AbstractThe objective of this thesis was to study whether the incorporation of fibrous ingredients in the diet of piglets would minimize the intestinal disorders that usually occur during the early period after weaning and facilitate the adaptation of the digestive system of the animals in the subsequent growing periods. To achieve this goal, four trials (chapters 4 to 7) were designed.
In Trial 1 (Molist et al., 2009a), we first wanted to confirm some preliminary positive results associated with a higher growth rate of the animals obtained when an insoluble fibre source (wheat bran, WB) was introduced in post-weaning diets. At the same time, we wanted to assess whether this type of fibre source was appropiate for this period, or whether it would be more advantageous to incorporate a soluble fibre source (such as the sugar beet pulp, SBP). The study aimed to explore the effects of including two fibre sources (WB, insoluble and SBP, soluble) on the performance, the physicochemical properties of digesta and the metabolic activity and composition of the intestinal microbiota. Results showed that intestinal fermentation was low during the first week after weaning. The addition of WB or WB plus SBP in the diet increased intestinal fermentation and the concentration of butyric acid in the caecum digesta, and reduced the enterobacteria population in faeces. It was concluded that consumption of an insoluble fibre source during the first days after weaning (either WB or WB-SBP) modifies the physicochemical properties of digesta and affects the microbial colonization in the hindgut. We also speculated that the effects observed with the inclusion of WB could be associated with: 1.- changes in the physicochemical properties of digesta, such as the higher water retention capacity (WRC) and fermentation promoted in digesta, 2.- a physical effect related to its larger particle size or 3.- a reduction in the transit time of digesta.
In Trial 2 (Molist et al., 2009b), we wanted to confirm the referred reduction of the enterobacteria population promoted by WB, and its likely ability to reduce digestive disturbances after an experimental infection with E. coli K88. In addition, we wanted to clarify whether this effect of WB was related to its particle size. The results confirmed that WB inclusion reduced the
E. coli population in the ileum digesta and, more interesting, also reduced the E. coli K88 attachment to the ileum mucosa. Coarse particle size reduced the microbial diversity compared to finely milled WB.
The third trial (Trial 3, Molist et al., 2010a) was designed to elucidate whether the positive effects of WB on the intestinal microbiota could be due to an effect of WB on the intestinal transit of the animals. Our hypothesis was that incorporation of WB in the diet could stimulate the intestinal transit and so reduce the intestinal stasis of digesta in the piglets provoked by post-weaning anorexia. In this experiment, WB was compared with a drug used in human medicine to treat diarrhoea that slows the intestinal transit (loperamide). The results again showed the effects of WB on the physicochemical properties of digesta (increasing WRC) and the enhancement of gut fermentation (increasing butyric acid and lowering isoacid concentration associated to gut fermentation). Unexpectedly, loperamide increased the feed intake and animal growth. We suggested that this effect could be associated to its analgesic effect on and opioid activity in the intestinal tract. We were not able to confirm if WB reduced the intestinal transit time or the likely role of the modification of the intestinal transit time in the changes in intestinal microbiota.
The last trial (Trial 4, Molist et al., 2010b) intended to confirm all the previous results (the reduction of enterobacteria population and increasing the butyrate concentration) in a comparison between the incorporation of WB with the inclusion of zinc oxide (ZnO) in the diet. ZnO is a widely used ingredient in post-weaning diets producing antimicrobial effects resembling those of the antibiotic growth promoters (AGP) and therefore opposed to the inclusion of fibre in the diet. In addition, and considering the previous observed effects on the E. coli K88 adhesion to the ileum mucosa, we wanted to clarify whether WB could have a physical role on the blockage of the adhesion of E. coli K88 to the mucosa. The results were quite surprising because a negative interaction between WB and ZnO was observed on the intestinal microbiota, which was associated to the presence of phytates in the diet. These results highlighted the recommendation of incorporating enzymes (phytases) in the post-weaning diets in order to increase the bioavailability of zinc. We also detected a high ability of soluble WB extract to bind E. coli K88 in-vitro, which suggests that part of the positive effects on the intestinal microbiota reported with the WB inclusion were due to its ability to block the adhesion of pathogenic E. coli to the intestinal mucosa.
Results exposed in this thesis, support the strategy of including a moderate amount of fibre (>60 g NDF/kg for pigs between 6 - 12 kg) in the diets of early weaned pigs. Our results show the positive effects of including an insoluble source, such as WB on the modification of the intestinal environment and the instauration of a healthy microbiota. These beneficial effects of WB inclusion were associated to changes on the physicochemical properties of digesta (like an increasing WRC of the digesta) and with its ability to block E. coli attachment to the ileum mucosa. However, the presence of phytates in this ingredient may also reduce the availability and efficacy of ZnO in the diet, even when it is provided at therapeutic doses. We propose the consideration of the inclusion of phytase in the post-weaning cereal based diets in order to: 1.- increase Zn biovailability, 2.- maintain the beneficial effects related to ZnO or WB inclusion, or 3.- reduce the therapeutic doses of ZnO in the diet.
|Date of Award||1 Jul 2010|
|Supervisor||Jose Francisco Perez Hernandez (Director)|