S. Borragan

Effect of basic factors of extender composition on post-thawing quality of brown bear electroejaculated spermatozoa

The improvement of freezing extenders is critical when defining sperm cryopreservation protocols for wild species, in order to create germplasm banks. The aim of this study was to evaluate the effect of additives (Equex Paste and EDTA) supplementation, egg-yolk (10 and 20%) and glycerol (4 and 8%) concentrations and extender osmolality (300 and 320 mOsm/kg) on the post-thawing quality of brown bear semen. Semen was obtained from 20 adult males by electroejaculation, and centrifugated individually (600 x g for 6 min). The pellets were diluted 1:1 in the corresponding extender TTF (TES-Tris-Fructose with the aforementioned variants) and cooled to 5 degrees C. Then, it was diluted down to 100 x 10(6) spz/mL, loaded in 0.25 mL straws and frozen at -20 degrees C/min. After thawing (in water at 65 degrees C for 6s), the semen samples were assessed for motility (CASA), viability (SYBR-14 with propidium iodide), acrosomal status (PNA-FITC with propidium iodide) and mitochondrial activity (JC-1). Extender supplementation with additives rendered significantly higher results for these sperm parameters. Comparing the two percentages of egg yolk, 20% egg yolk showed the highest motility results, percentages of viable spermatozoa and viable spermatozoa with intact acrosome. No differences were detected among samples frozen using 4 or 8% glycerol. For extender osmolality, 300 mOsm/kg showed higher values of VAP, VCL, VSL, and ALH than 320 mOsm/kg. Based on the best performance of sperm motility, viability and acrosome status, we conclude that the most suitable extender to cryopreserve brown bear spermatozoa was TTF adjusted to 300 mOsm/kg, supplemented with 20% egg yolk, 4-8% glycerol, and the additives 1% Equex paste and 2% EDTA.

Effects of cryopreservation on head morphometry and its relation with chromatin status in brown bear (Ursus arctos) spermatozoa

The Cantabrian brown bear (Ursus arctos) is a highly endangered species in Spain and basic studies are necessary in order to bank its germplasm. Sperm heads are mainly made up of chromatin, thus their shape depends partly on chromatin structure. Thawed semen from 10 bears was used to analyze chromatin status by sperm chromatin structure assay (SCSA) and head morphometry by the computer-assisted sperm morphology assessment (CASMA) system. Morphometry was analyzed before and after freezing-thawing in order to evaluate the effects of cryopreservation on sperm heads. Each spermatozoon was measured for four primary parameters (length, L; width, W; area, A; perimeter, P) and derived parameters (ellipticity: L/W, circularity: 4piA/ P2, elongation: (L-W)/(L+W), regularity: piLW/ 4A). All the derived parameters significantly differed between bears. Likewise, cryopreservation affected head morphometry by reducing its size. Clustering based on morphometric parameters separated three subpopulations, one of them being significantly more influenced by the cryopreservation process. We obtained high correlations between head morphometry and SCSA parameters: standard deviation of DNA fragmentation index (SD-DFI) was correlated with perimeter and area (r=0.75 and r=0.62, respectively) and DFIm and DFIt (moderate and total DNA fragmentation index) were correlated with perimeter (r=0.65 and r=0.67, respectively). Nevertheless, classification of males according to SCSA or head morphometry did not completely agree so the two assays might explain male variability differently. We conclude that cryopreservation affected morphometry at least in a subset of spermatozoa. These results might improve future application of sperm banking techniques in this species.

Sperm cryopreservation in brown bear (Ursus arctos): preliminary aspects.

The development of sperm cryopreservation procedures in brown bear is the basis for establishing a specific genetic resource bank aimed at the preservation of a Cantabric brown bear population, which is seriously threatened. Several issues complicate the development of these cryopreservation procedures: lack of previous specific studies, a high incidence of urospermia and spermagglutination observed in bear ejaculates. Moreover, the availability of individuals for research from these threatened populations is problematic. In the case of the Cantabric brown bear, we have used males from other populations, but of the same species, as surrogates, to carry out a direct extrapolation of the results. Urospermia-- Moreover, 70% of the ejaculates are urine contaminated and spermagglutination have a detrimental effect on post-thawing cell quality recovery in this species. Considering the high value of these samples (autochthonous population with few individuals), a pre-selection of the ejaculates is not a viable alternative. Preventive methods reducing the mentioned detrimental effects need to be developed. On the basis of previous data, we can suppose that bear spermatozoa resist freezing injuries well. Nevertheless, because of the scarcity of this information, it is necessary to conduct further research on bear semen freezing under field conditions. Epidydimal spermatozoa can be important for genetic resource banking of threatened populations and thus specific cryobiological protocols need to be assayed. To date, 168 brown bear ejaculates have been frozen by the ITRA-ULE group at the University of León (Spain) in the development of methodologies for the preservation of brown bear sperm.

