Effects of dietary crude protein content and resistant starch supplementation on growth performance, intestinal histomorphology and microbial metabolites in weaned pigs.

A 4-week study was conducted to evaluate the effects of dietary crude protein (CP) content and resistant starch (RS) supplementation on growth performance, intestinal histomorphology and microbial metabolites of weaned pigs. A total of 96 pigs (7.06 ± 0.45 kg body weight) were assigned to 1 of 4 diets in a randomised complete block design involving a 2 (CP levels) × 2 (without or with RS) factorial arrangement to give 8 replicate pens and 3 pigs per pen. Body weight and feed disappearance were recorded weekly, and the faecal consistency score was determined every morning. Blood was sampled on days 1, 14 and 28 from one pig per pen, and the same pig was euthanised on day 28 to collect ileal tissue and ileal and colon digesta. Data were analysed using the MIXED procedure of SAS. The average daily gain and gain:feed ratio were lower (p < 0.05) in pigs fed low crude protein (LCP) diets compared to those fed high CP (HCP) diets during week 3 and overall period. The analysed Lys, Met+Cys and Thr in feed were lower than calculated values, particularly in LCP diets, which may have affected performance. Pigs fed the LCP diets had longer (p < 0.05) ileal villi and higher villus height to crypt depth ratios than those fed the HCP diets, and RS supplementation increased (p < 0.05) ileal villus height. Interactions (p < 0.05) between dietary CP content and RS inclusion were observed for short-chain fatty acid concentration in the ileum and colon in phase 2. There was no difference in propionic acid (ileum) or butyric acid (colon) concentrations among pigs fed HCP diets, however, the butyric acid concentration increased in pigs fed the LCP diet when supplemented with RS. Reducing dietary CP lowered (p < 0.05) faecal score, plasma urea nitrogen and digesta ammonia content. Overall, feeding LCP diets reduced growth performance but improved gut morphology in weaned pigs. Feeding the LCP diet with RS supplementation modulated concentrations of ileal propionic acid and colonic butyric acid in weaned pigs.