26 Evaluation of polar bear (Ursus maritimus) sperm collection and cryopreservation techniques

Polar bears (Ursus maritimus) are classified as threatened with extinction because of diminishing sea ice and associated physiological consequences, including starvation, drowning, cannibalism, and reduced reproductive efficiency. Efficient sperm collection and cryopreservation methods could facilitate the assessment of the impact of climate change and other anthropogenic factors on male fertility and allow for preservation of genetic material. Over the last decade, 35 opportunistic procedures were conducted to collect semen from 15 polar bears managed in North American zoological institutions (1–5 procedures/bear). Samples were collected via electroejaculation (EEJ; n = 6) and/or urethral catheterisation (UC; n = 25), and sperm were rescued from the testes of deceased males (n = 4). Collections occurred both during breeding season (winter-spring; Jan 1 to May 21) and nonbreeding season (spring-winter; May 22 to Dec 31). Because of limited sample size, statistical analyses beyond descriptive statistics were not warranted. EEJ resulted in sample acquisition only once (17%) and the sample was of minimal volume (<100 µL; motility: 50%); five of the six EEJ procedures occurred during breeding season. UC resulted in successful sample acquisition in 16 (64%) collections (395.9 ± 171.8 µL; motility: 62.8 ± 7.8%). Of the nine unsuccessful collections, three were conducted during the nonbreeding season, four occurred very early in the breeding season, one male was immature, and one sample contained only urine. Of the successful collections, only one was conducted outside of the breeding season. Sperm was successfully rescued from testicular or epididymal tissue (motility 55.0 ± 15.0%) and cryopreserved from two males (50%). The other two males were found to be aspermic. Multiple semen extenders including an egg-yolk based equine extender (EQ + 4% glycerol; n = 7), TEST egg-yolk buffer (TEY + 4% glycerol; n = 2), coconut product-based extenders (COCO; n = 1; Wojtusik et al. 2018 Theriogenology 121, 72-77), and animal protein-free OptiXcell (OP; n = 1; IMV Technologies) were tested for use in cryopreservation. In both EQ and TEY, post-thaw motility was low (27.1 ± 6.3%). The use of COCO extenders resulted in complete viability loss pre-freeze. Preliminary data suggest OP is a comparable alternative (n = 1; motility: 30–40%) to egg yolk-based extenders for polar bear semen, and further evaluation is planned. In conclusion, UC is more likely to result in successful sperm collection, especially if performed later during the breeding season (March to May); however, further efforts to optimise sperm cryopreservation procedures are warranted.

This project was made possible in part by the Institute of Museum and Library Services grant #MA-30-18-0461-18.