Too much sweat?

I moved Cowboy to a new barn beginning of November and thankfully they have an indoor. I've been able to do allot of riding, but I have one concern.

Cowboy doesn't grow a nice wooly coat in the winter so I do have him blanketed as he shivers at the sight of a raindrop and wind. (bit of a princess.. ) He is deffinitly not concidered out of shape as he has been constantly worked since late April and not over weight (could actually use another 50 lbs IMO..) .

I noticed he sweats really bad this winter! As in I can barely do a warm up (maybe 3-4 laps of jog around the arena) and his chest is sweating! If I do a normal workout with him he is full bodied soaked and have to change 2 coolers on him and come back 2 hours after my ride and he will finally be dry. This summer it took allot for him to sweat but this winter has been unreal! With the new job I won't have the time to be coming down to enjoy a nice ride and then wait for him to be dry.. Is this a sign of something going on with him or decifient in something? Or is this normal for the winter months? It's been a long time since I've been able to ride during the winter so maybe I'm just out of the loop!

Keep in mind this winter has been exceptionally mild.... That would be my guess. Even though he doesn't grow much of a coat, he would still be sort of "expecting" or getting ready for the super cold days.. could definately be a factor.