Here's why:
* Lactation is a biological process tied to pregnancy and childbirth: Milk production (lactation) is triggered by the hormones released during pregnancy and the act of giving birth. These hormones stimulate the development of the mammary glands and the production of milk.
* Hormonal triggers: The hormone prolactin, responsible for milk production, increases significantly during pregnancy and peaks after birth. This is why cows, like other mammals, begin producing milk soon after giving birth.
* Natural selection: This biological design ensures that the newborn calf has access to a vital source of nourishment.
While cows can be milked even after their calves are weaned, they won't naturally produce milk without having a calf.