Marking transgenic mice by toe clipping of newborns

According to a new ordinance of the Federal Veterinary Office (BVET) issued May 1st, 2010, marking and biopsy taking of mice will have to be combined. Apart from ear punches, a method of choice is the clipping of toe tips of newborn mice. However, the method is discussed controversially from an animal welfare point of view, both by authorities and the public.

In a recent study, we have investigated the short‐ and long‐term impact of toe tip clipping on newborn pups. We have analysed animal welfare aspects, such as health, behaviour, development, stress and detrimental effects in young animals and in adults after toe clipping at postnatal days 3 (P3) and 7 (P7). Our find‐ ings indicate that for both P3 and P7 pups amputations at the second phalange of one toe of each paw do not have any negative effects on growth and physical development and that the clipped pups do not suffer from rejection by their mother. Our data indicate that even though at both ages no abnormalities have been detected in histology, clipping at P7 is the preferable age for an adequate marking mostly because of the small size of the toes at P3. This was also confirmed by grip tests at the age of 12 weeks where P3 animals had lower grip strength than control animals, whereas P7 pups did not show any impairment. Hotplate tests indicated that toe clipping performed at P3 and P7 did not cause hyperalgesia at the amputation stump. Serum corticosterone analysis directly performed on P7 pups after clipping indicated that major stress was pro‐ voked mainly through the handling and not because of the clipping itself. Taken together, these data lead to the conclusion that toe clip‐ ping is from a morphological, physiological and welfare point of view an acceptable method for marking and genotyping newborn mice.

Schaefer D.C., Asner I., Seifert B., Bürki K. and CinelliP. (2010): Analysis of physiological and behavioural parameters in mice after toe clipping as newborns. Lab. Animals 44, 7‐13.