Vaclav Smil's Millennium Essay “Horse power” presents a good overview of the important role of draught horses in agricultural production in North America during the last century1. Some points worth adding are that mules were another key source of draught power on many farms2, and that the larger draught-horse breeds are, during brief exertions, capable of developing even more than the three horsepower Smil mentions.
Records of draught-horse championship pulling trials in the United States show that a team of two animals could develop 30 horsepower when pulling loads over a set distance3. Similar performances have been recorded for teams in Europe and elsewhere. Average working performance for one horse is 0.75 to 1.0 horsepower4.
Smil, V. Nature 405, 125 (2000).
Leaflet 225 “Quick Reference Map of Horses and Mules by States” (Horse and Mule Association of America, Chicago, 1936).
Collins, E. V. & Caine, A. B. Testing Draft Horses (Iowa Experiment Station Bulletin 240– Ames, 1926).
Goe, M. R. & McDowell, R. E. Animal Traction: Guidelines for Utilization (Cornell International Agriculture Mimeograph 81, Ithaca, NY, 1980).