Which horses are subject to drug testing according to the rules?

The correct response highlights that drug testing is performed on the winning horse and also on selected others. This practice is important to ensure fair competition and the integrity of horse racing. By testing the winner, officials can verify that the horse has not used any prohibited substances that could enhance performance. Additionally, testing selected other horses helps to broaden the scope of checks needed to maintain fairness across the board. The selection of additional horses may be randomized or based on specific criteria, further supporting the regulatory framework designed to uphold the sport's integrity.

This approach helps to deter the use of illegal substances and reassures participants and spectators that all competitors are held to the same rigorous standards. It also allows for the enforcement of rules regarding medication and substances that can impact a horse's performance, ultimately promoting a healthier environment for the sport.