The European mink (Mustela lutreola), one of Europe's most endangered mammals, has become extinct throughout most of its former range. Population decline of this semi-aquatic carnivore has mainly been caused by habitat destruction and invasion of American mink (Neovison vison). A European Endangered Species Program (EEP) for captive breeding and reintroduction is coordinated by the Species Conservation Research Lab at Tallinn Zoo, Estonia. This study has been designed to augment our knowledge about the reproductive physiology of the female European mink, i.e. estrus, ovulation and pregnancy, in order to support practical breeding management. Fecal reproductive hormone metabolites were analyzed with enzyme immunoassays for 20-oxo-pregnanes and estrogens.
For estrus detection, percentage of cornified cells in vaginal lavages was correlated with estrogen and pregnane metabolite levels in 11 females. The European mink is regarded as seasonally polyestrous. This was confirmed by estrogen fluctuations and cornified cell levels showing several peaks in most females. Both estrogen and 20-oxo-pregnane levels were significantly elevated in pregnant females as compared to non-pregnant females. For reliable pregnancy diagnosis the large individual variability requires more than one sample point. Increasing 20-oxo-pregnane levels after hCG (human chorionic gonadotropin) treatment closely resembled the profile of pregnant females and thus support the assumption that ovulation in the European mink can be induced by hCG. Fecal hormone metabolite analysis can be of use as a non-invasive method to support population management of this highly vulnerable species.