I don't know of any good equine vets around Brookings or Watertown. I drive 120 miles to Sand Creek Vet which is Dr Dave Schultz. He's south of Huron 15 miles.
I use Bill Ouverson in Madison at the Lake Vet Clinic. Or you can try the Twin Lakes Clinic, in Madison and use Brooke Braskamp, her family is very horse oriented