Optimization of Glycerol Concentration and Freezing Rate in the Cryopreservation of Ejaculate From Brown Bear (Ursus arctos)

In order to establish a semen bank for the endangered Cantabrian brown bear, we tested five glycerol concentrations and three freezing rates for electroejaculated semen. Electroejaculation was performed on nine males. Semen was diluted in TES-Tris-Fructose (20% egg yolk, 2% EDTA, 1% Equex) with 2%, 4%, 6%, 8% or 10% glycerol and frozen at -10, -20 or -40°C/min. Before and after cryopreservation, samples were analysed for motility (CASA), viability and acrosomal status (flow cytometry). Pre-freezing results showed that glycerol concentration had no significant effect on total motility or progressive motility, but it significantly decreased VCL, ALH, viability and acrosomal status (p < 0.05). After thawing, sperm motility was higher at extender with 4%, 6% and 8% glycerol, but only at 4% and 6% glycerol for viability and acrosomal status. For 4% and 6% glycerol, freezing rates did not have significant effects. The curve fitting gave an estimate of the optimal glycerol concentration, with all the optimal values for every parameter between 6% and 7% glycerol falling. We propose using 6% glycerol and a freezing velocity of -20°C/min for freezing brown bear ejaculated spermatozoa.

Quality of frozen-thawed semen in brown bear is not affected by timing of glycerol addition.

We have tested several freezing protocols for brown bear semen, modifying the time when glycerol was added (before and after cooling to 5 °C). No differences were found among protocols, indicating a good tolerance of brown bear semen to glycerol. This finding indicates that freezing protocols for brown bear semen could be modified to fit practical solutions which would facilitate preparation of the seminal samples in the field with the addition of glycerol at ambient temperature.

The antioxidant effects of soybean lecithin- or low-density lipoprotein-based extenders for the cryopreservation of brown-bear (Ursus arctos) spermatozoa

Egg yolk low-density lipoproteins (LDL) and soybean lecithin were evaluated as replacements for egg yolk in extenders used for the cryopreservation of brown-bear spermatozoa. The motility, viability and acrosomal status of post-thawed spermatozoa were analysed, and an egg-yolk extender was used as a control. The total antioxidant capacity of these extenders was tested. Soybean lecithin showed an effect that was dependent on the soybean concentration (2%, 3.5% and 5%) and source (Type A: 24% L-α-phosphatidylcholine, and Type B: 14-23% L-α-phosphatidylcholine). Only semen cryopreserved with 5% Type A soybean exhibited a sperm motility similar to that of semen cryopreserved in egg-yolk-based extender after thawing, although the sperm viability and acrosome status were not as high. Semen frozen in an extender containing LDL (10-15%) exhibited improved sperm viability in comparison with the control, but sperm motility was lower. The LDL-based extender exhibited a higher anti-oxidant activity than the egg-yolk extender and soy lecithin-based extenders. The extenders with higher anti-oxidant activity showed improvements in frozen sperm viability but lower semen motility. These results indicate that soybean lecithin did not have the same protective effect as egg yolk during the freezing of brown-bear spermatozoa but suggest that LDL (10-15%) could be a useful substitute for egg yolk in these extenders.

Effect of colloid (Androcoll-Bear, Percoll, and PureSperm) selection on the freezability of brown bear (Ursus arctos) sperm.

The development of a species-specific conservation protocol that involves artificial insemination with frozen semen needs to validate an effective methodology for freezing semen. Colloid centrifugation has been suggested and widely applied as an effective tool for selecting animal spermatozoa for artificial breeding. The objective of the present study was to compare different methods of centrifugation, single layer using Androcoll-Bear and Percoll and double layer using PureSperm 100 (in two different discontinuous gradients 40%-80% and 45%-90%), for the selection of fresh brown bear sperm samples. In the before freezing group, all selected samples showed a higher progressive motility and viability (except Percoll for motility 43.0 ± 5.3 [P < 0.05]); all colloids except PureSperm 45/90% rendered samples with fewer damaged acrosomes. In the after thawing group, all tested centrifugation colloids showed a good capacity to decrease the number of damaged acrosomes. Furthermore, PureSperm treatment (45/90%) resulted in an increase in apoptotic-like changes not only immediately after thawing but also after the incubation test, leading us to suggest that this gradient could induce some kind of deleterious effects on the sperm samples. On the other hand, PureSperm treatment (40/80%) yielded a quality preservation capacity similar to Androcoll-Bear in number of damaged acrosomes, different relative to the control (control, 5.3 ± 0.6; PureSperm 80, 2.0 ± 0.3; Androcoll, 2.1 ± 0.9 [P < 0.05]) but a decrease in the number of viable spermatozoa recovered after thawing relative to the control (control, 21.2 ± 3.1; PureSperm 80, 13.7 ± 2.7 [P < 0.05]). In conclusion, Androcoll-Bear constitutes a useful tool for handling of brown bear ejaculates owing to its simple handling and procedure with a reliable sperm selection and freezability. This colloid yielded an improvement in several sperm parameters in brown bear frozen-thawed semen; the selected spermatozoa of fresh samples with this colloid showed a better resistance to freezing compared with the control sample not only for motility but also for viability.

