Good Freezability Research Articles

88 SELECTION OF A CRYOSURVIVAL SPERM POPULATION DOES NOT IMPROVE THE IN VITRO PENETRATING ABILITY OF FROZEN - THAWED BOAR SPERMATOZOA

Boars can be classified as good or bad sperm freezers according to their sperm cryosurvival. Different sperm selection techniques, such as PureSperm� (PS; MidAtlantic Diagnostics, Inc., Mount Laurel, NJ, USA), have been developed to improve functional competence of spermatozoa. The aim of this experimental study was to assess the ability of PS for improving the in vitro penetrating ability of frozen–thawed boar spermatozoa from good and bad sperm freezers. The sperm-rich fractions from two boars, good (Boar A) and bad (Boar B) freezers, were extended in a lactose/eggyolk/ glycerol/Equex Stem (Noba Chemical Sales, Inc., Scituate, ME, USA) mixture (1 � 109 sperm mL–1), dispensed into 0.5-mL straws, and frozen using a programmable cell freezer. After thawing (1.200�C min–1), semen from each boar was split into two aliquots of 500 µL. One aliquot was used as the control. The second was placed into a tube of PS gradient (90%/45%) and centrifuged at 425g for 20 min; the pellet re-suspended in 1 mL of BTS and re-centrifuged at 320g for 10 min (PS sample). Control and PS samples were diluted in supplemented TCM-199 (TCMm; Roca et al. 1998 Reprod. Fertil. Dev. 10, 479–485) at 200 � 106 sperm mL–1. Sperm survival (SV) was assessed afterTCMm dilution according to progressive sperm motility (PSM, %) using a computer-assisted sperm analysis (CASA) system (ISAS�), and plasma and acrosome membrane integrity (PMI; %) by flow cytometry (SYBR�-14/PE-PNA/PI; Molecular Probes, Leiden, The Netherlands). A homologous in vitro penetration (hIVP) assay, using immature oocytes (20 oocytes/2 mL TCMm supplemented with caffeine and calcium lactate), was used to assess sperm penetrating ability (Martinez et al. 1993 Theriogenology 40, 547–557). A total of 960 immature oocytes were inseminated (200 � 103 sperm/oocyte) in 3 batches. After 18 h of co-incubation at 39�C under 5% CO2 in air, the oocytes were washed, mounted on slides, fixed with ethanol:acetic acid (3:1, v/v) for 48 h, stained with 1% lacmoid, and examined under a phase contrast microscope (�400). Oocytes with swollen or unswollen heads of sperm found in the vitellus were considered as penetrated. Sperm penetrability ability (SPA) was assessed according to penetration rate (PR) and the mean number of sperm per oocyte (S/O). Data were analyzed using a PROMIXED model and expressed as mean � SEM. Boar A showed better (P ≤ 0.01) results for both SV and SPA parameters than boar B, independent of sperm treatment. PureSperm improved (P ≤ 0.05) PSM and PMI in both boar A (control v. PS: 48.0 � 5.8 v. 66.5 � 3.6 and 63.1 � 7.7 v. 88.4 � 1.3, respectively) and boar B (12.3 � 1.2 v. 22.2 � 3.7 and 44.3 � 3.5 v. 58.7 � 7.0, respectively). However, no differences (P ≥ 0.05) were observed in PR and S/O in either boar A (71.2 � 3.4 v. 78.3 � 3.1 and 5.0 � 0.4 v. 5.2 � 0.4, respectively) or boar B (34.3 � 3.6 v. 37.3 � 3.9 and 1.5 � 0.1 v. 1.5 � 0.1, respectively). In conclusion, under our laboratory conditions, PureSperm selection improves sperm quality but not in vitro penetrating ability of frozen–thawed spermatozoa of both good and bad sperm freezers. This work was supported by CICYT (AGF2005-00760), Madrid, Spain.

