originally meant horses bred in the midland and eastern shires of England, but now mean any draught-horses of a certain character which can show a registered pedigree. The sie and dam, with a minute description of the horse itself, its age, marks, and so on, must be shown in order to prove the claim of a “shire horse.” Shire horses are noted for their great size, muscular power, and beauty of form; stallions to serve cart mares.
Clydesdale horses are Scotch draught-horses, not equal to shire horses in size, but of great endurance. A hackney is not a thoroughbred, but nearly so, and makes the best roadster, hunter, and carriage-horse. Its action is showy, and its pace good. A first-class roadster will trot a mile in two and a half minutes. American trotters sometimes exceed this record. The best hackneys are produced from thorough sires mated with half-bred mares.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894