Effects of increasing dietary trypsin inhibitor levels on growth performance, diarrhea incidence, gut inflammatory responses, oxidative stress, morphology, barrier integrity, and hindgut fermentation of nursery pigs.

This study was conducted to evaluate the effects of increasing trypsin inhibitor (TI) levels in nursery diets on growth performance and intestinal function of nursery pigs. A total of 120 newly weaned piglets (5.16 ± 1.03 kg initial body weight; weaned at 18.1 ± 1.48 d of age) were allotted to 5 treatments in 6 replicates with 4 pigs per pen for a 28-d trial. Dietary treatments were increasing TI levels at 1.5, 3.1, 4.8, 6.4, and 8.0 TIU/mg, achieved by graded inclusion of raw soybean. At d 28 postweaning, blood, intestinal mucosa, intestine, digesta, and fecal samples were collected. Increasing dietary TI levels linearly decreased final body weight and average daily gain, average daily feed intake, and gain-to-feed ratio during the overall nursery period (P < 0.05) but increased diarrhea incidence up to d 21 postweaning (P < 0.05). In jejunal mucosa, increasing dietary TI levels increased interleukin-8 concentrations linearly (P < 0.05) and tumor necrosis factor-α concentrations quadratically (P < 0.05), while increasing interleukin-8 and interferon-γ linearly in ileal mucosa (P < 0.05). Calprotectin levels tended to increase linearly in colon digesta (P = 0.07) and feces (P = 0.07) with increasing dietary TI levels. In jejunum, mucosal catalase levels linearly decreased (P < 0.05) with increasing dietary TI levels, while mucosal protein carbonyl levels in ileum linearly increased (P < 0.05). Serum diamine oxidase levels tended to decrease linearly (P = 0.07) and serum urea nitrogen had a quadratic response (P < 0.05) with increasing dietary TI levels. In duodenum and ileum, increasing dietary TI levels linearly decreased villus height and increased crypt depth, resulting in a linear reduction in villus height-to-crypt depth ratio (P < 0.05). In jejunal mucosa, increasing dietary TI levels linearly increased mucin-2 (P < 0.05) levels and tended to linearly increase occludin levels (P = 0.06). Increasing dietary TI levels linearly decreased fecal acetate (P < 0.05) and total short chain fatty acid (P < 0.05) concentrations and tended to linearly decrease fecal butyrate (P = 0.07) concentrations, while fecal isobutyrate and isovalerate concentrations tended to increase quadratically (P < 0.10). In conclusion, increasing dietary TI levels negatively affected growth performance and indicators of intestinal function in nursery pigs, as evidenced by impaired gut morphology, alterations in intestinal barrier-related markers and short chain fatty acid production, and increased inflammation in nursery pigs.