The inventions described herein relate generally to the use of compositions to increase output of acetate and lactate while reducing pH and the levels of pathogenic bacteria and inflammation in the gut of a nursing infant mammal including humans. These compositions generally comprise one or more bacterial strains selected for their growth on mammalian milk oligosaccharides, a source of mammalian milk oligosaccharides, and, optionally, nutritive components required for the growth of that infant mammal.