This section is from the book "Stable Management And Exercise", by M. Horace Hayes. Also available from Amazon: Stable Management And Exercise.
Gregarionsness (love of association) is largely developed in horses, which consequently as a rule thrive best under conditions of companionship with their fellows. Among semi-wild horses, like those on the Kirgis steppes and Montana ranches, each stallion has his kossiak or "bunch" of brood mares, and the other mares and geldings live in amity-together. I have known a horse in the open, failing association with one of his own kind, seek the companionship of a cow, whose side he would rarely quit. Two horses which work as a pair, or which are close stable companions, as for instance when separated only by a swinging-bail, frequently contract for each other a strong friendship, which one or other will often manifest by loss of appetite and restlessness during his partner's absence. It is evident that in a stable, a stallion should be kept rigidly separated from other horses, and especially from mares. I have pointed out in Illustrated Horse-breaking, that horses recognise mankind far more by the voice than by the appearance, and are quick to perceive differences of meaning conveyed by changes of tone. Hence, a stableman who wishes to be companionable to a horse in his charge, should speak to him as occasion may offer, and should use an invariable tone and an invariable form of words for each respective verbal communication.
 
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