Intestinal diseases in nursery pigs constitute a risk for development of antimicrobial resistance because of antimicrobials being frequently prescribed as a treatment approach. Beside multiple stressors encountered at the event of weaning, gut microbiota dysbiosis and an immature immune system are
leading causes to the development of post-weaning diarrhea. The neonatal period has been proposed as a time of physiological plasticity, where the consequences of perturbations are development of immune and metabolic related disorders later in life. However, it is also regarded as a window of
opportunity, where programming events allow for shaping an eubiotic gut microbiota with long-term benefit. Considering that immune maturation is directly influenced by the microbes present in the gastro-intestinal tract, it thus seems evident to investigate if supplementation of beneficial microbes
– such as probiotics – during this time window would make the piglet more robust for the event of weaning. Hence, the overall objective of this thesis was to develop a probiotic product for early inoculation to newborn piglets in order to establish a healthy microbiota leading to a long-lasting imprinting, whereby the piglets become less susceptible to enterotoxigenic Escherichia coli (ETEC) post-weaning diarrhea. The project consisted of a rational selection phase of probiotic strains and two animal experiments evaluating the proof of concept.
During the in vitro selection phase, ten probiotic strains were evaluated for their ability to: enhance intestinal epithelial barrier function, reduce adherence of ETEC to intestinal cells, inhibit growth of ETEC, and grow on porcine milk oligosaccharides. Strains included in the screening were of the species Lactobacillus, Enterococcus, Bifidobacterium, Faecalibacterium, and Bacillus. Results showed that all tested probiotics exerted inhibitory properties towards ETEC F18, and that B. longum subsp. infantis was superior in utilizing porcine milk oligosaccharides. Furthermore, E. faecium enhanced intestinal epithelial barrier function to a high extent and seemed to be the best candidate for
competitively excluding ETEC F18 adherence to intestinal epithelial cells. Four of the ten probiotic strains were investigated using an in vitro model simulating the small intestine of suckling piglets. Due to high variation in piglet digesta, it was difficult to identify specific MoAs of the tested probiotics and their potential as a prophylactic measure against ETEC infections in pigs. Based on these in vitro studies, four probiotic strains, complementing each other’s health effect, were selected. Early inoculation of the multi-species probiotic product consisting of L. rhamnosus, E. faecium, B. breve and B. longum subsp. infantis to suckling piglets was investigated in two animal experiments.
The first experiment focused on the effect on the gut microbiota composition and immune responses, and the results showed that oral probiotic inoculation to newborn and suckling piglets altered microbial diversity in intestinal content and tissue as well as in feces on day 35 post-weaning and after cessation of probiotic administration. After weaning, the probiotic inoculated pigs had a higher expression of genes in small intestinal mucosa accounting for local immune responses, whereas the acute phase protein SAA was downregulated. Incidence of diarrhea during the first week after weaning was lower in probiotic administered pigs. The second experiment assessed the effect of early
probiotic inoculation in ETEC F18 challenged weaned piglets. Results showed that pigs supplemented with probiotics early in life and challenged with ETEC F18 post-weaning had fewer days with diarrhea and a significantly reduced number of pigs shedding ETEC F18 and STb toxin in feces compared with the non-probiotic supplemented pigs challenged with ETEC F18. In conclusion, the
results from this project indicate that early probiotic inoculation to suckling piglets drives a long-term immunomodulation through changes in specific microbial antigens leading to higher resilience during challenging situations such as weaning or pathogen challenges.