Some excellent responses so far, Lisa! I especially like the concept of making it so that the horses are 'forced' to eat more slowly. (Google something along the lines of 'hay feeders to slow eating'; I came across a link *somewhere* (can't recall where) about someone who designed several versions of just such hay feeders. I thought I saved it, but can't find it....it was from somewhere overseas, but the principle is very sound...basically, VERY small but secure openings so that the horse literally CAN'T pull out but a few strands at time. I have thought for YEARS that this would work; did some looking for 2"X 2" opening HD wire mesh w/ no luck; just haven't tried again, but intend to, as I think it is one of the BEST answers to extend their eating time and keep them happier throughout the intervals between feedings!
I fed only alfalfa most of my 'horsekeeping' life, including the first several years I had minis. As you did, I realized that if I gave them enough alfalfa to 'satisfy' their need to 'graze', they'd have been grossly obese! They clean up a proper ration of alfalfa in RECORD time, then need something to'do with' their chewing instincts--and that's when trouble begins!
That's when I began buying grass hay, and feeding both kinds. It has been hard to find reliable sources here, also...I've had SEVERAL different sources over the past 18-20 years--just when I got a good source, something would happen so that I couldn't count on it anymore!! At one time we went as far as Taos to pick it up; my husband would make TWO trips to haul what I needed! Recently, I've just had to buy it from the area feed dealers, AND haul and stack it myself.
Grass hay is uniformly higher priced than alfalfa, here---no matter what the type. I had to feed bermuda a time or two, but only to my 'big' mare. I don't care for it, honestly, though I HAVE seen some that was way better than others.
If it's all you can get, examine the quality...does it have a least SOME 'color'? Is it weed and mold free, and NOT dusty(I found that a serious issue...being over dry and full of 'dirt'!) If the blades/stems are REALLY long, to me that means it was overmature when cut--and, I'd consider it more of a 'hazard' to feed, to minis, at least.
I'd be surprised to find bermuda 'overly high' in protein? It is more likely to be early-cut alfalfa, around here at least, that would have that issue. For good info, go to www.safergrass.org(or maybe, .com--not sure)--but it is an EXCELLENT source of info about grasses and hay made from grasses.
If you use it, introduce VERY slowly. You could easily 'rinse', or even soak, the bermuda-- nevermind the protein thing-to 'soften' it, add some 'built-in' moisture, and maybe make it easier to eat.
The highest protein grass hay is 'usually' timothy, but of course, SO much depends on a variety of things about the growing conditions that there can be no 'hard and fast' answers...
I personally like a mainly orchard grass mix, but the main thing is the overall QUALITY of the hay!
Good luck!
Margo