I have not milked a cow out in at least 40 years. As long as the teat is sealed, it is safe from getting infected. Once you open it and remove the waxy seal in it, that quarter can become a target for bacteria to enter. I have had far less mastitis as well as messed up udders since I made the decision to let nature tend to this. Once you start milking a cow out, you better be there to milk her out every day until the calf is able to take all the milk. If you have time to do this, you have far more time on your hands than I do! If a cow's udder is damaged by not milking her out after she calves, she should have been replaced anyways, as you are just producing more daughters that will have similar issues. Another case where Mother Nature knows best!