It gives over five gallons of milk daily. Its sweet milk is enjoyed by children and grown-ups alike. People who can't drink milk turn it into yogurt and eat it instead.
(From Bulbapedia) Miltank is a bipedal, bovine Pokémon, which can only be female. Its body is mostly pink, with a yellow belly and black, angular markings along its back. A black hood-like marking surrounds its face with a pink, triangular mark on its forehead. There are two small horns on top of its head. It has large, blue eyes, a black nose, and a wide mouth, as well as long, black, floppy ears with yellow insides. Miltank has a yellow udder with four pink teats. All four of its limbs end in black, cloven hooves, and its long tail is tipped with a black sphere. In SM070, a smaller Miltank was shown without any horns or teats, implying that this is what young Miltank look like.
Until Generation VI, Miltank was the only known Pokémon that could learn Milk Drink. The milk that it produces is sweet and very nutritious, and can be used to heal Pokémon and ill or weary humans. The taste and nutrition of its milk improves with the quality of the pastures it lives in. It can produce over five gallons of milk per day, which in turn can be turned into yogurt or enjoyed unchanged by children and adults alike. Miltank lives in grasslands, and is also raised on farms.