Surprise mother’s milk find

A SPECIAL blend of mother’s milk just for girls? New research shows animal mothers are customising their milk in surprising ways depending on whether they have a boy or a girl.

The studies raise questions for human babies, too – about how to choose the donor milk that’s used for hospitalised premature babies, or whether we should explore gender-specific infant formula.

‘‘ There’s been this myth that mother’s milk is pretty standard,’’ said Harvard University evolutionary biologist Katie Hinde, whose research suggests that’s far from true in monkeys and cows.

Instead, ‘‘the biological recipes for sons and daughters may be different,’’ she told the American Association for the Advancement of Science.

Paediatricians have long stressed that breast milk is best when it comes to baby’s first food. Breastfed infants are healthier, suffering fewer illnesses during the first year of life and less likely to develop asthma or obesity later on.

But as this research is difficult to conduct in people there have been few studies of the content of human breast milk, and how it varies from one birth to the next or even over the course of one baby’s growth.

Hinde found that the milk rhesus monkey mothers produce is richer in fat when they have male babies, especially for a first birth.

And, they made a lot more milk when they had daughters.

She paired with Kansas State University researchers to examine lactation records of nearly 1.5 million Holstein cows.

Sure enough, cows that bore heifers produced about 1.6 percent more milk. More interestingly, those that bore a second heifer in a row produced almost 450kg more milk over nearly two years.

Hinde also found milk produced for female monkeys contains more calcium. One explanation: female monkey skeletons mature faster than those of males, suggesting they need a bigger infusion of this bone-strengthening mineral.

Human girls’ skeletons mature faster than those of boys, too, but there haven’t been similar studies of calcium in human milk, Hinde said, and she wondered whether premature babies in intensive care might fare better with gendermatched donor milk.