grass I agree with everything until #4 most horses don't need grain for extra calories it is just as easy to use hay pellets or rice bran and much healthier for the horse too
PeggySue - I actually agree with you more than you realize. I saw your post about Ration Balancers, and unless I misunderstood, I realize now that's essentially what I do and believe in. I wasn't really aware of the existence of using a different term to differentiate. I actually very much appreciate being able to make that distinction now.
Based the first three points, good quality hay, great multivitamin/mineral supplement, + high quality pre/probiotic, any 'grain' that is needed would be such a small amount that it is not tough on the horse's system - or one would use a "ration balancer" either unfortified or fortified (which would then replace the vite/min supp), that contains no grain at all. Some horses do fine on a barley/corn/oats mix for some extra calories (but I'm talking more like 1- 2 pounds at the most, not 6-10 - because I agree they are not digestively or metabolically made to eat huge volumes of grain) - but for many as you said its better to use hay pellets or a concentrated ration balancer that does not include grain as it's easier to digest, makes them less 'hot', better for Cushings/potential IR horses, etc.
On another note, I don't like rice bran though. I realize that it's a really popular go to for a lot of people. But I've heard it's one of the most heavily chemicalized crops, and if you think about it, all those chemicals land straight on the hull....so unless you're getting it organic, imo it's just too much pesticide. I used to use it to keep weight on my horse, a few pounds a day. Now he gets just a cup and a third of a great natural concentrated 'ration balancer' fortified with vitamins and minerals to work with his mostly grass hay diet, using whole expelled organic soybeans as the first ingredient (handy to know that term now - as opposed to the blanket statement of fortified feed) and no chemicals. He's in better overall weight, shine, and condition than back in the days when I boosted with rice bran. For what that's worth.
I've become very fascinated with Chia as a concentrated calorie source as well as having as many Omega 3s as flax. The Aztecs made clothes out of flax, and ate chia.