I have a pony, he is 19yo, got him when he was 12 and I was 7. Anyways, we had problems with his food when we first got him and he went stiff in his front legs, its called lamenitis, and you have to try to maintain a healthy weight and don't FEED ALFALFA! Alfalfa is way too rich for them and it can cause them to founder or go lame. Not good. We feed a hay called teff and we havent had any feet issues since we switched. So I would reccomed switching him and for the soreness, let him lay down and rest it, don't do any major riding until he has gone at least a week or two with out limping just make sure he is moving enough so he is not at risk of colic.