Vaginal opening in the Mongolian gerbil, Meriones unguiculatus: normal data and the influence of social factors.

Mean age at vaginal opening was 41 days, range 33-53 days. Bodyweight at weaning and age at vaginal opening were negatively correlated, but there was no relationship between bodyweight and age at vaginal opening. The presence of a male before vaginal opening did not accelerate either the time of its occurrence or first conception. The vaginas of females caged singly from weaning opened earlier than in those kept in groups of 2 or 3.