Thanks everyone! I am encouraged that most think his weight is pretty good....I may just be paranoid after seeing him at his worst (think at least 100 lbs. Less when I got him)
I was at the barn today and if I lightly run my hand along his side, I can't feel ribs. I have to press fairly firm to feel them so that is good news. I upped his soaked alfalfa by a pound and will watch him closely to make sure he doesn't lose anymore. I think he is borderline. Hard to work on building muscle in winter as the ground has been frozen for days. I can trailer to an indoor about once a week but we haven't done our hills/trails in a bit.
Do trot poles work the back? We did some of those today.