... In each generation, the litters were reduced to 8, 4 males and 4 females, on day 4 post-partum. Observations in F1b and F2b pups included pinna unfolding, hair growth, incisor eruption and eye opening, righting reflex, pain reflex,...
http://www.inchem.org/documents/jmpr/jmpmono/v91pr05.htm