27 Timing of physiological and behavioural oestrous following gonadotrophin treatment in polar bears

There is growing interest in the development of assisted reproductive technologies in polar bears (Ursus maritimus); however, a reliable oestrous stimulation protocol, necessary for performing scheduled artificial insemination (AI) procedures, has not yet been established. Previous oestrous induction attempts (n = 14) by our laboratory included the evaluation of equine chorionic gonadotrophin (ECG), porcine luteinising hormone (pLH), and/or human chorionic gonadotrophin (hCG) in various dosing and timing regimens, most with AIs performed ∼36–48 h following presumed ovulation induction; however, vaginal cytology collected at AI revealed low percentages (14.3 ± 3.5%) of superficial/keratinised cells, suggesting that the hormones, doses, and/or timing of the procedures were suboptimal. To resolve the timing of oestrus relative to hormone administration, an ECG-hCG protocol was implemented in two separate years in a breeding female to determine when she might be receptive to the male. Both years, she was observed breeding six days following hCG, which was later than expected. To establish consistency across individuals, the objective of the current study was to induce oestrus in two females in preparation for an AI procedure scheduled six days following ECG-hCG stimulation. Two 15-year-old multiparous polar bears housed at the same zoological institution were recommended for AI due to lack of an available male. Females were trained to receive intramuscular hormone injections. On 8 March, 25 IU/kg ECG (ProSpec) were administered to promote follicular growth and 72 h later, 55 IU/kg hCG (ProSpec) were given to facilitate follicular maturation and ovulation. Five days following hCG, 43 mcg gonadorelin (Fertagyl^®; Merck) was administered. Bears were anaesthetised either 27 or 30 h later, allowing sampling of vaginal epithelia by passing a cotton-tipped swab through a 15 cm speculum, in duplicate. The swabs were rotated three times, removed, rolled on glass slides, then fixed and stained using Papanicolaou stain. Four separate 100 cell counts were analysed per bear. Cells were scored as parabasal (P), intermediate (I), or superficial (S), and are reported as overall mean percentages (%) ± standard error of the mean. Females began exhibiting behavioural signs of oestrus, such as genital manipulation, 72 h following receipt of hCG. Oestrous behaviours increased in frequency over the next three days and also included vaginal grooming, pelvic thrusting, and mounting each other. Vaginal cytology revealed 0.5 ± 0.3%, 11.4 ± 0.9%, and 88.1 ± 1.1% of P, I, and S cells, respectively, with no differences between females. The high proportion of superficial cells, combined with observed behaviours, suggests that both females were in oestrus nine and six days following ECG and hCG, respectively. Outcome of the AI procedures is pending; however, results support preliminary findings that polar bears may have a delayed response to exogenous hormone treatments intended to stimulate oestrus.