The phrase is American first appearing in print in 1844.
“Oh, hold your hosses, Squire. There’s no use getting’ riled, no how.” – The Picayune (New Orleans) newspaper September 1844.
A century late, the phrase got a second wind in the rural south after WWII. Steam engine tractors were becoming an affordable option to plowing by mule. Steam engines had one big draw back, they were loud. The operator communicated to the field crew by blowing a steam whistle. The whistle spooked the horses so bells were mandated. If a tractor operator drove up behind a team of horses or mules, he would ring the bell and as courtesy call out to the wagon driver “Hold your horses.”