Mothers favor daughters more than sons, a latest study on dairy cows by Kansas State University and Harvard University researchers states.
For the study, the researchers analyzed the 2.39 million lactation records from 1.49 million dairy cows. Cows produced significantly more milk for daughters than for sons across lactation, said Barry Bradford, associate professor in K-State's Department of Animal Sciences and Industry, in a press release
"Our results provide the first direct evidence that the sex of a gestating fetus can influence milk production," Bradford said. "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."
The researchers also found that sex of the fetus a cow carries influences the milk production during an established lactation.
The authors said that the study results can also show the implications for humans. "Among the surprises in this study was the fact that the bias was in favor of daughters rather than sons, as some evolutionary hypotheses have predicted. Daughters seemed to have the most dramatic effect on the initial development of the mammary gland, because the bias against sons was greatest in the first lactation," Bradford said.
The study results also showed that fat and protein percent in milk did not alter in cows that gestated a son or daughter. This means the milk quality remained same but just that mother cows fed their daughter cows more. This was because the total amount of milk fat and protein after gestating a daughter were higher than after gestating a son.