Cal. Food & Agric. Code § 24005

The trainer or owner, or both the trainer and owner, in the absence of substantial evidence to the contrary, is responsible for a horse’s condition and is charged with knowledge of the provisions contained in this chapter and the rules and regulations adopted pursuant to this chapter. If a trainer is prevented from performing his or her duties, including responsibility for the condition of a horse in his or her care, by illness or other cause, or is absent from any event where a horse under his or her care is entered and stabled, the trainer shall immediately notify the secretary or manager of the event, and at the same time a substitute shall be appointed by the trainer. The substitute shall place his or her name on the entry blank at that time. The substitute shall have the same responsibilities as the substituted trainer would have had for the condition of any horse in his or her care.