Lasix

[Riot]

A vet has to observe and certify that the horse bled in a work or a race, and the horse can then go on the offical "bleeder's list" so it can get the drugs to try and prevent bleeding.

Horses that have bled are tracked by the offical track vet, and have varying periods of mandatory time off from racing after a bleeding episode.

The various jurisdictions have their own regulations.