No veterinarian shall permit a horse in his care to be started if he knows or if by the exercise of reasonable care he might have known or have cause to believe, that the horse has received a drug, stimulant, sedative, depressant, medicine or other substance that could result in a positive test.
58 Pa. Code § 183.356
This section cited in 58 Pa. Code § 183.361 (relating to winnings when rule is violated).