How much alfalfa are they getting? Is Marco timid? If so, how timid? Given the history you've outlined, the only thing I can think of is complications due to the possible polio, or he is being pushed away from the feeder and can't eat.
If he were mine, I would 1) get him in his own pen or out of there asap! I know you're trying and I'm not suggesting in any way that you're not. Unfortunately, **** happens. 2) get a bale of good quality hay (at this point - probably grass. Given his condition, I'm afraid his system couldn't handle the alfalfa and he would start scouring.) divvy up 2, maybe 3 flakes into large grocery bags, feed bags, tubs, whatever I had and take it with me when I went out to give them their grain and pellets. I would also take a large stick - I've found a 3/4" solid wooden dowel about 4 to 5' long is pretty effective in most cases, a firm tap across the chest or across the butt should get the point across very nicely - and make sure that Marco got however much he wanted. If you can take him out of his current pen to feed him, that's even better! Let him eat a good amount of the hay, then give him the other stuff and offer more hay. Just go kinda slow at first so his system doesn't get overwhelmed and cause more problems than you're already dealing with. This whole situation has got to be so frustrating for you. I'm sorry, and I hope this helps.They are fed together, I believe three flakes twice a day, that's why I supplement as much as I can
I would stick with the grass until he gets some weight on him, then transition to alfalfa if you want to. It's much easier to avoid health problems than it is to treat them - especially where you are not able to easily treat him should the alfalfa cause diarrhea.Should I just get alphalfa? Or grass hay?