promote growth of bifidobacterium in the infant gut. milk microbiota are thought to play an essential role in programming the infant immune system, and tend to reduce the risk of adverse infant health outcomes. differences in milk oligosaccharides between humans and non-human primates could be indicative of variation in pathogen exposure associated with increased sociality and group sizes. together, these observations may indicate that milk microbial communities have coevolved with their human host, supported by the expectation that microbes which promote host health facilitate their own transmission and proliferation. comparisons with other mammals both human and macaque milks contains high abundances of streptococcus and lactobacillus bacteria, but differ in their respective relative abundances of these taxa. bacteria observed to be most common in healthy bovine milk include ralstonia, pseudomonas, sphingomonas, stenotrophomonas, psychrobacter, bradyrhizobium, corynebacterium, pelomonas, staphylococcus, faecalibacterium, lachnospiraceae, propionibacterium, aeribacillus, bacteroides, streptococcus, anaerococcus, lactobacillus, porphyromonas, comamonas, fusobacterium, and enterococcus.