There would be no milk left for anyone to drink. Again, murder is murder. Mothers milk is for baby animals. Hope this clarifies things for you. The scenario about the hen being used for food when it becomes too old to lay is invalid.
Murder is murder.
Similarly, the calf who is weaned by hand, and who shares its mother's milk is not treated as a veal calf. In a natural situation, ie when a calf is weaned, mother's milk dries up. There would be no milk left for anyone to drink. Again, murder is murder. Mothers milk is for baby animals.