All American Quarter Horses that are racing must be tattooed prior to entering their race by an AQHA representative to be eligible to compete.
American Quarter Horses that compete on the racetrack are required to be tattooed prior to entering a race by an AQHA representative. Tattoos are an additional means of identification of a racehorse. They are used along with the horse's markings, color, age and sex. The horse identifier at the racetrack verifies that each horse entered in a race matches this information as recorded on its official AQHA registration certificate.
Before you are able to get a tattoo and enter a race, the American Quarter Horse must be geno-typed and parentage verified. This can be completed when registering a foal. If your horse has not been genotyped or parentage verified, you can order those kits here.
Once your horse has met these requirements, you can contact a tattooer. Many of the tattooers provide the racetracks with a schedule of when and where they will be tattooing. A list of tattooers and their contact information is available here. Some of the tattooers will make appointments to meet the customer at a farm or ranch, if there are enough horses available to be tattooed. Tattooers set their own schedules and are not required to be available daily.
The tattooer will then record the tattoo number, the tattoo date and the tattoer’s name on the horse's registration certificate. On AQHA's new registration certificates, the tattoo information will be recorded on the back. Tattoo numbers are also recorded in AQHA's database as a part of each horse's permanent record. Should a horse be lost or stolen, it can be identified via the tattoo and the last recorded owner can be notified by cross-references in the AQHA database.
Read here for more information on tattooing.