Dietary high protein-induced diarrhea and intestinal inflammation by activation of NF-κB signaling in piglets

The present study aimed to investigate whether inflammation-associated responses in piglets are induced by high protein (HP) through activating nuclear factor kappa B (NF-κB) signaling. Sixteen piglets (35 d of age, Duroc × [Landrace × Yorkshire], weaned at d 21, initial BW = 9.70 ± 0.11 kg) were allocated to 18% and 26% CP (HP group) at random, comprising 8 replicate pens per treatment. The piglets were slaughtered to collect intestinal tissues when apparent, persistent, and stable diarrhea syndromes happened (on d 12). No significant differences were observed in their growth performance (P > 0.05), but reduction by 19.11%, 25.31%, 23.64% of ADFI, ADG, and G:F, respectively was detected in the HP group. The HP group had greater (P = 0.002) diarrhea rates. Furthermore, dietary HP had lower ileal villus height (VH; P = 0.048), ratio of villus height to crypt depth (VH/CD ratio; P = 0.016), and colonic CD (P = 0.034), as well as had the trend (P = 0.075) to reduce the ileal villus absorptive area. Moreover, HP diets significantly elevated the goblet cell numbers in the ileal villi (P = 0.016) and colonic crypts (P < 0.001) and up-regulated (P = 0.012) the mRNA expression of mucin2 (Muc2) in the ileum. In addition, HP diets increased the myeloperoxidase concentration in the ileum (P = 0.002) and colon (P = 0.007) of piglets. Dietary HP significantly down-regulated the mRNA expression of tumor necrosis factor-α (TNF-α; P < 0.001) in the ileum, induced nitric oxide synthase (iNOS; P = 0.040) and interleukin-22 (IL-22; P = 0.008) in the colon, and inclined to down-regulate interleukin-1β (IL-1β; P = 0.076) expression in the colon. The relative protein abundance of Galectin-3 (P = 0.046) in the colon and the ratio of phosphorylation NF-κB to NF-κB (p-NF-κB/NF-κB ratio) in the ileum of HP piglets were also greater (P = 0.038). These results suggest that dietary HP may cause diarrhea in piglets by activating NF-κB signaling induced intestinal inflammation.