Draft horse:

A draft horse (US), draught horse (UK) or dray horse (from the Old English dragan meaning to draw or haul; compare Dutch dragen and German tragen meaning 'to carry'), less often called a work horse or heavy horse, is a large horse bred for hard heavy tasks such as ploughing and farm labor. There are a number of breeds, with varying characteristics but all share common traits of strength, patience, and a docile temperament which made them indispensable to generations of pre-industrial farmers.

Source:Wikipedia