My Dancer had a really thick, beautiful multi-colored mane. I walked out one day and it was GONE! I think one of the other horses started chewing on it. There are a few chunks left, but mostly it's all new growth.
The grass hay is actually fine - your horse doesn't need any grain unless he's in fairly hard work. We feed plain old prairie hay usually - this year it's orchard grass and brome, with a bit of beet pulp, balanced feed and Omega HorseShine (flax, psyllium, yeasts and other goodies). It really does help the horse's coats look better, and Dancer's mane is growing in pretty quickly. If I can keep the other horses from chewing on it, she should be pretty much back to normal in a few months.
Plain Old Dee, horses Dancer and Rain I believe in dragons, unicorns, good men and other mythical creatures!