Retiring horses!
(Not really that exciting, I suppose, but a big feature for the game as a whole - trying to replicate the functionality of the current site so that we can switch over and then add all the awesomeness.)
You should be able to retire:
- racehorses, if they’re not entered to race
- broodmares, if they’re not currently in foal
- stallions (anytime)
You should not be able to retire:
- Babies
- Retired horses
- Dead horses
The “Retire” button will appear under “Options” on the right side of your horse’s page. It will list all the options for retirement (e.g. for racing colts, Retired & Stallion), and either a checkmark or an X depending on whether it’s a valid option (non-studified colts will have an X next to Stallion). Once you select an option and click Retire, you’re done. 
Feel free to play around with it - the data import that runs overnight will un-retire any horses (based on their current status in the game), so no worries about doing anything permanent.
Plus, unless it killed the foal, it’s not very realistic as the mare doesn’t “retire” from being pregnant until she foals.)