A comparative study of the effects of freezing and frozen storage on intact and demembranated bull spermatozoa

Sperm survival kinetics in different types of bull semen: progressive motility, plasma membrane integrity, acrosomal status and reactive oxygen species generation

This study was designed to compare the kinetics of sperm survival in different types of bull semen. Fresh ejaculates from four bulls were pooled, diluted in Tris-citric acid-egg yolk-glycerol extender, cooled to 4°C, frozen in LN2 and thawed at 37°C. Fresh, diluted, cooled and frozen–thawed semen were incubated at 37°C, and evaluated at 0, 2, 4, 6, 12 and 24 h after the beginning of incubation. In Experiment 1, progressive sperm motility, normal acrosomes and plasma membrane integrity and asymmetry were determined. In Experiment 2, generation of superoxide anion (O2•) along with plasma membrane permeability and generation of hydrogen peroxide (H2O2) along with plasma membrane integrity were assessed. In Experiment 1, frozen–thawed semen had shorter survival times for progressive sperm motility, and spermatozoa with intact plasma membranes and acrosomes (IPM-IACR) as compared with other types of semen (P < 0.05). Fresh spermatozoa underwent a necrotic pathway, diluted and cooled spermatozoa underwent an apoptosis-like pathway and frozen–thawed spermatozoa underwent both necrotic and apoptosis-like pathways. In Experiment 2, spermatozoa in all four types of semen exhibited O2•– generation and increased plasma membrane permeability, and became necrotic without H2O2 generation during incubation (P < 0.05). In conclusion, frozen–thawed semen had shorter sperm longevity, which has important implications relating to the timing of artificial insemination. Different types of semen followed different death pathways. During incubation, spermatozoa in all types of semen generated O2•–, which increased the permeability and compromised the integrity of the plasma membrane.

Ram Sperm Selection by a Dextran/Swim-Up Procedure Increases Fertilization Rates Following Intrauterine Insemination in Superovulated Ewes

The objective of this study was to compare the efficacy of 2 dextran/swim-up media to increase the sperm quality parameters and the maintenance of these parameters at 15 degrees C and 30 degrees C over 6 hours. Additionally, this study examined whether differences in sperm quality reflect different reproductive efficiencies following intrauterine insemination in superovulated ewes. The study involved 2 selected samples (SS) obtained by dextran/swim-up, performed either with (SS+) or without (SS-) capacitating compounds, and a control sample consisting of raw semen diluted in the same medium. The efficacies of the swim-up sperm selection procedures were similar in both media, and no significant differences were found among the evaluated parameters. Conversely, we found important differences between selected and control samples. Sperm motility, viability (as assessed by carboxifluorescein diacetate/propidium iodide [PI] staining), and mitochondrial activity (as assessed by rhodamine 123/PI) were significantly higher in the selected samples than in the control. Additionally, following incubation at 15 degrees C, the preservation of sperm quality was significantly better in the selected samples than in the control samples. After 6 hours of incubation at 15 degrees C, selected samples had a motility value of 46%, which was significantly (P < .001) higher than the value observed in control samples (27%). The percentage of viable cells observed after 6 hours of incubation at 15 degrees C was significantly (P < .0001) higher in selected samples than in the control samples. Furthermore, after 2 hours of incubation at 30 degrees C, swim-up samples had viability values that were significantly (P < .0001) higher than those of the control samples. SS+ and SS- samples did not differ significantly in spermatozoa yield, sperm quality, or survival. Differences between selected samples and controls were reflected in the fertilization rate obtained following intrauterine insemination in superovulated ewes that experienced a 52-hour interval between progestagen removal and artificial insemination. A restricted criterion for fertilization rate evaluation was established, and only the percentage of embryos recovered from the uterine horns 6 days after insemination was considered with respect to the total number of corpora lutea counted in the ovaries. The fertilization rate of SS- samples (50%) was significantly higher (P > .001) than those of the SS+ (2%) and control samples (5%).

