From publisher blurb:
Need a horse? Why not pick up a quirky gelding or an energetic filly? You can find both of those and much more in Horse Trader. From loyal stallions to donkeys that know how to count, if you can put a saddle on it, you can benefit from a visit to the Horse Trader.
Contains basic information about horses, some vocabulary to help players and GM talk about horses, a system for adding personality quirks to horses, and lastly rules for teaching horses new abilities beyond acting as a mount.