It is important to train your horse before every turn, so that you don’t miss an opportunity to improve its stats for events and perhaps futurefoals.
Therapy Training does nothing at the moment.
Barrels improve speed and agility
Conditioning improves endurence
Dressage improves intelligence, movement, and agility.
Gait Training improves movement
Ground Work improves intelligence
Harness improves strength
Poles improve agility
Sprints improve speed