97 DIFFERENCES IN SPERM CHROMATIN STRUCTURE AMONG GOOD AND BAD BOAR SPERM FREEZERS

Inter- and intra-boar differences in sperm freezability are observed independent of the sperm quality before freezing, the breed, or the genetic line. This study aimed to determine whether boars with different post-thaw sperm quality also show differences in sperm DNA integrity. Sperm-rich fractions (3 to 10 ejaculates per boar) from 19 fertile mature boars were extended in Beltsville thawing solution (BTS) and cooled to 17�C for 16 h. Then, samples were centrifuged at 2400g for 3 min, extended in freezing extender (lactose/egg yolk/glycerol/Equex STM; Nova Chemical Sales, Inc., Scituate, MA, USA) to a final concentration of 1 � 109 spermatozoa/mL, dispensed into 0.5 mL straws, and frozen in a programmable cell freezer at a rate of -20�C min. Thawing was carried out in a water bath at 37�C for 20 s. Frozen-thawed spermatozoa were evaluated for progressive sperm motility (PSM) using a computer-assisted sperm analysis (CASA) system, and sperm viability (PMI) using flow cytometry. All data generated were used for a multivariate pattern analysis (PATN; CSIRO, Canberra, Australia) which objectively classified all boars into two groups, categorized as good (n = 10; >60% PSM and PMI) or bad (n = 9; <40% PSM and PMI) based on their sperm freezability. Post-thaw sperm quality was consistent for different ejaculates within boars (P < 0.05). The DNA-integrity of frozen-thawed spermatozoa was evaluated according to the sperm chromatin structure assay (SCSA; Evenson et al. 1980 Science 210, 1131-1133). All SCSA variables (X mean, DNA fragmentation index (DFI), and the standard deviation of the DFI), were significantly higher for bad freezers (P < 0.001). The percentage of spermatozoa with abnormal chromatin structure ranged from 1.06 to 3.42% for good and 3.06 to 6.04% for bad freezers. Although these differences exist between good and bad sperm freezers, and can only to some extent be the product of cryopreservation, the levels of affected spermatozoa can not explain the differences on post-thaw sperm survival seen in the two categories of sires. This work was supported by CICYT, AGL05-0471 (Spain), SLF and Formas (Sweden).

Effects of glutamine on post-thaw motility of stallion spermatozoa: an approach of the mechanism of action at spermatozoa level

The cryoprotective effect of l-glutamine and an approach of its mechanism of action, in preserving motility of stallion spermatozoa during the freezing-thawing process, were studied. In Experiment 1, thirty-six ejaculates were collected from six stallions (two good, two middle, and two of poor sperm freezability) and were diluted with 10 different freezing media derived from INRA 82 medium supplemented with 20 mM HEPES and 2% (v/v) centrifuged egg yolk (BM). After thawing, sperm motility was evaluated by a computer-assisted semen motility analyser. The effects of glutamine and glycerol at different concentrations on post-thaw sperm motility were studied. A possible interaction between medium and semen freezability was investigated. Only the 50 mM glutamine + 2.5% glycerol medium significantly improved sperm motility compared to classical freezing medium (2.5% glycerol). The presence of glutamine at 50 mM was not sufficient to offset the need to use glycerol in the freezing extender. The use of glutamine at a higher concentration >100 mM in the presence of 2.5% of glycerol was toxic. Reducing the glycerol proportion from 2.5% to 2 or 1.5% in the presence of glutamine at 50, 75, and 100 mM had no influence on post-thaw motility of semen of middle and good freezability. Moreover, the substitution of 2.5% glycerol by 50 mM glutamine in BM, did not significantly change the post-thaw motility of semen of good freezability. In Experiment 2, 3 H -glutamine and 3 H -glycerol were used to study the kinetics of penetration of glutamine and glycerol in sperm cells. The radioactivity of each radio-labelled semen pellet was measured at different times (0, 15, 30, 60, 90, 120 min), by using a Packard tri-carb 4530 apparatus. The percentages of incorporated radioactivity (%IRA) in semen pellets were calculated at different times. The %IRA of 3 H -glycerol in semen pellets were significantly higher than the %IRA of 3 H -glutamine. The %IRA of 3 H -glycerol in semen pellets increased greatly from time 0 to 60 min, and then it is stabilized from 60 to 120 min. In contrast, the %IRA of 3 H -glutamine in semen pellets increased slightly from 0 to 60 min, then it stabilized until 120 min. These experiments demonstrate that glutamine has a synergistic cryoprotective effect with glycerol on cryopreservation of stallion spermatozoa, and suggest that glutamine acts at the extra-cellular level, independently of glycerol.