A comparative study of Sephadex, glass wool and Percoll separation techniques on sperm quality and IVF results for cryopreserved bovine semen

The aim of this study was to compare the effects of spermatozoa separation techniques on sperm quality and in-vitro fertilization (IVF) results for cryopreserved bovine semen. Sephadex, glass wool and Percoll gradient separation techniques were used for sperm separation and sperm motility, morphology and membrane integrity were evaluated before and after separation. Also, cleavage and blastocyst developmental rate were investigated after IVF with sperm recovered by each separation technique. The motility of samples obtained by the three separation techniques were greater compared to the control samples (p < 0.05). The percentage of spermatozoa with intact plasma-membrane integrity, identified by 6-carboxyfluoresceindiacetate/propidium iodide fluorescent staining and the hypo-osmotic swelling test, was highest in the glass wool filtration samples (p < 0.05). The cleavage and blastocyst rate of total oocytes produced from glass wool filtration samples were also higher than the control and Sephadex filtration samples (p < 0.05), but were not significantly different from Percoll separation samples. However, a significantly greater number of cleaved embryos produced by glass wool filtration developed to blastocyst stage than those produced by Percoll separation (p < 0.05). These results indicate that spermatozoa with good quality can be achieved by these three separation techniques and can be used for bovine IVF. In particular, it suggests that glass wool filtration would be the most effective method of the three for improving sperm quality and embryo production for cryopreserved bovine spermatozoa.

Effects of filtration of semen doses from subfertile boars through neuter Sephadex columns

This study was designed to develop a method of improving the quality of sperm obtained from subfertile Piétrain boars. Seminal doses were filtered through neuter Sephadex columns (G-25 Medium, G-50 Fine, G-50 Medium and G-75, length 10 +/- 0.5 cm, flow rate 1 ml/20 s). Doses were prepared by pooling 10 ml semen samples collected from 58 asthenoteratospermic boars and diluted the sperm-cell rich fraction 1 : 6 in Betsville thawing solution extender. Sperm quality was determined before and after the filtering process. Sperm morphology and motility were assessed using the computer program SCA 2002 production, and sperm vitality was evaluated by fluorescence multistaining. ORT and HRT tests were used to determine the osmotic resistance of spermatozoa, and metabolic performance was assessed by measuring l-lactate production. Results indicate that the filtration process rendered increased proportions of mature spermatozoa and of viable spermatozoa with an intact acrosome, nucleus and mitochondrial sheath. Sperm filtration led to decreased percentages of spermatozoa with proximal and distal droplets and of agglutinated spermatozoa, along with slightly diminished ORT values. HRT scores and L-lactate production were unaffected. Our findings indicate that filtering through a Sephadex column improves the sperm morphology and vitality of seminal doses obtained from subfertile boars, but produces no functional changes in the spermatozoa. All four column types yielded similar results.

Retained Functional Integrity of Bull Spermatozoa after Double Freezing and Thawing Using PureSperm® Density Gradient Centrifugation

