In the 16th and 17th centuries, cattle breeds were as different from modern cattle as poultry breeds are. Devon cattle were among the breeds that the maids may well have been milking.
The American Milking Devon was developed from the breed named for the county Devon in England. It retains good production in milk as well as meat. This Devon heifer, "Fashion 5th," is an illustration from Livestock and Complete Stock Doctor: A Cyclopedia, by Jonathan Periam and A. H. Baker, published in 1910. The breed is known for its fast walking, which allows it to cover fields efficiently. It is a desirable breed for oxen as well as food production.
The Milking Shorthorn, which traces its history back at least to the estates of the nobility of Northumberland in England of those days, would also be a candidate for the hands of those maids.
Significant points for good dairy cows, according to the Stock Doctor, are: "... a small neck, sharp shoulders, small brisket and small bone. Moreover, small bone usually accompanies thrift, and is universally found in improved breeds."
Milkmaids are associated with good skin at this period of time. Because of their close association with cows, they often acquired cowpox, a much less serious disease that conferred immunity to small pox on them. Thus their skin was not marked by the scars of this terrible disease. The term 'vaccine' comes from the Latin word for cow. Edward Jenner relied on this observation to develop the first vaccine, http://www.jennermuseum.com/sv/smallpox2.shtml.