Age- and hormone-related changes in vaginal smear patterns in the gray-tailed vole, Microtus canicaudus

Female voles, Microtus canicaudus, exhibited age-related changes in vaginal smear patterns when isolated from males after weaning. Between 30 and 50 days of age, nearly all females exhibited persistently leucocytic vaginal smears. By 90-120 days, most females showed vaginal cyclicity with alternating predominance of leucocytes, nucleated epithelial cells or cornified epithelial cells. Most females examined between 150 and 200 days of age exhibited persistent vaginal cornification. The vaginal cyclicity seen in females between 90 and 120 days was not a reflection of cyclic ovulatory changes; plasma progesterone concentrations remained constant, regardless of age or vaginal smear pattern, and corpora lutea were never seen in unmated females. Although progesterone concentrations did not differ among vaginal smear patterns of 120-day-old females, plasma oestrogen values were highest in females exhibiting vaginal cornification.