The tattoo in the right ear tells the greyhounds age. It consists of the numbers 1 through 12 for the month of birth, followed by the last digit of the year of birth. For example, 103 would indicate the greyhounds was born in October 1993 while 62 would indicate the greyhound was born was born in June 1992. In order to differentiate the greyhounds in the same litter, the letters A, B, C and so on are used. Therefore, greyhounds in the same litter would have the same tattoo in the left ear and in the right ear they would differentiate by a letter of the alphabet. Thus, no one can lie about a greyhounds true age, nor can dogs be "switched" in a race as tattoos are checked prior to the start of each race.
True, the numbers representing years repeat after ten years, but it is generally easy to tell a 12-year old greyhound from a 2-year old.
Other countries have different types of registration systems: Irish greyhounds are also tattooed in their ears, however, the Irish registry uses a series of letters rather than numbers and the tattoos can only be interpreted with the aid of a registry itself.
Pet greyhounds may also be tattooed at their pet owner's request on the inside of the thigh for registration with other organizations such as National Dog Registry (NDR) or Tattoo-A-Pet. Some pet owners have implanted a microchip for further indentification; please consult with your veterinarian concerning this.