.…”