By Lillian Bacheller and George Wiggans
Before the adoption of the American ID, a new ID entering the system with the same pedigree as an existing ID was usually identified as the same animal if one ID was an eartag and the other a registration number. Although the American ID system was expected to eliminate the possibility of animals getting multiple ID's, in practice this still occurs, and the previous method of comparing eartag and registration numbers is unavailable. Animals may also receive additional ID's from other countries. A system for considering ID's for possible cross referencing was developed that is applicable to the American ID system, and previous identification systems. When animals are found to have siblings with the same or close birth dates, one ID may be deleted as invalid, ID's may be cross referenced, or multiple birth codes may be assigned. Multiple birth and ET codes found in one or more records under comparison prevent the combining of data. An ID is considered invalid if it is similar to an existing ID with a digit switch or a shift of digits.