Horse-holder is a term that seems to have so far fallen out of usage that I can’t find it in my NSOED. With the passing of dragoons and dismounted cavalry, there’s not much, if any, call for them. Maybe they were never very popular; vide Kipling:
“The new fat regiments come from home, imaginin vain V.C.’s
(The same as our talky-fighty men which are often Number Threes)”
Despite Kipling’s indictment of “talky-fighty men,” who exist at all times and in all arms and branches, the role of the horse-holder was of vital importance, first in the dragoons, who from their first apparition dismounted to fight on foot, and later among the cavalry of the 19th c., beginning with the American Civil War, who fought with equal skill mounted and dismounted. Mainly, they kept the mounts of the men on the firing line in hand, out of harm’s way, and ready to meet any offensive or defensive circumstances that eventuated.
Dur Écu did a quick, imperfect survey of the proportion of horse-holders to shooters and found:
1 in 10 were horse-holders in the Thirty Years’ War and in Marlborough’s day
1 in 4 in the American Civil War and afterward
1 in 3 on the continent of Europe (France, Germany, Russia, etc.) post-1866
1 in 3 in Britain to 1883 (Kipling’s Number Threes)
1 in 4 in Britain 1883-1914
The proportions shown seem to have reflected the relative proportion of shooters needed to put up a credible defense (by fire combat) with weapons and doctrine in use at different periods. I say seem, because I think this needs to be investigated further.