Where are you located and how thick is her winter coat? My Percherons look like yaks during the winter and sweat anytime the temp gets near 60 (like yesterday). Great resource for draft nutrition is Dr. Beth Valentine's book http://www.amazon
.com/Draft-Horses-Owners-Beth-Valentine/dp/1893707121/ref=sr_1_1?ie=UTF8&qid=1326081402&sr=8-1. Unless you are feeding huge amounts of the cubes, I would be surprised if that was the problem.