Original Articles

Identification methods in newborn C57BL/6 mice: a developmental and behavioural evaluation

M J Castelhano-Carlos 1, N Sousa 1, F Ohl 2 and V Baumans 2

1 Life and Health Science Research Institute (ICVS), Health Science School, University of Minho, 4710-057 Braga, Portugal; 2 Division of Laboratory Animal Science, Department of Animals, Science and Society, Faculty of Veterinary Medicine, Utrecht University, 3584 CM Utrecht, The Netherlands

Corresponding author: M J Castelhano-Carlos. Email: [email protected]

The use of group-housed rodents in many fields of biomedicalresearch imposes a need to identify individuals in a cage. Fewstudies have been designed to assess possible negative effectsof identification methods of newborn mice on their developmentand wellbeing. In the present study, three different identificationmethods were applied to newborn C57BL/6J mice on postnatal day(pnd) 5 (toe clipping, toe tattoo ink puncture and subcutaneousimplantation of a small transponder). All identification methodsused proved to be effective for long-term marking of individualanimals. Newborn mice showed the least reaction to toe clippingfollowed by toe tattoo ink puncture and transponder implantationwas the most distressful individual identification procedurein newborn mice. Importantly, clipped toe tissue proved to beenough for genotyping purposes. No overall consistent differencesin somatic and neurological reflex development during the postnatalperiod were shown as a result of the newborn individual identificationprocedures used. Further, none of the methods interfered significantlywith the adult animals’ general normal behaviour (e.g. abilityto move, grasp, climb) and sensory–motor functions asassessed with a simplified SHIRPA battery of tests, as wellas Rotarod and Elevated Plus Maze tests. Postmortem thymus andadrenal gland weights gave no indication of chronic stress asa consequence of the identification method. We conclude thattoe clipping might even be advisable in newborn mice at a veryyoung age, when genotyping is needed. Toe tattoo ink punctureis also a good identification method for newborn mice and transponderimplantation should only be used in older newborns or appliedat weaning.