Infantile development and sexual maturation. Infantile development and sexual maturation according to weaning age in male (A, C) and female rats (B, D). (A, B) Developmental milestone for infantile (pre-weaned) rats were observed daily from d7 to 20: fur budding (d9 milestone), incisor eruption (d10), pinnae detachment (d12) and eye opening (d16). (C) Testicular size was determine daily as of d30 using a self-built orchidometer based on the human Prader orchidometer with mock-ups ranging from 0.5 to 5 ml. Gonadarche was defined when testicular volume reached 1 ml. (D) The initial day of vaginal opening (solid bars) was determined as of d30. First estrous (open bars heavy frames) were determined as of d36 by observing vaginal smears for more than 50% cornified epithelial cells. Statistically significant differences between d16 and d26 rats are indicated by (&) for P <0.05, (*) for P <0.001 with a two-way t-test. Dotted line shows enhancement of the traits from F1 to F3; (@) for P <0.01. Mean ± SEM, n = 8 to 12 per group.