'Heavy horses' is the general term used to describe working horses built big enough to pull loads behind them.
Those in my company 'Trojan Heavy Horses' come in all shapes and sizes.
The latest in our stable is this Mountain Ardennes mare from Belguim - seen here at Teagasc's Farmfest 2008 - who is a mere 15 hands high compared to taller breeds we use like English Shires and Scottish Clydesdales. There are two Ardennes breeds with the Lowland Ardennes being bigger that the Mountain Ardennes, which is more compact and suited to hill work.
No less strong, her small stature means she has a smaller angle of draught than taller breeds, so needs less effort to shift the same load as the bigger heavy horse breeds such as the Shires below.
Undertaking a job for the Irish National Forestry Foundation in 2007 on Manch Estate in Dunmanway in West Cork, the ground was so steep it was necessary to hitch two Shires together to shift full length poles of Douglas Fir.