Etain comes to mind.. as i recall she is daughter to Rhiannon, who's earthy form is represented by the horse.

Rhiannon, is the protector of the O'Connor's, and i am of that house.

Rhiannon was a very powerful god, and to this day, celts, and even most anglo saxons, refrain from eating horse meat.

Rhiannon, of course was a mare, not a stallion-- all of the most powerful god were female, and gave birth.. giving birth is the most god like thing humans can do. it is a powerful act of creations, and it is entrusted to woman.