This change begins to occur in late pregnancy with the generation of vast numbers of cells with two nuclei, researchers have said.
Using unique three-dimensional (3-D) imaging technology, they found huge numbers of cells became binucleated (developed a second nucleus) - a process that is critical to milk production.
The process - which lasts only for the duration of lactation - is important for the newborn to thrive when breast milk was the sole nutrient.
"Presumably this is important to avoid mishaps," Visvader said.
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The study showed how mammals, including humans, wallabies and seals, were primed to adapt to pregnancy in ways that best supported the survival of their babies, researchers said.
"Based on their presence in five different species, these findings suggest that this process has evolved in mammals as a mechanism to maximise milk production, which is essential for nourishing the newborn and the survival of mammalian species," said Geoff Lindeman from Walter and Eliza Hall Institute.