Change of physiological and morphological sperm quality traits in reindeer (Rangifer tarandus) during cryopreservation

Assisted reproductive technologies allow effective preservation and use of endangered animal gene pool and creation of new breeding forms. In reindeer ( Rangifer tarandus ) herding, the technique of sperm cryopreservation is still under development. This is due to the difficulty of collecting reindeer sperm in the Arctic conditions. Besides, the rutting season of reindeer begins in the autumn and lasts about a month. Only during this period is it possible to collect sperm as spermatogenesis in reindeer stops after rutting season. The aim of the work was to study the effects of cooling and freezing-thawing on the physiological and morphological traits of reindeer sperm quality. Reindeer sperm was collected by electric ejaculator or by washing out of the epididymis. After assessing the quality of ejaculated and epididymal semen (volume, total and progressive motility and sperm concentration), the sperm was diluted with Steridyl medium to a final concentration of 100 million/ml, packed in 0.25 ml straws and cooled to 5 °C for 120 min. After cooling and balancing, the straws were kept in liquid nitrogen vapors on a float at -110 °С for 12 min and then lowered into liquid nitrogen. Semen was thawed at 37 °C. The initial assessment of ejaculated sperm showed that the average volume of reindeer ejaculate was 0.5±0.08 ml, with concentration of 0.520±0.069 billion/ml, total motility of 64.3±4.07 %, and progressive motility of 47.9±4.24 %. The epididymal sperm cell concentration was on average 0.260±0.078 billion/ml, total and progressive motility was 43.6±8.49 % and 20.8±5.25 %, respectively. There was a large variability between ejaculates on the extent of changes in sperm motility after cryopreservation. Thus, total motility decreased by 41.9±5.38 % on average with fluctuations from 1 % to 89 %, progressive - by 36.8±5.29 % with fluctuations from 0 % to 75 %. A total of 42 % of ejaculates lost more than 50 % total motility. In some cases, there was a complete loss of motility after freezing, and in some samples the changes were insignificant. Large variability in changing cell motility was observed both in ejaculated and in epididymal semen. Epididymal sperm cells had higher motility after freezing than ejaculated spermatozoa, but showed more pronounced disturbances in the motility character. Sperm morphology analysis showed that there is an increased percentage with wrinkled or missing acrosome as compared to other animal species, i.e. 6.9±0.76 % in both ejaculated and epididymal reindeer sperm cells. There was no significant increase in damages of the sperm tail, neck and acrosome. The number of cells with injuries in tail and neck increased by 4.2±1.05 % with a range from 0.01 % to 15.7 %, and acrosome - by 2.5±0.35 with a range from 0.6 % to 8.3 %. High variability in the increase of plasma membrane damages was observed, i.e. 10.9±5.02 % with fluctuations from 0.13 % to 45 %. Such a large variability is due to the peculiarities of the reindeer sperm cryoresistance and differences between individual ejaculates. Significant difference in physiological and morphological changes in semen quality after cryopreservation between ejaculated and epididymal sperm were not found. Thus, the greatest changes in the cryopreserved reindeer semen are in motility and membrane integrity. The obtained data on physiological and morphological changes in reindeer semen during freezing should be taken into account when optimizing the composition of diluents and cryopreservation protocol.