Is there a difference in the value of milk from different cow breeds, because of a difference in the protein produced?

In the commercial milk industry, dairy cows consist of very specialized breeds that can produce very large amounts of milk. Over 90% of dairy cows in the U.S. are black and white Holsteins. After Holsteins, the most common U.S. dairy cows are ...

from The World's Healthiest Foods http://ift.tt/1Fvwi6Y