
I've been thinking on how we could propose this as a worthwhile addition to the game.
In terms of usefulness...
Horses can be rode from place to place; perhaps at run speed without loss of stamina. Similar to dragging a cart over paved road.
Horses can be harnessed to drag logs or pull a cart, though they cannot pull as much weight as oxen.
In some places IRL; female horses are milked and the milk is fermented into a mildly alcoholic drink.

Horses are nice to look at! With a large range of colors other than boring brown.
In exchange for the speed at which the horse would pull/run/work at,
taming a horse could be more difficult than taming other animals, or perhaps bands of horses could be very rare.
Skills that would be required to tame a horse could be "Horsemanship", and later, "Horseback Riding".
Or combine the two and make it less of a challenge...

As for the sprite...I think a Przewalski's-esque horse would fit in nicely with the heath/moor environment.
See photo: http://www.britannica.com/blogs/wp-content/uploads/2011/05/Przewalski.jpg
The way I was thinking of it is that you make the horse quite beneficial,
but hard to find, catch and tricky to keep in perfect condition...as horses are.

Feel free to add to this!