I saw a herd of Beefmaster in Texas a few years ago that really resembled this picture. I think the Beefmaster herd I saw was probably the most uniform herd I have ever seen... anytime,..... anywhere. I was truly amazed as it looked like someone had cloned a cow about a hundred times. The cows were extremely quiet and most would let you walk up to them and scratch them.And their udders were simply amazing. I was truly impressed.
My first guess was South Devon, but after looking for awhile I am thinking that Beefmaster may be a better first guess.