92THE ADDITION OF SEMINAL PLASMA FROM INDIVIDUAL BOARS TO FREEZING EXTENDER CAN IMPROVE THE POST-THAW SPERM SURVIVAL

Contradictory results have been reported about the effect of seminal plasma (SP) on the freezability of mammalian spermatozoa. In pigs, current methods for sperm cryopreservation involve removing seminal plasma. Therefore, no conclusive evidence of the potential effect of SP on the freezability of boar spermatozoa has been reported. In this study, we evaluate the effect of the addition of low concentrations of SP from individual boars to the freezing extender on post-thaw sperm survival. Sperm cryopreservation procedure included: dilution of sperm-rich fraction in Beltsville Thaw Solution extender (BTS), cooling to 17°C for 16h, centrifugation at 2400g for 3min, dilution in lactose/egg-yolk/glycerol/Equex Stem (freezing extender) to a final concentration of 1×109 spermmL−1, dispensing into 0.5-mL straws, and freezing in a programmable cell freezer at 20°Cmin−1. Thawing was carried out in a waterbath at 37°C for 20s. Post-thaw sperm survival was assessed by progressive sperm motility (PSM) using a CASA system (SCA); plasma membrane integrity (PMI) and acrosome membrane integrity (AMI) were assessed by flow cytometric procedures (SYBR-14/PI and FITC-PNA/PI, respectively) at 30 and 150min post-thawing in BTS-diluted thaw spermatozoa held in a waterbath at 37°C. Four individual seminal plasma donors (SP1 to SP4) were selected in a preliminary study in which 48 ejaculates from 12 boars (4 ejaculates/boar) were cryopreserved. Then the boars were classified into 3 groups (good, moderate and bad freezers) based on their post-thaw sperm survival. SP1 and SP2 were good freezers (>60% PSM and PMI), SP3 was a moderate freezer (40–60% PSM and PMI) and SP4 was a bad freezer (<40% PSM and PMI). In the main experiment, pooled sperm-rich fractions collected from 9 mature hybrid boars were divided into five aliquots and each was diluted with freezing extender supplemented with 0% (control) or 10% of SP (1–4). Data from eight replicates were analyzed as a split plot design using a PROMIXED model. The addition of SP to freezing extender had a significant effect (P<0.05) on post-thaw sperm survival compared to control. Moreover, there were significant differences (P<0.05) between SP donors. PSM, PMI and AMI were significantly (P<0.05) higher in SP1 (56.71±4.30; 57.16±4.01 and 57.22±4.01, respectively) and SP2 (59.48±4.30; 60.17±4.01 and 60.05±4.01, respectively) compared to control (50.39±4.30; 49.98±4.01 and 49.54±4.01, respectively). There were no differences (P>0.05) between SP3, SP4 and control. These results indicate that the addition of SP from particular boars (good freezers) to freezing extender may improve post-thaw sperm survival. Individual differences in the SP composition should explain the above results. Supported by INIA (RZ01-019) and MCYT (AGL2001-0471).

Influence of exogenous GnRH on sexual behavior and frozen/thawed semen viability in stallions during the non-breeding season

Twelve fertile stallions were divided into two groups, either receiving gonadotropin-releasing hormone (GnRH) ( n=6) or Placebo ( n=6). Based on the history of frozen/thawed semen characteristics three stallions within each group were assigned as being “good freezers” [GnRH (+); Placebo (+)] and three stallions were assigned as being “poor freezers” [GnRH (−); Placebo (−)]. The study was performed as a “blinded” investigation and stallions were treated twice daily by an intramuscular injection of 1 ml GnRH (Buserelin ®, 50 μg) or Placebo. The experiment was divided into three time periods. Period A (pre-treatment) was performed between 16 November and 20 December; Period B (treatment) was performed during 6 weeks between 21 December and 31 January; and Period C (post-treatment) was performed between 1 February and 12 February. Semen was collected every Monday, Wednesday, Friday, and analysed for motion characteristics by the use of a computerized semen analyser, and sperm morphology immediately after collection. The spermatozoa were cryopreserved, stored in liquid nitrogen, and evaluated for motility (computer assisted semen analysis), membrane integrity (carboxyfluoresceine diacetate (CFDA) combined with propidium-iodide (PI), CFDA/PI), viability and sperm morphology (Eosine–Nigrosine, EN), and osmotic reactivity (hypo-osmotic swelling test, HOS) following thawing in a water bath. The viability of spermatozoa was expressed as the difference between pre-freeze and post-thaw values. A libido score of 1–4, the number of mounts on the phantom before ejaculation, and ejaculation latency were used to evaluate the stallions sexual behavior. Effect of treatment was analysed by comparing time intervals within groups as well as comparing groups within time intervals using SAS statistics software. GnRH treatment decreased the number of mounts before ejaculation (GnRH (total): 2.5±1.14 versus 1.8±1.06, P<0.05), and shortened ejaculation latency. Cessation of treatment increased ejaculation latency in the GnRH group (4.7±4.98 min versus 7.2±7.88 min, P<0.05). With the exception of libido score all parameters of sexual behavior were superior in the GnRH (+) group compared to the Placebo (−) group during the treatment period ( P<0.05). GnRH administration increased progressive motility (GnRH (+): 30.7±10.74% versus 38.4±15.1%, P<0.05; GnRH (total): 24.9±11.80% versus 31.9±14.68%, P<0.05), membrane intact spermatozoa CFDA/PI (GnRH (−): 16.8±7.17% versus 26.2±7.02%, P<0.05; GnRH (total): 23.1±12.33% versus 29.5±10.77%, P<0.05) and HOS positive spermatozoa (GnRH (+): 33.2±11.29% versus 42.2±10.36%, P<0.05; GnRH (total): 32.9±10.23% versus 40.1±10.30%, P<0.05) of frozen/thawed spermatozoa. Following cessation of treatment, the viability of frozen/thawed spermatozoa decreased. GnRH treated stallions had lower losses of live stained spermatozoa (EN) compared to the Placebo group (GnRH (total): 17.6±4.77 versus Placebo (total): 27.2±5.44, P<0.05). This was particularly observed in the “poor freezer” group (GnRH (−): 16.6±4.35 versus Placebo (−): 31.3±5.87; P<0.05). In conclusion, exogenous GnRH was shown to improve sexual behavior and increase the quality of frozen/thawed spermatozoa in fertile stallions during the non-breeding season. Nevertheless, it seems that, although significance was achieved relative to improvement to post-thaw sperm quality, that the “real” change in sperm quality seems negligible in fertile stallions. The mechanism of GnRH effect was not determined but this study may support the possibility of a direct gonadal or epididymal effect of exogenous GnRH in the stallion.

