1732 Effect of supplemented mineral phosphorus and fermentable substrates on gut microbiota composition and metabolites, phytate hydrolysis, and health status of growing pigs.

The present study examined the impact of diets with varying CaP levels and fermentable substrates on intestinal CaP concentration, phytate (myo-inositol hexakisphosphate, InsP6) hydrolysis, the intestinal microbiota, and the immune system in pigs. In 2 consecutive experiments, 31 growing pigs (55 ± 4kg) were allotted to a 2 × 2 factorial arrangement with 4 treatment groups, and were fed either a corn-soybean meal or a corn-pea based diet with differences in digestibility, each with 2 different CaP levels (low vs. high, supplemented with monocalcium phosphate). After 3 wks of adaptation to the diets, all pigs were immunized twice with keyhole limpet hemocyanin (KLH) (wk 4 and 6) and blood samples were taken 2 wks after the second immunization. In wk 8, the amount of anti-KLH IgG and anti-KLH IgM were analyzed in blood samples. After slaughtering in wk 9, jejunal and cecal digesta were analyzed for Ca, P, and inositol phosphate isomers, determination of 16S rRNA gene copy numbers by qPCR and bacterial metabolite analyses. Pigs fed the low-CaP diets showed lower plasma anti-KLH IgG concentrations (P < 0.05). The low-CaP level promoted jejunal Bifidobacterium spp. (P < 0.01). For the pea diets, jejunal Lactobacillus spp. were lower (P < 0.05). In the cecum, Eubacterium rectale and Roseburia spp. (P < 0.05) were lower for the low-CaP diets. For the pea diets, the caecal Eubacterium rectale and Bifidobacterium spp. (P < 0.05) were lower. In the cecum, total SCFA, acetate, and propionate (P < 0.01) were lower for the low-CaP diets. Acetate and butyrate (P < 0.05) in caecal digesta were lower for the pea diets. The P net absorption in the jejunum and cecum was lower (P < 0.01) for the low-CaP diets. In addition, the InsP6 hydrolysis in digesta samples was not affected by the dietary treatment, nevertheless the InsP6 concentration in the jejunum was lower for the pea (P < 0.05) and low-CaP diets (P < 0.05). In conclusion, the present study demonstrated that CaP and fermentable substrates modulate the adaptive immune response and the intestinal microbiota, and sufficiently high amounts of CaP may be required to support the adaptive immune response, beneficial saccharolytic bacteria and SCFA production. It needs to be further elucidated whether variations in P digestion and/or absorption might explain the complex relationship between P, the immune system, and the microbial ecosystem.