167 FAECAL STEROID ANALYSES FOR MONITORING REPRODUCTIVE FUNCTION IN POLAR BEARS (URSUS MARITIMUS)

Abstract

Although there has been only limited research on polar bears (Ursus maritimus), it is known that they are seasonal breeders that mate in early spring and experience delayed implantation in the fall, giving birth to cubs in early winter. A non-invasive method for monitoring reproductive function in polar bears would facilitate the management of captive and wild polar bears while expanding the physiological database on this species. Longitudinal faecal steroid analyses were conducted on a captive female polar bear (8 years old) to identify suitable enzyme immunoassay (EIA) techniques for monitoring reproduction. Faecal samples were collected over 23 months (July 2006 to June 2008). In January 2007, the female was introduced to an intact male (17 years old) for breeding. For the first 6 months of the study, faecal samples were collected weekly. However, prior to introducing the male, collection frequency was increased to thrice weekly. Animal keeper staff recorded behaviour daily. Steroid hormones were extracted from 0.1 g of lyophilized faeces by mechanically shaking samples overnight in 3 mL 90% v/v ethanol. Samples were centrifuged at 500g for 10 minutes and the supernatant stored at –20°C until assayed. Immunoreactive progesterone (P₄), estrogen (E₂), progesterone metabolite (PdG) and androgen metabolite concentrations were measured in the faecal samples. Due to the established reproductive seasonality of the species, differences in faecal steroid excretion between breeding (January to June) and non-breeding (July to December) seasons were examined with ANOVA. Values are presented as mean ± SEM dry mass faeces (dmf). Seasonal differences in faecal androgen and PdG excretion were significant (P < 0.05). Baseline androgen metabolite concentrations during the breeding season (124.7 ± 4.8 ng g^–1 dmf) were higher (P < 0.05) than during the non-breeding season (105.6 ± 4.7 ng g^–1 dmf). Peak androgen metabolite concentrations during the breeding season averaged 1108.8 ± 171.2 ng g^–1 dmf and coincided with oestrus behaviour and mating. There was no correlation (P ≥ 0.05) between faecal androgen and E₂ patterns. In addition, there were no increases in faecal E₂ coinciding with mating behaviour or copulation. Therefore, E₂ was deemed unsuitable for oestrous cycle monitoring. Faecal P₄ and PdG results were significantly correlated (P < 0.05). Prior to breeding, PdG concentrations were 167.5 ± 22.5 ng g^–1 dmf. After a March 2007 breeding, the faecal PdG profile appeared to demonstrate a luteal phase (282.5 ± 25.8 ng g^–1 dmf) followed by a PdG spike in mid-October (coinciding with expected implantation) lasting approximately 60 days (1025.5 ± 142.6 ng g^–1 dmf). Concentrations of PdG declined precipitously to baseline in early December, but cubs were never observed with the female in her den. These preliminary data suggest that non-invasive faecal steroid analyses can be used to monitor reproductive function in female polar bears.