How long were you gone for? Maybe it's a conditioning issue, was anyone riding him for you? Also, how long has he been there? Maybe he was stressed from the move and the changes to his schedule, new herd situation, different turn out schedule, or potency of pasture, hay, grain, less actual work, and or change in work schedule, etc.
Also, when did he last have his teeth done? Could be there are some dental problems that need to be addressed.
I know its upsetting to see dramatic differences in weight, but also could it be that since you were gone for some time, that you are now looking at him in a different way, more critically? PLUS, I really have to mention the pasture issue again,..., this is the time of year that pasture really begins to drop off, and could be time to start supplementing with grain. Maybe if he wasn't getting worked they didn't want to maintain a grain schedule b/c of tying up/azotoria, or colic/laminites issues.
I'm sure once you speak with the barn manager, you'll feel better. Or at least understand their management practices better.
Don't worry, I'm sure he'll pick back up in NO time

. Redboy
