The Bretonnian Warhorse are the finest breed of Warhorse in the Old World. This is because the Bretonnian Warhorse is in part, are the descendants of the Elven steeds of the former Elven colonies which flourished centuries ago in the land that is now Bretonnia. When the Elven colonists abandoned the Old World and sailed back to Ulthuan, some remained behind. These Elves were the ancestors of the Wood Elves of the Athel Loren. One of the Elven kindreds that stayed took their Elven steeds with them into the safety of the forest glades. Elsewhere, herds of Elven steeds roamed freely in the meadows and plains around the abandoned Elven ruins, interbreeding with wild forest ponies. This mingling of blood eventually resulted in the creation of a new breed of horse known simply as the Bretonnian Warhorse.
This new breed of horse was far superior in size and spirit than any other in the Old World. The horses of the Empire are descended from the wild ponies of the Kislevite steppes and have no blood of the Elven steeds in their veins. The warhorses of the Empire and Kislev are passable, but lack the power and spirit of the Bretonnian steed, although they are perhaps better suited to a harsher climate, while the Bretonnian breed requires the lush meadows of Bretonnia's landscape. When the Bretonnian warriors began riding into battle on the native horses of Bretonnia, they found that the horses could bear the weight of a fully armored man and still gallop and charge over and over again without tiring. The horses were big, powerful and not lacking in stamina. The Bretonnian Knights therefore made every effort to maintain and improve their special breed. A very important factor in this was the peace pact with the Wood Elves of Athel Loren. By the terms of this pact, from time to time the Elves allow the Bretonnians to have some of their precious steeds. In this way the Bretonnian horses are replenished with fresh blood from pure Elven stock. Bretonnian knights owe their success not only to their own valor and skill, but also to the endurance and temper of their steeds.
Naturally, only a noble is permitted to ride a warhorse, though a few lucky and trusted peasants may be allowed to act as grooms and stablehands, and thus sleep in the same barn as one. Squires must make do with forest ponies and lesser breeds lacking the blood of the Elven Steeds. So highly valued are these beasts that a Royal Decree of many centuries standing forbid the export of these magnificent animals. The Bretonnian Knights naturally do not want anyone else to be as well mounted as they are. Even so, you would have to have the stature and nobility of a true Bretonnian Knight to ride a Bretonnian Warhorse. They do not put up with lesser warriors on their backs.
- Warhammer Armies: Bretonnia (7th Edition) -- pg. 57