Does any human culture routinely do this? Typically taboos have some evolutionary basis. So what would that be? Does any mammal drink the milk of its own species, besides nursing?
Giving a woman food for her to inefficiently convert to different food is a waste of time and energy; it only makes sense for infants that can't eat much else (and even there, plenty of people find substitutes so the woman can get back to work).
Turning grass, which people can't eat, into a food people can eat makes a whole lot more sense.