9 C.F.R. § 11.5
Any horse owner, trainer, exhibitor, custodian (or any other person responsible for entering the horse in an event), or transporter may appeal to the Administrator on whether a disqualification decision concerning a horse at a horse show, horse exhibition, horse sale, horse auction, or other covered event was justified. The APHIS representative or HPI will provide the inspection report to the custodian following the disqualification. There may only be one appeal per disqualified horse per event; however, all parties with interest in the disqualification may contribute to the appeal. To appeal, the horse owner, trainer, exhibitor, custodian (or any other person responsible for entering the horse in an event), or transporter must send a written statement contesting the disqualification and include any documentation or other information in support of the appeal. To receive consideration, the appeal must be received by the Administrator, preferably by electronic mail, to horseprotection@usda.gov within 21 days of the date the horse owner, trainer, exhibitor, custodian (or any other person responsible for entering the horse in an event), or transporter received the disqualification that is the subject of the appeal. If expedited review of the appeal is requested, this must be noted as such, and information in support of this request must accompany the appeal. The Administrator will send a final decision, in writing via either electronic mail or postal mail, to the person requesting the appeal as promptly as practicable.
9 C.F.R. §11.5
Appeals may also be sent by U.S. mail to APHIS, 2150 Centre Ave, Bldg. B, MS 3W-11, Fort Collins, CO 80547.