Cytologic Assessment of the Vaginal Epithelium in the Common Marmoset (Callithrix jacchus): A Preliminary New Approach to Reproductive Screening

The application of vaginal cytology in defining reproductive events is a widely accepted and applied diagnostic tool in many species. Here we present a preliminary approach to recognizing a correlation between changes in vaginal epithelial cytology and circulating plasma progesterone in the common marmoset, Callithrix jacchus, such that vaginal cytology could be diagnostically appropriate for reproductive management. We assessed six captive-born adult female common marmosets for the duration of one complete estrus cycle. Cytologic samples, collected by vaginal swab, and blood for plasma progesterone concentration were collected twice weekly. Cytologic samples were blindly assessed, and vaginal epithelial maturation was defined on the basis of the karyopyknotic index (KPI). In the three consistently cycling females (cj0328, cj0732, and cj0678), a marked increase in KPI corresponded with rising plasma progesterone levels, which subsequently decreased throughout the duration of follicular phase. The remaining three females who had previously irregular estrus cycles (cj0608, cj0680, cj0724) demonstrated irregularity in their progesterone profiles which correlated with inconsistent KPIs. Although KPI is not a very sensitive single sampling indicator of ovulation, evaluating changes in cytologic morphology over time aid in predicting the timing of an ovulatory event. Our results suggest that vaginal cytology can be an effective alternative to blood sampling for reproductive management of the common marmoset.