My mix ratio is mentioned on the first page... two parts oats (rolled or flatted), one part barley (rolled or flatted), one part BOSS.
The average, healthy, non-working, non-spastic, non-showing 30" Mini would get one cup per day, with two tablespoons of flax and the appropriate amount of vitamin powder depending on your brand. I add some water to get the powder and flax seeds to stick.
The average, healthy, working or self-exercising, or show horse over 31" would get two cups per day with 4 tablespoons of flax with vitamins.
A stallion in breeding season, or a high-strung horse... take out some of the oats and put in more BOSS.
It goes up from there the bigger they are, or if they drive, if they self-exercise a lot, if they show, or if they need to gain weight. The ratio of BOSS and flax would increase in some cases. The most that I have ever fed a Mini was four cups per day, divided into two meals. That was an underweight B-size Mini. For a working or unhealthy A-size, the most I would likely feed would be three cups per day... maybe with an additional cup of BOSS if it was a severely emaciated horse.
I have a dwarf here (about 24") who gets 2 cups per day (one in the morning and one at night) and all the hay he can eat - because he has the metabolism of a chipmunk! It is hard to keep the weight on that little guy, but this amount seems to work great! He stays within five pounds of his target weight and keeps his topline, no matter the season.
I feed a minimum of 1 cup per day, no matter what. I had a Mini come in who was terribly obese (he'd been locked in a stall for at least a year)... however, he still needed all of the nutrition provided by the grain to get healthy. He still got his 1 cup per day, plus his hay rations and has lost over seventy pounds so far, over the past six months. He's got another thirty to go. He was 320 when he arrived and should weigh about 220. We have shipping scales here, so we can tell exactly. He is 31".
I had an emaciated Mini come in four months ago. He was getting three cups of the mix per day (slowly increased up to that amount at first.) He started at 193 pounds, and as of last week, he was 228. He is now where he should be with a nice topline and proportions. He is now maintained on two cups per day (one in the morning and one at night) as he is quite energetic/playful and would likely lose condition on less. He is 31.5".
You can see pictures of these guys in our "Mini Blog" if you go back a little ways.
www.PipsqueakPaddocks.com/available
So, it really depends on the horse and the situation. I mix up each horse's daily ration kind of by instinct (how they are doing, the temperature/weather and what I am asking of them) but based on the above guidelines.
That's what I've been feeding for about five years and it seems to work for us. There are so many opinions on feeding... I just go with what works for me, but I'm always open to new theories/research/ideas. As far as hay, we feed a high quality second or third cut local or orchard grass with up to 20% alfalfa. Timothy is nice too, but I'm allergic to it! LOL