Glycine betaine improves survival of fresh bovine spermatozoa.

Fresh spermatozoa from bulls established as 'good freezers' and 'poor freezers' (consistently > or = 50% or < 20% motile spermatozoa after cryopreservation, respectively) were incubated for 96 h in Tes/Tris-egg yolk or TALP-egg yolk media at 37 degrees, 20 degrees , 5 degrees or 0 degrees C. The TALP extender contained 0, 100 or 200 mM glycine betaine (GB) to test the hypothesis that GB would efficiently maintain spermatozoa function during long-term incubation. The percentage of motile spermatozoa declined over time in a temperature- and medium-dependent fashion. No spermatozoa were motile by 24 h incubation at 37 degrees C or by 72 h incubation at 0 degrees C, and there were no significant differences in the percentage of motile spermatozoa from either category of bull when spermatozoa were incubated in any media for less than 24 h. Spermatozoa from poor freezers were significantly more motile than spermatozoa from good freezers after 96 h at 20 degrees or 5 degrees C in TALP alone; however, GB at both 100 and 200 mM increased the percentage of motile spermatozoa in poor and good freezers and eliminated these differences. Overall, the presence of GB at either 100 or 200 mM significantly improved the percentage of motile spermatozoa at 20 degrees, 5 degrees and 0 degrees C, but not at 37 degrees C.

Fertility of Deep Frozen Boar Spermatozoa

In the present investigation the results of two insemination trials with deep frozen boar spermatozoa are presented. The aim of the trials was to study the effect of different thawing diluents and to compare the fertility of deep frozen spermatozoa from four boars. The trials utilized a total of 139 gilts. The thawing diluents used were boar seminal plasma, protein free seminal plasma, the thawing diluent OLEP and isotonic glucose solution. The composition of OLEP was based on physical and biochemical analyses of boar seminal plasma. The electrolyte levels, pH and osmotic pressure of OLEP are similar to those of boar seminal plasma. From the results it is evident that thawing in boar seminal plasma, protein free seminal plasma and OLEP yielded equal results. Thawing in isotonic glucose solution yielded significantly poorer results concerning percentage of fertilized ova 24–48 hrs. after insemination and almost significantly poorer fertility results four weeks after insemination. The possible effects of the thawing diluents are discussed. With the freezing procedure applied, electrolyte levels, pH and osmotic pressure seem to be factors of importance for the survival of the frozen and thawed spermatozoa and for the maintenance of their fertilizing capacity. Almost significant differences were found in fertility of spermatozoa from different boars. These differences were reflected in pregnancy rates as well as ratio of foetuses to c. 1. in pregnant gilts. The differences were found to be independent of thawing diluent. The variation seems to be caused by differences in resistance of the spermatozoa to the freezing and thawing procedure. The need for laboratory methods for selection of boars with spermatozoa of good freezability is stressed.