Fetal gender influences the quantity of milk produced by cows during lactation, according to a study co-authored by Human Evolutionary Biology assistant professor Katie J. Hinde and Kansas State University associate professor Barry J. Bradford. In the paper, published Monday on the open access journal PLOS One, Hinde and Bradford demonstrate that cows bearing female rather than male offspring produce higher quantities of milk.

The paper—which draws on both Bradford’s specialty in dairy nutrition and Hinde’s expertise in evolutionary biology—focused on dairy farms, one of America’s longest running industries. Yet the collaboration itself was born out of a distinctly 21st century communication.

Just over a year ago Hinde tweeted a blog post about differences in breast milk synthesized for male and female offspring. Weeks later, she received a direct message on Twitter from dairy nutritionist Bradford, who invited her to collaborate on a project that examined the relationship between fetal sex and milk synthesis in cows. After a cursory online search, Hinde joined forces with Bradford.

“The blog is really what started the research project,” Hinde said. “I got the direct message, and of course I Google searched for him, and he was legitimate, so I instantly said yeah, okay.”

Since calves are removed from their mothers immediately after birth, any difference in milk production cannot be attributed to behavioral interactions or postnatal “biased” milk synthesis. Instead, Hinde and Bradford’s finding posits a prenatal bias—one that occurs during pregnancy—in milk production for different genders.

“I suspected this was the case because functional development of the mammary gland actually happens during pregnancy,” Hinde said.

Hinde and Bradford analyzed years' worth of data from the Dairy Records Office, noting that the milk differed in quantity but not quality or composition. Moreover, since cows continue to lactate during their next pregnancies, cows that carry female calves in either their first or second pregnancy are likely to produce a higher volume of milk than cows carrying only males.

Since the dairy industry already employs “sexed semen” to artificially inseminate cows, this study could have economic implications for the efficient production of milk. The report also raises questions about why female fetuses cause increased milk synthesis from an evolutionary perspective. Should further research suggest similar gender biases in milk production for humans, the findings could alter neonatal intensive care unit nutritional recommendations, milk donor matching, and infant formula for boys and girls.

“The most exciting science happens at the margins of fields, where they intersect,” Hinde said. “We know systematically that the greater the diversity of minds addressing a problem the more that research endeavor is improved.”

—Staff writer Jessica A. Barzilay can be reached at jessica.barzilay@thecrimson.com. Follow her on Twitter @jessicabarzilay.