Pinna Edge Biopsy of 7 and 21 Day Old C57BL/6 Mice as a Method for Identification and Genotyping

Identifying and genotyping mice prior to weaning can be useful for mouse colony management. Mice of an undesired genotype can be identified prior to weaning and removed from further study, resulting in a reduction of housing costs, and labor time. We hypothesized that a pinna edge biopsy (PEB) performed by removing a portion of its edge with scissors is a reliable method for identifying and genotyping mice on postnatal day (PND) 7 consistent with PND 21, weaned mice. The pinnae of 54 C57BL/NCrl6 mice were biopsied on PND 7, and another 54 were biopsied on PND 21. Nine pinna patterns were tested. The accuracy of pattern identification was assessed on PND 7, 14, 21, 30, and 63. The mean times were compared for performing the biopsy on PND 7 and PND 21 mice, and the average time taken to identify the patterns were determined. Weight, milk spot presence, pup rejection, morbidity, and mortality were examined at various time points. During the biopsy, bleeding of the pinna, urination, vocalization, and flinching were assessed. No significant differences were detected in DNA quality, relative DNA quantity, genotyping reliability, or body weight (P ≥ 0.05) between mice biopsied on PND 7 and PND 21. Flinching at the time of PEB was significantly higher in PND 21 mice as compared with PND 7 mice (P < 0.00001). Pinna pattern identification accuracy for mice biopsied on PND 7 and PND 21 were 96% and 98%, respectively. This study validates the use of PEB for simultaneous identification and genotyping of PND 7 mice.