The intestine is an essential compartment of the gastrointestinal tract (GIT). It is a major site of digestion, nutrient absorption and hydro-mineral exchange homeostasis, harbouring a complex microbiota and a highly evolved mucosal immune system. Interactively, all these aspects of GIT physiology, microbiology and immunology contribute to the so-called “gut health balance”.<br/><br/>Weaning places piglets in a high risk situation. The pigs’ gut health balance is challenged by the different stress factors, including separation from the sow and an abrupt change from milk to a diet based on cereals. Consequently, the young animals become susceptible to infections by different pathogens, which may lead to post weaning diarrhoea (PWD).<br/><br/>The challenge is to protect young pigs from developing PWD without using antibiotics as growth promoters, especially since the practice is banned in Europe(Casewell et al., 2003). Changing the composition of the weaners diet, including the addition of probiotic, prebiotic, or phytobiotic improve growth performance, resistance to diarrhoea and sometimes manipulate the composition of the microbiota and its metabolic activities (Pierce et al., 2005; Kommera et al., 2006; Canibe and Jensen, 2007; Konstantinov et al., 2008)(Pierce et al., 2005; Canibe and Jensen, 2007; Canibe et al., 2007; Molbak et al., 2007).<br/><br/>Whey permeate, especially its lactose content, is one of the alternative nutrient sources which benefit piglets (Pierce et al., 2006). The first part of this thesis tried to answer the hypothesis that the lactose content in whey permeate improves growth performance in piglets after weaning without disturbing the gut health homeostasis. Analyses on gut samples including microscopic observations on the mucosa layer morphology, measurements of short chain fatty acids contents and composition of microbiota communities indicated that post weaned piglets indeed are capable of metabolizing lactose and maintain gut health. These observations were confirmed by improved conversion rate of feed to average daily gain even at inclusion of low level of whey permeate.<br/><br/>Concurrently, addition of probiotic seems to help to balance the gut microbiota, limit the colonisation of coliform bacteria, which may help to prevent severe PWD in piglets (Taras et al., 2006; Konstantinov et al., 2008). However, the responses of piglets to probiotic treatment are strain dependent and often inconsistent (Simon. 2010; Kenny et al., 2011). It would be ideal to obtain selected strains which not only show potential as probiotic for piglet application, but also are capable to proliferate in whey permeate. The second and third parts of this thesis were performed to elucidate these questions (1) whether whey permeate can be used as a medium to proliferate selected lactic acid bacteria which show potential as probiotics and (2) whether selected lactic acid bacteria, when added as inoculum to ferment whey permeate, reduce PWD in infected piglets.<br/><br/>Probiotic selections for pig applications follow similar recommendations available for the human application (FAO/WHO, 2001). We found that only few lactic acid bacteria are able to proliferate in whey permeate without supplementations and maintain their probiotic potential. Our final selections consist of 3 Lactobacillus plantarum isolates, 1 L. rhamonsus isolate and 2 isolates from the genus Weissella.<br/><br/>One of the L. plantarum isolates (L. plantarum 65) and 1 isolate from the genus Weissella (W. viridescens 19) were used as inoculums to ferment whey permeate. The fermented whey permeate product was mixed with basal weaners diets and fed to piglets challenged with E. coli F4. The infection model helped us to identify the potential of the fermented product to minimize diarrhoea from post weaned piglets. Our experiments confirmed that fermenting whey permeate with the potential probiotic W. viridescens reduced diarrhoea frequency, improved feed intake and production of butyric acid in colon and at the same time increased the abundance of Firmicutes in colon.<br/><br/>Post weaning diarrhoea is a global challenge to the pork industry. In China, one of practices to prevent and cure PWD is by the addition of phytobiotics (Kong et al., 2007; Ding et al., 2011). (Kong et al., 2007; Ding et al., 2011)The last part of the project dealt with evaluation of Chinese Herbal Medicine, in the form of Fructus mume and Ziziphi spinosa semen ethanolic extracts, in inhibiting PWD-relevant E. coli F4 and measuring how these extracts regulate innate immune responses in vitro. The experiments revealed that indeed extracts of Fructus mume, and its mixture with Ziziphi spinosa semen, are bactericidal against E. coli F4. Furthermore, measurements of cytokine expressions on intestinal porcine epithelial cell line (IPEC-J2) revealed that Fructus mume regulates immune response by down regulating IL-18 and TNF-α and by upregulating TLR-4.<br/><br/>In conclusion, the works in the present thesis provides knowledge that fermenting whey permeate with a selected probiotic may be an economical yet efficient approach in reducing diarrhoea and helping post weaned piglets to regain their health gut balance. Furthermore, application of Fructus mume may also be another alternative for PWD management. However, an in vivo study to confirm the efficacy in pigs is required.