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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.

The aim of this experiment was to investigate the effects of dietary crude protein (CP) contents and crystalline amino acids (CAA) supplementation patterns on growth performance, intestinal histomorphology, and immune response in weaned pigs under clean (CSC) or unclean sanitary conditions (USC). A total of 144 weaned pigs (6.35 ± 0.63 kg body weight) were assigned to 6 treatments in a 3 × 2 factorial arrangement based on CP content and sanitary conditions using a randomized complete block design, giving 8 replicates per treatment with 3 pigs per pen. Pigs were fed one of three diets for 21 d: one high CP (HCP ; 22%) and two low CP (LCP ; 19%) diets supplemented with 9 indispensable AA or only 6 AA (Lys, Met, Thr, Trp, Val, and Ile) as CAA. The CSC room was washed weekly, whereas the USC room had sow manure spread in the pens and was not washed throughout the experiment. Body weight and feed disappearance were recorded weekly. Blood was sampled from 1 pig per pen weekly, and the same pig was euthanized for jejunal tissues sampling on day 21. Pigs raised under USC had reduced (P < 0.05) average daily gain (ADG) and gain to feed ratio (G:F) in week 2, but contrary results that greater (P < 0.05) ADG and G:F were found in pigs under USC in week 3. Overall, there was an interaction where G:F did not differ between HCP and LCP under CSC, however, LCP decreased (P < 0.05) G:F compared to HCP under USC. Pigs fed the HCP diet had higher (P < 0.05) fecal scores than those fed the LCP diets throughout the experiment. Pigs fed the LCP had higher (P < 0.05) villus height to crypt depth ratio than those fed the HCP. An interaction was observed where goblet cell density in the jejunum was higher (P < 0.05) in pigs fed LCP than HCP under CSC, but no difference was found between HCP and LCP under USC. Different CAA supplementation patterns did not influence both growth performance and histomorphology. Pigs raised under USC had greater (P < 0.05) plasma interleukin (IL)-10 and IL-6 concentrations and reduced (P < 0.05) plasma tumor necrosis factor-alpha concentration. Also, the LCP diets resulted in a greater (P < 0.05) plasma IL-10 concentration. In conclusion, overall growth performance did not differ between HCP and LCP under CSC, but LCP diets reduced G:F under USC. Feeding LCP diets to weaned pigs improved gut morphology under USC and ameliorated systemic inflammation induced by USC, whereas CAA supplementation patterns did not affect growth performance and gut morphology. [ABSTRACT FROM AUTHOR]