Emerald Downs and the racing commission have no control over how trainers work their horses. Horses are sometimes given illegal painkillers and stimulants to improve performance and mask injuries. Illegal opiates are universally condemned. It also tests four horses at random and three others selected on race day because of unusual positive or negative performances. Thorough examinations by independent vets before and after races may be the most critical aspect of preventing catastrophic injuries.
Vets also watch the horses as they warm up and enter the paddock.
Finally, horses are inspected after a race, and film of every race is reviewed. Injuries sustained or abnormalities created during this period often become problems as the horse ages. You hear it every once and a while. It's a personal decision made by owners and trainers.