Effects of dietary caprine milk oligosaccharides enriched fraction on maternal large intestine and the consequences for the development of the offspring : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy, Massey University, Palmerston North, New Zealand

Abstract

The colonisation of the neonate gastrointestinal tract by health-promoting microbiota is likely to improve the overall health of the infant and may also have health benefits in later life. Initial development and maturation of the foetal/neonatal gastrointestinal tract is heavily influenced by the in utero environment which itself, may be altered by the maternal diet and gastrointestinal tract microbiota composition. The maternal gastrointestinal tract microbiota can be altered by supplementation with synthetic oligosaccharides; however, positive effects on the health and well-being of the offspring have not been adequately established. Human milk contains natural oligosaccharides known to improve the gastrointestinal tract colonisation and the development and maturation of the infant gastrointestinal tract. Among domestic farm animals, caprine milk has oligosaccharides structurally similar to human milk and potentially similar beneficial effects for the infant. We hypothesised that feeding caprine milk oligosaccharide enriched product to pregnant and lactating mice would induce changes in the maternal large intestine microbiota and milk composition, accelerating the development and maturation of the offspring’s large intestine tissue and altering the gastrointestinal tract microbiota composition. The aim of this project was to obtain bifidobacteria from the faeces of breast-fed human infants and determine which were of capable fermenting caprine milk oligosaccharide enriched product. Subsequently, the effects of the best strains on the morphology and metabolic pathways of the colonic mucosa of germ-free and conventionally raised mice, supplemented with dietary caprine milk oligosaccharide enriched product. The present study is the first to report New Zealand Saanen caprine colostrum, milk and whey. An enrichment method previously described was used to produce a caprine milk oligosaccharide enriched product for in vitro and in vivo assessment of its health effects. Caprine milk oligosaccharide enriched product was shown to differentially stimulate the growth of bifidobacteria, commonly found in the gastrointestinal tract of breast-fed infants. Among the bifidobacterial species tested, Bifidobacterium bifidum utilised caprine milk oligosaccharide enriched product most efficiently when compared to Bifidobacterium breve and Bifidobacterium longum subsp. longum. B. bifidum (AGR2166) was shown to ferment the sialyloligosaccharides, 3’- and 6’-sialyl-lactose present in caprine milk oligosaccharide enriched product through cell-associated sialidase expression. Augmented microbial biomass associated with enhanced growth and in vitro fermentation of caprine milk oligosaccharide enriched product, increased the production of microbial fermentation end products such as acetate and lactate. These findings indicate that in vivo caprine milk oligosaccharide enriched product may stimulate the growth and fermentation of bifidobacteria within the gastrointestinal tract. Germ-free mice or mice mono-associated with B. bifidum (AGR2166) were used to test the in vivo effects of maternal caprine milk oligosaccharide enriched product consumption during pregnancy and the effects on the foetus. Caprine milk oligosaccharide enriched product diet showed no effects on maternal gastrointestinal tract or foetal growth regardless of microbial status. Mice inoculated with B. bifidum (AGR2166) and fed caprine milk oligosaccharide enriched product diet, however, showed an increased bacterial translocation from maternal gastrointestinal tract to organs and placenta (inferred by the presence of the bifidobacteria 16S rRNA gene in the maternal organs). Increased translocation of commensal bacteria from maternal gastrointestinal tract to the foetus may have important effects on foetal immunological programming. The consumption of caprine milk oligosaccharide enriched product, during gestation and lactation were also tested in conventional rodents and it had no effects on maternal gastrointestinal tract microbiota and morphology. Changes on maternal lipid metabolism and increased maternal milk protein, however, were observed. These modifications may have positively affected the development of the pups, relative abundance of gastrointestinal tract bifidobacteria and butyric acid production at weaning. Important changes in the plasma and urine metabolites involved in bile acid and fatty acid metabolism were also observed in the pups as a consequence of maternal caprine milk oligosaccharide-enriched diet. The effects of maternal caprine milk oligosaccharide enriched product diet on pups, were no longer apparent after 30 days of consuming a control diet post-weaning, however, detrimental physiological characteristics such as an increased body fat were observed. Further studies, are needed to understand the physiological effects of caprine milk oligosaccharides on the maternal/infant pair.