Ano-genital distance as a factor in determining puberty acceleration in mice

The daily exposure of newly born female mice to the urine of lactating mice with a small ano-genital distance accelerated the onset of first oestrus while the urine from donors with a large ano-genital distance was without effect in advancing puberty. The rate of growth of the mice exposed to the urine of lactating mothers was greater than that of a control sample but it was only those mice exposed to the urine of lactating females with a small ano-genital distance which continued to grow, after the cessation of treatment at 21 days of age, at a faster rate. There was no difference in the mass of the uterus when the mice were killed when adult but there were significant age-dependent differences in the mass of the ovaries and adrenal glands. The mice exposed to the urine from lactating mothers (with both large and small ano-genital indices) had smaller ovaries than the control mice while the adrenal glands of mice exposed to the urine of lactating mothers with a large ano-genital index were of greater mass than those of the control mice and mice exposed to mothers with a small ano-genital distance. Exposure to the urine of lactating mothers had no effect on the subsequent activity of the mice when tested in an automated activity recorder. The results confirm that urine from lactating mothers accelerates the onset of puberty and suggests that the effects are restricted to the urine from mothers with a small ano-genital index.