I think I have seen this before...did it mention how much oats they were feeding to begin with?
My horses get - and yes they are spoiled - Genesis Organic Oats. Genesis Certified Organic Horse Feed
I am trying to get my horses off commercial feeds.
BUUUUT, they only get a 1/4 of a cup a day - and that's only if they are around the barn when I am out dealing with my milk bottle fed calf!