26 Isothermal collection of bison semen in wild conditions

North American bison suffered a near-extinction event at the turn of the 20th century and, at less than 2% of historic numbers, remain a threatened species. To facilitate species recovery, we have established a bison germplasm biobank. The objective of the study was to develop an isothermal semen collection method that may be used in field settings to mitigate the effects of temperature fluctuations on sperm. Initial development involved testing under controlled laboratory conditions. A 15-mL conical collection tube was inserted through the cut nipple of a 150-mL baby bottle filled with 130 mL of water. The elastic tension of the cut end of the nipple provided sufficient friction to hold the bottle and semen tube as one. Using 5 mL of semen extender in the collection tube, a 2 × 3 factorial experiment was done to compare heat loss from the collection tube with vs without the insulating apparatus at ambient temperatures of 23°C, 4°C, or −10°C. For each ambient temperature, 3 replicates were done, each consisting of 2 insulated samples and 1 uninsulated (control) sample (i.e. n = 6 in the insulated group and n = 3 in the control group at each temperature). Samples were prewarmed to 32°C, and temperature changes were recorded over an exposure period of 20 min using a thermocouple logger. Data were analysed by ANOVA. Compared to uninsulated controls, the rate of cooling was lower and the final temperature after 20 min was higher in the insulated group, but both endpoints were strongly influenced by ambient temperature (apparatus-by-ambient temperature interaction, P < 0.0001). Compared to uninsulated controls at 23°C, 4°C, and −10°C, respectively, the rate of cooling over 20 min was decreased by 63%, 54%, and 54% using the isothermal apparatus. Sample temperature at the end of the test period at ambient temperatures of 23°C, 4°C, and −10°C, respectively, was 29.4 ± 0.1°C, 20.5 ± 0.3°C, and 18.1 ± 0.5°C in the isothermal device group and 25.1 ± 0.1°C, 6.8 ± 0.4°C, and 1.3 ± 1.9°C in the uninsulated control group. Sample temperature was maintained at ≥20°C for a longer period with the isothermal device than in the uninsulated control at an ambient temperature of 4°C (19.8 ± 0.2 min vs 5.0 ± 0.0 min) and −10°C (17.4 ± 0.7 vs 5.0 ± 0.5 min; interaction P < 0.001). Field testing was carried out on free-roaming bison at Elk Island National Park in Alberta Canada. Ten bison bulls were located and dart-immobilized over a period of 5 days in July (ambient temperature 14°C to 26°C), and semen collection was attempted by electroejaculation. Satisfactory ejaculates (>1 billion sperm with >75% total motility) were collected from 5 bulls, and a total of 284 straws (1/2 mL) of semen were cryopreserved. In conclusion, the isothermal semen collection system was effective at slowing the cooling of the sample at all ambient temperatures tested and maintained a temperature of ≥20°C for ≥17 min at ambient temperatures above −10°C. The apparatus is simple, practical, and enabled cryopreservation of bison semen collected in a wild setting.

This research was supported by funding from the Saskatchewan Agriculture Development Fund, Genome Canada, and the WCVM Summer Student Research program.