you've gotten a lot of replies regarding the lives of milk cows and how they're bred - one other factor athat I didn't see mentioned is that only about half of the calves turn into dairy oows, and the world has very little use for living bulls.

The same issues arise in chicken farming, where it's impossible to have eggs or dairy without death.

I saw some image of genetically modified eggs where they supposedly were able to control the sex of the chickens pre-birth, but in general, you need to kill about half of the animals born.