Led horse

a sumpter horse, or a spare horse, that is led along.
- Swift.

See also: Led

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in classic literature ?
William, without touching the stirrup, vaulted into the saddle of the led horse, and, setting his spurs into its flanks, started off for the Leyden road.
And he caused one of his attendants to mount his own led horse, and give that upon which he had hitherto ridden to the stranger, who was to serve for a guide.
A led horse, one that had been long trained in the hunts, had been brought to receive his master, with but little hope that his services would ever be needed again in this life.
But the most frightened creature I saw, was a led horse that overtook us.