Brown bear sperm double freezing: Effect of elapsed time and use of PureSperm gradient between freeze-thaw cycles

The use of sexed spermatozoa has great potential to captive population management in endangered wildlife. The problem is that the sex-sorting facility is a long distance from the semen collection place and to overcome this difficulty two freeze-thaw cycles may be necessary. In this study, effects of refreezing on brown bear electroejaculated spermatozoa were analyzed. We carried out two experiments: (1) to assess the effects of the two freezing-thawing cycles on sperm quality and to analyze three different elapsed times between freezing-thawing cycles (30, 90 and 180 min), and (2) to analyze the use of PureSperm between freezing-thawing cycles to select a more motile and viable sperm subpopulation which better survived first freezing. The motility, viability and undamaged acrosomes were significantly reduced after the second thawing respect to first thawing into each elapsed time group, but the elapsed times did not significantly affect the viability and acrosome status although motility was damaged. Our results with the PureSperm gradient showed higher values of viability in freezability of select sample (pellet) respect to the rest of the groups and it also showed a significant decrease in the number of acrosome damaged. In summary, the double freezing of bear semen selected by gradient centrifugation is qualitatively efficient, and thus could be useful to carry out a sex-sorting of frozen-thawed bear spermatozoa before to send the cryopreserved sample to a biobank. Given the low recovery of spermatozoa after applying a selection gradient, further studies will be needed to increase the recovery rate without damaging of the cell quality.

Use of commercial extenders and alternatives to prevent sperm agglutination for cryopreservation of brown bear semen

The objective of this study was to evaluate different bovine and canine commercial semen extenders for cryopreservation of brown bear ejaculates and the effect of semen collection directly into extender on sperm agglutination. Semen samples were obtained by electroejaculation from 13 adult males. In experiment 1, eleven ejaculates from eight bears were used to evaluate Bioxcell and Andromed as extenders, whereas in experiment 2, nine ejaculates from six bears were used to evaluate Triladyl canine, CaniPro, and Extender 2 as extenders. An extender specifically developed for brown bears (Test-Tris-fructose-egg yolk-glycerol, TTF-ULE/bear) served as a control extender in both experiments. After thawing, total and progressive sperm motility and sperm viability were greater (P < 0.05) for TTF-ULE/bear and Andromed extenders than for Bioxcell in experiment 1 and greater (P < 0.05) for TTF-ULE/bear extender than for Triladyl Canine, CaniPro, and Extender 2 in experiment 2. In experiment 3, addition of handling extender (TTF-H) to the semen collection tube for eight ejaculates from seven bears resulted in less (P < 0.05) sperm agglutination in fresh samples (score 0.5 ± 0.2 vs. 1.8 ± 0.4 in diluted and control samples, respectively) with no effect on pre-freeze and post-thawing semen quality. In conclusion, TTF-ULE/bear is the most suitable extender for brown bear semen cryopreservation, but comparable results can be obtained with the commercial extender Andromed. In addition, collection of ejaculates directly in TTF-H extender decreases sperm agglutination in fresh samples.

Tolerance of brown bear spermatozoa to conditions of pre-freezing cooling rate and equilibration time

Specific protocols for the cryopreservation of endangered Cantabrian brown bear spermatozoa are critical to create a genetic resource bank. The aim of this study was to assess the effect of cooling rates and equilibration time before freezing on post-thawed brown bear spermatozoa quality. Electroejaculates from 11 mature bears were extended to 100 × 10(6) spermatozoa/mL in a TES-Tris-Fructose-based extender, cryopreserved following performance of the respective cooling/equilibration protocol each sample was assigned to, and stored at -196 °C for further assessment. Before freezing, after thawing, and after 1 hours incubation post-thawing at 37 °C (thermal stress test), the quality of the samples was assessed for motility by computer-assisted semen analysis, and for viability (SYBR-14/propidium iodide), acrosomal status (peanut agglutinin-fluorescein isothiocyanate /propidium iodide), and sperm chromatin stability (SCSA) by flow cytometry. In experiment 1, three cooling rates (0.25 °C/min, 1 °C/min, and 4 °C/min) to 5 °C were assessed. After thawing, total motility (%TM) was higher and percentage of damaged acrosomes (%dACR) was lower (P < 0.05) for 0.25 °C/min than for 4 °C/min. The thermal stress test data indicated equally poor quality (P < 0.05) for the 4 °C/min cooled samples in viability (%VIAB), %dACR, %TM, and progressive motility (%PM). In experiment 2, the effect of a pre-freezing equilibration period at 5 °C for 1 hour (cooling at 0.25 °C/min) was evaluated. Samples kept at 5 °C for 1 hour showed higher (P < 0.05) values than the nonequilibrated ones for both thawing (%dACR) and thermal stress test (%VIAB, %TM, and %PM). In experiment 3, samples stored without cooling and equilibration (direct freezing) were compared with the samples cooled at 0.25 °C/min and equilibrated for 1 hour (control freezing). Using thermal stress test, we observed that direct freezing causes damage in viability, acrosomal status, and motility of spermatozoa compared with the control group (P < 0.05). In conclusion, our results suggest that slow cooling rates to 5 °C and at least 1 hour equilibration time are necessary for the effective cryopreservation of brown bear sperm.