Horses of Hoofprint Bay: How Do I Separate Stallions?
Short answer
Suggested fix (unconfirmed): Upgrade your stable so you have two or more groups of horses. Then, switch the horses between groups using the "manage" option for each horse.
No confirmed fix yet. Players suggest: if you have too many problems in the second competition you can enable auto-jump, but beware that your pace still has to be right!
Suggested fix (unconfirmed): Separate mares and stallions into different stable groups by using the "Manage" button or by clicking and dragging the horses. Alternatively, geld your stallions.