So if she is on 24/7 pasture and I feed her my own mix of alfalfa pellets, flax seed, and racehorse oats...
How much hay should she get?
Should I mix the feed all together into a big bin? or keep it seperate and mix before feed time in a feed bucket?
I guess mixing it in a feed bucket would be ideal because I could mix different amounts of each thing.
Speaking of which... How much of each different grain should she get?
Should I buy some sort of mineral/vitamin supplement? In my Valley Vet Supply catalog I saw "Maxum Crumbles". The description says: A concentrated formula of 32 vitamins, minerals, amino acids and electrolytes that may be lacking in the horse's regular diet. Feed 1-2oz daily. It comes in "crumbles". Does that sounds like a good thing to mix into her feed?
You want to start supplementing hay as your pasture grass dies out or is eaten down. If it's shorter than 3" high, then it's not providing much "food" for your mare. If you're feeding square bales of grass hay (50-60 lbs each) you'll typically want to feed 20-30 lbs a day, or 1/2 a bale. If you have some grass left, you can start with 1/4 bale. Feed hay at least twice a day.
I keep my feed separated, then mix at feed time. "Dry" feeds don't always stay mixed well, which is one reason sweet feeds have so much molasses in them.
Buy a 2qt or 3qt feed scoop that has quart measurement lines inside, so you can see exactly how much you're feeding. If she's an easy keeper (is a bit pudgy), I would go with 1 qt of each alfalfa pellets and oats, with 1/4 cup of flax meal. If she starts to get fat, reduce the alfalfa pellets to 1/2 qt.
If she's not pudgy and you'll be riding her at least 3 days a week, I would feed 2 qts of alfalfa pellets, 1 qt of oats, and 1/2 cup of flax meal. You want to adjust the amounts of each if you notice her gaining or losing weight.
For a vitamin supplement, I really like GrandVite. Valley Vet should have it. It's a powder, but most horses seem to like it. Another good one is Select II, which is pelleted. Maxum Crumbles don't really have that high of values for their ingredients. You don't get as much "bang for your buck."
Two other good ones are SmartPak's SmartVite Maintanence Grass and Uckele's Equi-Base Grass, both of which come in powder and pelleted form.