How? My aunt has a cow(a single one) that lives next to her house, has access to a pasture nearby, and by literally any definition you could pick it lives as happy life as a cow can do(unless you subscribe to the idea that no animals should be ever kept by humans, but I am not convinced that would lead to a measurably better life for the cow). It produces a lot of milk that my aunt uses for herself and her neighbours take some of it as well. How is that not "ethical consumption of cow milk"?
I'm definitely not a farmer, but it is my understanding that for a cow to keep giving milk, it needs to give birth once a year. You cannot keep all those calves around, so they go to the slaughterhouse. That means that in an indirect way, the production of cow milk forces calves to be slaughtered.
It depends on where you place things on the moral scale.
For example for the cow to lactate, it needs to be inseminated. Every 4 years I think. When the calf is born it's taken away from the mother. Does a cow mother suffer emotionally from having their baby taken away?
Cows are sociable animals so a single cow would probably feel lonely?
I don't have the answers. It seems like research uncovers more and more human-like emotions associated to animals so it doesn't seem completely out of question. Humans also have a tendency to objectify things so they can shut off empathy.
There is a rare practice where you (for example) separate them just for the night and milk the cow in the morning. During the day, the calf will take the milk. Yes, you lose a lot of the milk that way, but apparently your vet bill also goes down because the calf will be healthier.
Another option is to pool several calves to one cow and foster them for more natural suckling behaviour. This is a bit more common.
Interestingly, apparently cows can choose to either give the milk or not which makes the logistics more complicated.
I can currently only find sources in German for this though ('muttergebundene Kälberaufzucht' / 'ammengebundene Kälberaufzucht').
