Horse groupings are determined by the amount of prize money the horse has won.
Please note, that racing a horse “up” a level will reset its grouping (but not its prize money).
All horses start off as Group 3. As prize money increases, they will rank up to Group 2. Group 1 is the highest ranking.
Open races can be entered by any horse that is eligible to race in that country, that is, there is no prize money requirement to enter. Any group horse can race in an open race.
Visit the Airport to change between countries. If you have horses entered in races, you will need to wait for them to return before you can change countries.