Effects Of Dietary Yeast Culture On Intestinal Microbial Fermentation And Microbiota And Immune Functions Of Growing-finishing Pigs In Summer

The high temperature and humidity in summer is a big challenge to growing-finishing pigs in Jiangsu southwards, which may destroy the metabolic balance of normal microorganisms in gastrointestinal tract and cause dysfunction of digestion, absorption and immunity consequently. Yeast culture (YC) is a mixture of yeast cells, fermented media and metabolites of yeast fermentation. It comprises of oligosaccharides, amino acids, peptides, proteins, organic acids, vitamins, yeast sourced enzymes and other unknown growth factors which are the main substrates of beneficial bacteria in gastrointestinal tract. Therefore, YC is able to regulate the balance of gut microecology and stimulate certain immune responses. This trial was conducted to investigate the effects of YC on intestinal microbiota, microbial fermentation and certain immune functions of growing-finishing pigs in summer. This thesis was described in the following three sections.Section1:In vivo production of VFA was always companied by consistently absorption, thus the chyme levels of VFA might be not able to precisely evaluate the real production of VFA. An in vivo animal trial and two batches of in vitro fermentation were respectively designed to investigate the effects of YC on microbial fermentation of G-F pigs in summer. For in vivo trial,180pigs (Duroc×Landrace×Yorkshire) at the age of70days, with an average initial body weight of29.56±1.12kg kg, were randomly allotted to one of three dietary treatments on the basis of body weight and gender. Every treatment will be made up of6replications with10pigs per replication. The control dietary was a basal corn-soybean meal diet. Treatment1and2were corn-soybean meal+YC diet, with1g/kg·DM and4g/kg-DM YC, respectively. The whole trail period are95days, including growing-(30kg-60kg) and finishing-phase (60kg-100kg). At the end of growing phase (60kg of weight) and the end of finishing phase (100kg of weight)1pig of each replication of each group were slaughtered, respectively. VFA values (acetate, propionate and butyrate) of ileum and colon chymes were detected by GC and lactate by colorimetric technique. For in vitro fermentation, ileum chymes as substrates and colon chymes as inocula was in order to simulation intestinal microbial fermentation of ileum chymes in colon. Design of in vitro fermentation as follows (1) same substrate (ileal chymes from pigs of control group) with different inocula (colon chymes from pigs of C,T1and T2group respectively) to reflect the effect of YC on colon microbial activity;(2) different substrates (ileal chymes from pigs of C,T1and T2group) with same inoculum (colon chymes from pigls of control group) to reflect the effect of YC on fermentive activity of ileum chymes;(3) substrates (C,T1and T2ileum chymes) with corresponding inoculum (C,T1and T2colon chymes) to synthetically evaluate the effect of YC on intestinal microbial fermentation. VFA (acetate, propionate and butyrate) and lactate values detected after37℃fermentation for24h. The results of in vivo trial showed that YC could change ileal concentration of lactate and VFA in certain degree. Ileal level of propionate in T2group of growing pigs was significantly higher than in control group and T1(P<0.05). Ileal level of butyrate in T2group of growing pigs was significantly lower than in control group (P<0.05). Ileal level of lactate in T1and T2groups of growing pigs was significantly lower than in control group (P<0.05) and (P<0.01). Ileal level of lactate in T1group of finishing pigs was significantly lower than in control group (P<0.05).YC had no influence on colonic level of lactate and VFA (P>0.05).YC had no effects on colonic chymes concentration of lactate and VFA of G-F pigs. In vitro fermentation experiment one showed that YC had elevated colon microbial fermentive activity with ileal chymes. Butyrate in C-T1group of growing pigs was significantly higher (P<0.05) as compare to C-C. Colonic microbial fermentive activity in treatment groups of finishing pigs had tended to increase (P>0.05) as compare to control group. In vitro fermentation experiment two showed that YC had significantly elevated ileal chymes fermentive activity. Level of TVFA and other VFAs in T1-C group of growing pigs were significantly higher (P<0.01) than in C-C group. Level of TVFA and acetate and butyrate in T2-C group of growing pigs were significantly higher (P<0.01) than in C-C group. All groups had comparable level of TVFA and other VFAs (P>0.05) of finishing pigs. In vitro fermentation experiment three showed that YC had significantly elevated (P<0.01) the butyrate production of intestinal microbial fermentation of growing pigs. All groups had comparable level of TVFA and other VFAs (P>0.05) of G-F pigs. Synthetic research on above results, we can concluded that YC had significantly decreased ileal level of lactate and significantly enhanced level of VFA fermented by intestinal microbial, especially level of butyrate. Therefore be helpful to mitigate damage of intestinal microecology by heat stress.Section2:This experiment was aim to investigate the effect of YC on the composition intestinal microbiota and the numbers of predominant bacteria of G-F pigs in summer. Experimental design and sampling of ileal and colonic chymes were the same as above in vivo trial. PCR/DGGE based on16S rRNA gene was used to investigate structural changes of micro-flora in ileum and colon. Quantitative Real-time PCR was used to assay numbers of total bacteria and Lactobacilli in ileal and colonic chymes. Semi-quantitative PCR was used to assay numbers of butyrate-producing bacteria in colonic chymes. The results showed that YC had the potential to change the composition of micro-flora in ileal and colonic chymes. DGGE profiles from ileal or colonic chymes of two YC groups revealed much more similarity as comparing to which from control group (P>0.05). YC had no significant effect on number of total bacteria in ileal and colonic chymes of G-F pigs. The numbers of Lactobacilli in ileal chymes of YC groups of G-F pigs were significantly lower (P<0.05) than that of control group.However, all groups had comparable number of Lactobacilli (P>0.05) in colonic chymes of G-F pigs. The number of butyrate-producing bacteria in colonic chymes tended to increase (P>0.05) in YC groups. In conclusion, dietary YC could increase the similarity and stability of G-F pigs’intestinal bacterial communities in summer. YC significantly decreased number of Lactobacilli in ileal chymes, and tended to increase number of butyrate-producing bacteria in colonic chymes. These results were parallel with which got from above in vitro fermentation, that YC decreased ileal level of lactate and increased level of butyrate. Thus, YC might mitigate the damage of heat stress on intestinal microecology through maintaining structural stability of intestinal bacterial communities.Section3:This experiment was conducted to investigate the effects of YC on certain immune functions of G-F pigs in summer. The experimental design was the same as above. After slaughtering, immune organ indices were calculated by weighting thymus, spleen and liver. Serum level of IL-4and IFN-γ and PRRS antibody titre, tissue level of SIgA, IL-4and IFN-γ in jejunum, and tissue level of IL-4and IFN-γ in spleen were tested after slaughtering as well. The results showed that jejunum level of IFN-γ in T2group of growing pigs was significantly lower than which in T1group (P<0.05). Serum level of IFN-γ in T1and T2groups of growing pigs were significantly higher (P<0.05) than which in control group. Jejunum level of IL-4in T2group of growing pigs tended to decrease (P=0.07) comparing to control group. Spleen level of IL-4in T2group of growing pigs was significantly lower (P<0.05) than which in control group. Serum level of IL-4in T1and T2groups of growing pigs tended to increase (P=0.05). Liver index in T2group of finishing pigs significantly lower than that in control group (P<0.05). Spleen level of IFN-γ in T1 (P<0.05) and T2(P<0.01) groups of finishing pigs were significantly lower than which in control group, while serum level of IL-4in all treatment groups of finishing pigs were significantly higher (P<0.05) than that in control group. These indicated that dietary YC could enhance humoral immunity and cytoimmunity in certain degree, and be benefit to health of G-F pigs in summer.