Characterization of the Estrous Cycle in Bears

Of the eight species of bear, six are classified as endangered or threatened. Given the intensive efforts of conservation researchers, more is currently known about the basic reproductive biology of the most rare and critically endangered bear species, the giant panda, than is known about any other ursid. Detailed knowledge of the daily dynamics of the estrous cycle are essential to improve captive husbandry (predict estrus and timing of birth), to assess fertility and health (monitor gonadal function, detect endocrine abnormalities), and to successfully use assisted reproductive technologies (timing of artificial insemination, etc.).

The primary goal of the current research proposal is to characterize the estrous cycle of all bear species (completed for giant panda and in process for sun bear, American black bear and polar bear) by simultaneously examining physiology, morphology, endocrinology, and behavior data and correlating these parameters to each other. Non-invasive methods were used to collect the endocrine samples (urine, feces), and operant conditioning (training) was used to collect vaginal cell samples. Non-radioactive assays for urinary and fecal estrogen and androgen hormones and their metabolites were validated and adapted for use under semi-field conditions.

By combining multiple measures of reproductive activity, a more accurate picture of the estrous profile is obtained, and events such as ovulation can be predicted with greater accuracy. Each measure provides a means of validating and cross-checking the other. These data can be used for in situ conservation by providing important reference profiles by which to evaluate the reproductive health of individuals and the species overall and their response to environmental degradation (pollutants, stress, etc.).