Xenophon On the Art of Horsemanship 5

[1]
  It is a mark of a good horseman, in our opinion, to see that his groom, like himself, is instructed in the way in which he should treat the horse.

  First then the man ought to know that he should never make the knot in the halter at the point where the headstall is put on. For if the halter is not easy about the ears, the horse will often rub his head against the manger and may often get sores in consequence. Now if there are sore places thereabouts the horse is bound to be restive both when he is bridled and when he is rubbed down.

[2] It is well also for the groom to have orders to remove the dung and litter daily to one and the same place. For by doing this he will get rid of it most easily and at the same time relieve the horse.

[3] The groom must also know about putting the muzzle on the horse when he takes him out to be groomed or to the rolling-place. In fact he must always put the muzzle on when he leads him anywhere without a bridle. ¹ For the muzzle prevents him from biting without hampering his breathing; and moreover, when it is put on, it goes far towards preventing any propensity to mischief.

[4]
  He should tie up the horse at a place above the head, because when anything irritates his face, the horse instinctively tries to get rid of it by tossing his head upwards; and if he is tied thus he loosens the halter instead of breaking it by tossing up his head.

[5]
  In rubbing the horse down, the man should start at the head and mane; for if the upper parts are not clean, it is idle to clean his lower parts. Next, going over the rest of his body, he should make the hair stand up with all the dressing instruments, ² and get the dust out by rubbing him the way the hair lies. But he should not touch the hair on the backbone with any instrument; he should rub and smooth it down with the hands the way it naturally grows; for so he will be least likely to injure the rider’s seat.

[6] He must wash the head well with water, for, as it is bony, to clean it with iron or wood would hurt the horse. He must also wet the forelock, for this tuft of hair, even if pretty long, does not obstruct his sight, but drives from his eyes anything that worries them; and we must presume that the gods have given the horse this hair in lieu of the long ears that they have given to asses and mules as a protection to their eyes.

[7] He should also wash the tail and mane, for growth of the tail is to be encouraged in order that the horse may be able to reach as far as possible and drive away anything that worries him, and growth of the mane in order to give the rider as good a hold as possible.

[8] Besides, the mane, forelock and tail have been given to the horse by the gods as an ornament. A proof of this is that brood mares herding together, so long as they have fine manes, ³ are reluctant to be covered by asses; for which reason all breeders of mules cut off the manes of the mares for covering.

[9]
  Washing down of the legs we disapprove of; it does no good, and the hoofs are injured by being wetted every day. Excessive cleaning under the belly also should be diminished; for this worries the horse very much, and the cleaner these parts are, the more they collect under the belly things offensive to it; ⁴

[10] and notwithstanding all the pains that may be taken with these parts, the horse is no sooner led out than he looks much the same as an unwashed animal. So these operations should be omitted; and as for the rubbing of the legs, it is enough to do it with the bare hands.