Fibre fermentation in the pig intestine : effect on metabolite production and nitrogen excretion

Fine tuning a nutritional strategy by incorporating dietary fibre (DF) in pig diets can help to improve gut health. Fermentation of DF, especially the soluble fraction, in pig intestines yields short-chain fatty acids (SCFA) and lactic acid, which have been found to improve gut health by favouring the growth of health-promoting bacteria such as Lactobacilli and Bifidobacteria, at the expense of pathogenic ones like Clostridium or Salmonella, which may enhance the health of host species. The presence of fermentable fibre in the pig diet can also contribute to reducing nitrogen (N) excretion, which can have a positive impact on the environmental footprint, one of the main concerns of a modern commercial pork production. The overall objective of this thesis project was to evaluate the fermentation characteristics of a selection of feedstuffs in the pig intestines and their potential impact on the gut environment and nitrogen excretion. The evaluation was performed by executing two projects using both in vitro and in vivo studies. The first project focused on the fermentation characteristics of hulless barley in comparison to hulled barley and oats and their effects on the gut environment, especially the production of fermentation metabolites. The rate of fibre fermentation in the intestines was first studied by means of an in vitro gas production technique. The results demonstrated that hulless barleys have higher fermentability and produce higher amounts of SCFA than hulled barley and oats. An experiment carried out on pigs confirmed that the fermentation of the soluble fibre fraction of hulless barley in the gut leads to increased production of SCFA and lactic acid, which in turn contribute to the growth of potentially beneficial microbiota and decrease potentially harmful bacteria, an indicator of improved gut health. This finding shows that gut health parameters may be modulated. Thus gut health could potentially be improved through feed formulation by a judicious selection of feed ingredients with specific fibre fractions, not only by the addition of isolated fibres, which is commonly recommended at present. The second project was executed to study the effect of some feedstuffs differing in their DF and protein content on fermentation characteristics and N excretion in pigs. The feedstuffs included wheat bran, wood cellulose, peas, pea hulls, pea inner fibre, sugar beet pulp, flax seed meal and corn distiller's dried grains with solubles. The results showed that peas and pea fibre-based diets produced higher amounts of SCFA and reduced N excreted, compared to others. In a parallel in vitro study, fermentation characteristics and bacterial protein synthesis was also studied using the same feed ingredients. The findings of the in vitro study corraborated the results of the in vivo experiment. These studies showed that peas and pea fibres have the potential to be used in pig diets in order to gain gut health-benefits and reduce N excretion. From this thesis, it can be concluded that sources and type of dietary fibre have a significant effect on the production of fermentation metabolites in the pig intestine and on N excretion. Among the feed ingredients studied, hulless barley and pea fibres seem to have the greatest potential to be included in pig diets as a source of fermentable fibre to modulate the gut environment, which in turn, extend possibly health-promoting properties and reduce N excretion from pigs. However, further research is needed to understand the specific health benefits of these fibre sources and to quantify the specific fibre components required to achieve these benefits