Effects of dietary protein content and crystalline amino acid supplementation patterns on growth performance, intestinal histomorphology, and immune response in weaned pigs raised under different sanitary conditions

Abstract

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.

Keywords: crystalline amino acids; low protein diet; piglets; sanitation.

Figure 1.

Effect of dietary crude protein content and sanitary conditions on fecal score of weaned pigs (0 = normal; 1 = soft feces; 2 = mild diarrhea; and 3 = severe diarrhea). Clean_HCP, high crude protein under clean sanitary conditions; Clean_LCP 1, low crude protein supplemented with all indispensable amino acids except Arg under clean sanitary conditions; Clean_LCP 2, low crude protein supplemented with six essential amino acids (Lys, Met, Thr, Trp, Val, and Ile) under clean sanitary conditions; Unclean_HCP, high crude protein under unclean sanitary conditions; Unclean_LCP 1, low crude protein supplemented with all indispensable amino acids except Arg under unclean sanitary conditions; Unclean_LCP 2, low crude protein supplemented with 6 essential amino acids (Lys, Met, Thr, Trp, Val, and Ile) under unclean sanitary conditions. Unclean sanitary condition increased (P < 0.05) the incidence of diarrhea of weaned pigs in week 2 compared to clean sanitary condition, and pigs fed the HCP diet had higher (P < 0.05) fecal scores throughout the experiment than those provided LCP diets regardless of sanitary conditions.

Figure 2.

Effect of dietary crude protein content and sanitary conditions on the flux of fluorescein isothiocyanate dextran 4 kDa (FD4) flux in the jejunum. HCP = high crude protein, LCP 1 = low crude protein supplemented with all indispensable crystalline amino acids except Arg, LCP 2 = low crude protein supplemented with six indispensable crystalline amino acids (Lys, Met, Thr, Trp, Val, and Ile). Unclean sanitary conditions decreased (P < 0.05) ex vivo gut permeability measured by using FD4 flux, however, no interaction between protein contents and sanitary conditions was observed.