Noninvasive monitoring of female reproductive hormone metabolites in the endangered European mink (Mustela lutreola).

This study examined the reproductive physiology of female European mink (Mustela lutreola) to augment the available information on estrus, ovulation, and pregnancy with the long-term goal of supporting ex situ breeding management of this highly endangered species. Fecal reproductive hormone metabolites were measured using EIAs for estrogen and 20-oxo-pregnane metabolites. Seasonal hormone profiles were established. A comparison of hormone fluctuations in pregnant and nonpregnant females showed that both estrogen and 20-oxo-pregnane metabolites were significantly elevated during gestation, which is 42 days in length. Delayed implantation or embryonic diapause does not occur in this species. Litter size was correlated with 20-oxo-pregnane levels but not with estrogen concentrations. During lactation, 20-oxo-pregnane metabolite levels remained higher than in nonpregnant females. The breeding season was characterized by peaks in vaginal cornified cells and fecal estrogen metabolite levels. Up to four peaks in estrogen levels were identified and confirmed that European mink are seasonally polyestrous. The results of 20-oxo-pregnane measurements indicated that hCG can be applied to induce ovulation. With the establishment of this noninvasive method, we present a new tool to support population management of this species.

The causes of the low breeding success of European mink (Mustela lutreola) in captivity.

High among-individual variation in mating success often causes problems in conservation breeding programs. This is also the case for critically endangered European mink and may jeopardize the long-term maintenance of the species' genetic diversity under the European mink EEP Program. In this study, breeding success of wild and captive born European minks at Tallinn Zoological Garden are compared, and the mating behavior of the males is analyzed. Results show that wild born males successfully mate significantly more often than captive born males (89% and 35%, respectively). On the basis of an extensive record of mating attempts, both male aggressiveness and passivity are identified as primary causes of the observed mating failures. All other potential determinants have only a minor role. Mating success as well as a male's aggressiveness and passivity are shown to depend more strongly on the male than the female partner. We did not find any evidence that the behavior of an individual is dependent on the identity of its partner. We suggest that aggressiveness and passivity are two expressions of abnormal behavior brought about by growing up in captivity: the same individuals are likely to display both aggressive and passive behavior. The results point to the need to study and modify maintenance conditions and management procedures of mink to reduce the negative impact of the captive environment on the long-term goals of the program.