A dairy cow has been bred to be able to produce enough milk to feed 4 to 5 calves at a time. Only with very careful management might one be able to avoid mastitis, scouring, and other problems. Perhaps other breeds might be more easily successful with only one calf.
Anyone that is new to cattle, and planning on having a milk cow to use the milk, should know that it is not commonly done because it is a large commitment of time and energy. My best friend had one milk cow, and even with a milking machine, the twice daily chore really ties you down, rarely is...