Just like people have different metabolisms, so do horses. What works wonderfully on one horse can be a dismal failure on another.
What they all have in common is to keep the sugars and starches of the entire diet as low as possible. That means 99% of them get nothing but grass hay; some are ok with pasture time and a grazing muzzle, others are not.
Some can have a bit of alfalfa cubes mixed in while alfalfa is "founder in five minutes" for the next horse. My EMS horse gets one pound of timothy/alfalfa cubes and thrives on it BUT he is 25 and needs that extra protein/amino acids for his muscle health.
My IR horse is so founder sensitive, he isn't even allowed to smell the alfalfa cubes. I am such an anal idiot that I turn my back to him as I pass his stall with the soaked alfalfa cubes, to give to my 25 yr old. Once in awhile I even tell him not to breath
You do need to stay on top of your horse's hooves. For some reason, metabolic hooves tend to grow faster than normal hooves. My horses are trimmed every four weeks - everyone is barefoot - the foundered horse has been going out to pasture, since last March, wearing boots and Lily pads - every stinkin' rotten day. I wash those d**n boots with warm water and Dawn Dish soap every night to help prevent any hoof issues. The boots/pads don't go on his hooves until I have throughly picked & brushed them.
I mention the boots as that could be a solution in helping with the sore hooves but, only if someone is willing to learn how to properly put them on, then take them off every night. EasyCare's boots can't be left on more than 12 hours; my horse is out 8 - 10 hours every day then in a stall with 12 inches of limestone crush, grid mats, shavings on top of that.
If you decide on boots, PLEASE have a professional trimmer (or your vet) help size the horse. I would have messed up royally if I'd tried to figure that out by myself. Not only the wrong size boots but the wrong style for his hoof shape.
I know we are all throwing a lot at you, you may want to start a folder on your PC for all this information. Either save the link to this thread to it or copy/paste things into a word document, then save them. You can always print stuff off and use it for your bedtime reading - lol lol lol
I'm chuckling at that but the issue itself isn't funny. My 25 yo was diagnosed with EMS in May, 2007. I did not ride one time that year as I spent the rest of that year in front of this miserable computer researching until my eyeballs looked like road maps to anywhere the car needed an oil change after it got there
We are all trying to help save you some of that initial stress and at least point you in the right directions.
www.ecirhorse.com is one of them that would be beneficial to you
Mill Creek Veterinary Service - Fort Collins, CO talks about Equine Metabolic Syndrome, a/k/a Peripheral Cushings although I never did understand that comparison