A team of researchers from Harvard University, Kansas State University and Dairy Records Management Systems have published a new study in the journal PLOS ONE that shows that bearing a female calf brings udder fulfillment to a dairy cow -- a find that could be a valuable piece of information for the $140 billion-a-year U.S. dairy industry.
“Cows favor daughters, producing significantly more milk for daughters than for sons across lactation,” the researchers wrote in the journal.
The increased production was biggest when a cow’s first calf was a daughter, and highest when a mother cow produced two female calves in succession. Cows that had back-to-back daughters produced as much as 1,000 pounds more milk more than cows saddled with two sons.
"If this were adopted by the dairy industry today, not counting the cost of the technology for sperm selection, the growth in terms of wholesale milk value is in the ballpark of $200 million gross, just by manipulating the conception of a daughter on the first pregnancy," lead author and Harvard University researcher Katie Hinde said in a statement.
Researchers have developed two possibilities to explain why a cow would produce more milk for a daughter than or a son, especially given that male calves are typically larger. One idea is that favoring daughters with more milk is an evolutionary adaptation, optimized to get daughters developing earlier and reproducing faster. Another possible explanation is that the estrogens produced by the developing female calf in utero are boosting the hormonal signals that dominate the mother’s milk production.
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