The section on Identification and Records (Guide for the Care and Use of Laboratory Animals (Guide) NRC 1996) indicates the following means of animal identification: “...room, rack, pen, stall, and cage cards with written or bar-coded information; collars, bands, plates, and tabs; colored stains; ear notches and tags; tattoos; subcutaneous transponders; and freeze brands. Toe-clipping (removal of the first bone of certain toes, corresponding to a predetermined numbering code1), as a method of identification of small rodents, should be used only when no other individual identification method is feasible and should be performed only on altricial neonates.”

Under certain circumstances the techniques of “toe clipping” for the purpose of animal identification may be necessary. However, the NIH Interagency Research Animal Committee considers the “toe clipping” method of marking an animal as a potentially painful procedure which should be discouraged and only done with the approval of the Institutional Animal Care and Use Committee (IACUC). The principal investigator must justify to the IACUC that no other methods of marking the animal is feasible. The IACUC must also be satisfied that the procedure will be performed in the most painless and humane way and that it will consider all accepted veterinary procedures, including anesthesia and antisepsis. The evaluation and approval criteria are set forth in the U.S. Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research and Training, and the Guide.

Reference
1. ALAT Manual, American Association for Laboratory Animal Science, 1998: page 57