Join Date: Feb 2012
Location: The land of Enchantment
High quality hay is all they need and a mineral block. Giving her oil in liquid form or as small quantities of soy or flax, etc., will cover any fats. When I raised hay - hay, soy or flax was all my horses were fed during warmer months and they were all very healthy and had plenty, plenty of energy. However, for a normal horse w/o any other issues I do not buy into the "any grain is poison" school of thought. Quality and quantity matters in just about everything.
Since she has metabolic concerns, I think the simple hay/oil diet will do just fine. My only concern would be how much and what kind of grass is in the hay for "sugar" content. Either way, you can ensure all the nutrient bases are covered w/o adding sugar/starch w one of the many loose mineral/vitamin products on the market.
There is just as much horse sense as ever, but the horses have most of it.