Cow milk is actually meant to be consumed by baby cows. Adult cows do not drink milk. According to the Penn State College of Agricultural Sciences, the majority of calves older than 9 weeks are weaned off their mother's milk; before that point, it is their only source of food.
Most mammals, including cows, lose the ability to digest milk past the age of weaning. That human beings are able to digest dairy into adulthood is an aberration, due to a mutation that is not present in all human populations. An adult cow would not be able to digest cow's milk even if it wanted to drink it.
