Animal Mothers Customize Breast Milk Content And Quantity Based On Offspring Gender
Animals produce different breast milk depending on the gender of the their offspring, according to a study by evolutionary biologist Katie Hinde of Harvard University. Analyzing the breast milk of rhesus monkeys and the lactation records of 1.5 million cows, Hinde found that offspring gender accounted for noticeable differences in both the content of the breast milk and the amount produced. The findings were published earlier this month in PLoS One.
Like Us on Facebook
"There is this prevailing myth that mother's milk is standard," Hinde said on Friday at the annual meeting of the American Association for the Advancement of Science. However, as Hinde told Discovery News, "There's evidence that mothers are producing different biological recipes of milk for sons and daughters and the magnitude of this effect varies across their reproductive careers."
In rhesus monkeys, male babies received breast milk richer in fat, especially when they were the firstborn, Hinde found. But female babies got more breast milk, which also had a higher amount of calcium than males' milk. Hinde speculates that a greater amount of breast milk is given to daughters to accelerate their development, so that they can begin reproducing at an early age. (Female rhesus monkeys reach sexual maturity earlier than males do.)
Hinde then looked at the lactation records of Holstein cows. Unlike rhesus monkeys, calves are separated from their mothers shortly after birth, so cow lactation records would allow Hinde to determine whether breast milk begins to change prenatally. The lactation records of 1.5 million cows suggested that this does in fact happen before birth. When cows had daughters, they produced 1.6 percent more milk; if cows had back-to-back daughters, they produced about 980 pounds more milk than when they gave birth to two sons in a row.
As with rhesus monkeys, cows may give female offspring more milk because daughters mature earlier than males, so they need the boost that comes with extra milk. Bulls reproduce later and don't need as much milk early on. "[M]others may be able 'under-invest' in a son with relatively less consequence for the number of offspring he will go on to sire," Hinde told National Geographic.
"Our results provide the first direct evidence that the sex of a gestating fetus can influence milk production," said study co-author Barry Bradford, an associate professor in Kansas State University's Department of Animal Sciences and Industry. "One possible explanation is that a daughter is able to let her mom know, in advance, that she expects to receive more milk than her brothers."
And what about us humans, you may be wondering? Bradford says that there hasn't yet been a study to systematically analyze composition and yield of human milk based on gender. While there has been some research suggesting that nutrients vary depending on offspring's sex, no study has measured human milk volume in relation to gender.
Despite the lack of such a study, Hinde says that we should start considering whether baby formulas should take gender into account.
"Right now, formulas are the same for sons and daughters, and recommendations for neonatal intensive care units are the same," said Hinde. "We make different deodorants for men and women but we're not thinking about whether the developmental needs of daughters and sons are identical."
© 2012 iScience Times All rights reserved. Do not reproduce without permission.