Fantastic Crests of the Middle Ages :

The Horse

 

What is more natural than to see the horse honored by the knight.

But this symbolism comes from Celtic myth, where the horse is the God of the ground.  Where as in the Greco-Roman mythology the horse was in the form of a half man, half horse Centaur and as Pegasus the winged horse.

In pagan cultures, the horse is a symbol of youth, force, speed and masculine sexuality. But in the Old Testament, the horse is a symbol of foreign domination and decadent luxury. In the New Testament the horse became the symbol of obedience and docility, and victory.

Gilbert Motier de La Fayette chose for his crest a horse's head wearing the proper harness, wreath Argent, Azure and Or, mantled Gules doubled Azure (coat-of-arms:Gules, a bend Or within a bordure Vair).