Semen cryopreservation in Bornean Sun Bear (Helarctos malayanus euryspilus)

Semen cryopreservation is one common tool for extended genome storage and serves as insurance for declining biodiversity. In the endangered Bornean sun bear, semen was collected with electroejaculation and this is the first attempt at semen cryopreservation for this subspecies. Chilled semen with motility of more than 50 % was extended with Caniplus freezing medium, and cryopreserved with slow freezing protocol. A total of 22 cryopreserved semen straws were evaluated with computer-assisted sperm analysis and conventional semen evaluation tests as well as additional functional tests including evaluation of the acrosome (Rose Bengal Fast Green stain), plasma membrane (hypoosmotic swelling test), and chromatin (toluidine blue stain). Post-thaw semen quality was compromised with poor viability (27.6 ± 11.2 %), motility (8.3 ± 7.1 %), and progressive movement (1.3 ± 2.0 %) but maintained high integrity for the acrosome (71.1 ± 10.8 %), plasma membrane (54.7 ± 9.6 %), and chromatin (89.7 ± 7.6 %). The total post-thaw sperm abnormality was 51.7 ± 10.7 %, predominantly bent tail (28.0 ± 7.6 %) and proximal droplets (20.0 ± 11.8 %). Although this current cryopreservation was not a success, the compromised frozen-thawed semen may be a valuable resource in assisted reproductive technologies such as intracytoplasmic sperm injection. The three additional functional tests demonstrated were simple and affordable and hence are recommended to be part of the routine semen evaluation. Further research is required to develop species-specific cryopreservation protocols and to explore other assisted reproductive technologies in the Bornean sun bear.