If this result is valid, it's probably also true for other mammals that bear young one at a time. If so, it's proabably a lot easier to verify in cows than humans. Less paperwork required for experiments, for one thing.
From the article: "These findings, published in the American Journal of Physical Anthropology in September, echo previous work that showed milk composition varying with infant gender in gray seals and red deer and with infant gender and the mother's condition in rhesus macaques."
