This does not make sense. Why would a cow make milk only while pregnant? So as soon as the calf is born no more milk? I'd expect lactation to occur after birth.

This does not make sense. Why would a cow make milk only while pregnant? So as soon as the calf is born no more milk? I'd expect lactation to occur after birth. A cursory internet search suggests the cycle is pregnancy (9 months), birth, milk production of various duration, 2 months of "drying off" and then on to the next pregnancy. How different is that from what occurs in nature? Don't most animals get pregnant every year during the fertile period of their life? Only unnatural part of this is separation of calf and mother as well as other details like diet. If you're concerned with that you can source your milk from responsible dairy farms, the problem there being that most people value cost savings over humanitarian concerns. Also note that 20% (according to some random source) of beef production comes from former dairy cows. If you consider meat a byproduct of cow milk then cow milk is saving us from some of the environmental impact of beef production. (FWIW I don't drink animal milk.)