Identification of newborn rats by tattooing

Pups were identified by toe clipping or tattooing the plantar surface of the paws on day 4 after delivery. Their growth, maturation, and reproductive capability were not affected by either identification method. In the toe clipping group, however, the duration until fall in the suspension test was significantly shortened, indicating that this identification method may not be suitable for some behavioural tests. The clipping also disturbs the skeletal investigation of toes and is not recommended from the view point of animal welfare. Palm tattooing, on the other hand, satisfies the fundamental requirements for long-term identification of rats.