Despite higher economic value of a simplified nursery pig diet compared to a conventional complex diet, a simple diet may stimulate the pig’s immune system and impair intestinal integrity. Dietary Thr supplementation is required when pigs are immunologically challenged to maintain the gut health. Thus, a study was performed to investigate the effects of diet complexity and L-Thr supplementation on growth performance, immune response and gut integrity in nursery pigs. Thirty-two 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. L-Thr was supplemented to each diet to supply either 100% (STD Thr) or 115% (SUP Thr) of the NRC (2012) requirement for Thr. Pigs were individually housed and fed the diets ad libitum for 14 d. All data were analyzed using the MIXED procedure of SAS. Diet complexity, dietary Thr content, and their interactions were considered main effects. Dietary treatment did not affect growth performance. However, pigs fed the simple diet had greater (P < 0.05) plasma interleukin (IL)-10 and IL-6 concentrations compared to those fed the complex diet on d 7 and d 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 to complex diet-fed pigs. The SUP Thr increased (P < 0.05) villus height and goblet cell 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 tended to downregulate (P = 0.10) IL-6 gene expression in the jejunum. Interactions (P < 0.05) between diet complexity and L-Thr supplementation level were observed in goblet cell density in the crypt in the jejunum. In conclusion, SUP Thr in a simple diet would be a nutritional strategy to fortify the gut integrity in nursery pig production, but it does not prevent the induction of inflammation caused by simple diet in nursery pigs.
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