The main aim of this study was to compare the motility and functional integrity of bull spermatozoa after single and double freezing and thawing. The viability and morphological integrity of spermatozoa selected by PureSperm density gradient centrifugation after cryopreservation of bovine semen in two commercial extenders (Experiment 1) and the function of bull spermatozoa before and after a second freezing and thawing assisted by PureSperm selection (Experiment 2) were examined. On average, 35.8 +/- 12.1% of sperm loaded onto the PureSperm density gradient were recovered after centrifugation. In Experiment 1, post-thaw motility and acrosome integrity were higher for spermatozoa frozen in Tris-egg yolk extender than in AndroMed, whether the assessments were made immediately after thawing [80.4 +/- 12.7 vs 47.6 +/- 19.0% motile and 78.8 +/- 8.3 vs 50.1 +/- 19.5% normal apical ridge (NAR), p < 0.05] or after preparation on the gradient (83.3 +/- 8.6 vs 69.4 +/- 15.9% motile and 89.5 +/- 7.2 vs 69.1 +/- 11.4% NAR, p < 0.05). For semen frozen in Tris-egg yolk extender, selection on the PureSperm gradient did not influence total motility but significantly improved the proportion of acrosome-intact spermatozoa. After the gradient, both the total motility and percentage of normal acrosomes increased for spermatozoa frozen in AndroMed (Minitüb Tiefenbach, Germany). In Experiment 2, there was no difference in sperm motility after the first and second freeze-thawing (82.9 +/- 12.7 vs 68.8 +/- 18.7%). However, the proportion of acrosome-intact spermatozoa was significantly improved by selection through the PureSperm gradient, whether measured by phase contrast microscopy (78.9 +/- 9.7 vs 90.4 +/- 4.0% NAR, p < 0.05) or flow cytometry (53.4 +/- 11.7 vs 76.3 +/- 6.0% viable acrosome-intact spermatozoa, p < 0.001). The improvement in the percentage of spermatozoa with normal acrosomes was maintained after resuspension in the cooling extender and cooling to 4 degrees C (88.2 +/- 6.2) and after re-freezing and thawing (83.6 +/- 6.56% NAR). However, flow cytometric assessment of the sperm membranes revealed a decline in the percentage of viable spermatozoa with intact membranes after the second freezing and thawing compared with after gradient centrifugation (76.3 +/- 6.0% vs 46.6 +/- 6.6%, p < 0.001) to levels equivalent to those obtained after the first round of freeze-thawing (53.4 +/- 11.7% viable acrosome-intact spermatozoa). Sperm movement characteristics assessed by computer-assisted analysis were unaffected in the population selected on the PureSperm gradients but declined after cooling of the selected and extended spermatozoa to 4 degrees C. There was no further change in these kinematic measurements after the cooled spermatozoa had undergone the second round of freeze-thawing. These results demonstrate that bull semen can be frozen and thawed, followed by a second freeze-thawing cycle of a population of spermatozoa selected by PureSperm, with retained motility and functional integrity. This points to the possibility of using double frozen spermatozoa in bovine artificial insemination programmes and to the potential benefits of PureSperm density gradient centrifugation for the application of cryopreserved bull spermatozoa to other biotechnological procedures such as flow cytometric sex sorting followed by re-freezing and thawing.

Assessment of the efficacy of Sephadex G-15 filtration of bovine spermatozoa for cryopreservation

Semen from five dairy AI bulls was split-filtered through a Sephadex G-15 filter and frozen in a Tris-citric acid buffer egg yolk-based extender. The effect of filtration was studied morphologically for individual sperm abnormalities. Computer-assisted sperm analysis (CASA) was used for motility and sperm motion assessment. Flow cytometry was used to disclose sperm viability (SYBR-14/PI), mitochondrial membrane potential (Mitotracker Deep Red/SYBR 14), acrosome integrity (SYBR 14/PE-PNA/PI), plasma membrane stability (Merocyanine 540/YO-PRO 1/Hoechst 333342), and chromatin stability (acridine orange staining). Filtration significantly reduced the concentration of recovered spermatozoa (P < 0.01), but improved semen quality, reducing the number of spermatozoa with various forms of morphological defects. Filtration also affected percentages of sperm motility after equilibration and after freezing/thawing. Sperm motion characteristics were, however, not significantly affected by filtration at any stage of the cryopreservation protocol, including post-extension, equilibration, or freezing/thawing. Filtration enhanced sperm viability after thawing (P < 0.05), but had no significant effect (P > 0.05) on recovery of spermatozoa with high mitochondrial potential, intact acrosomes, or preserved sperm chromatin structure. Sperm plasma membrane stability was also not affected by the filtration method used (P > 0.05). It can be concluded that filtration effectively separates weaken or abnormal spermatozoa in pre-freezing semen samples and therefore the procedure could be recommended to improve post-thaw sperm viability of selected, fertile sires.

Survival rate and antioxidant enzyme activity of ram spermatozoa after dilution with different extenders or selection by a dextran swim-up procedure

The aim of this study was to evaluate the effect of four extenders (Sucrose (S), Galactose (G), milk-yolk (MY), and Fiser (F)) on the motility, membrane integrity, and functional integrity of ram spermatozoa during liquid storage at 15 degrees C. The use of either S or MY for the selection of high quality spermatozoa by a swim-up procedure was comparatively analyzed. Additionally, the activity of three antioxidant enzymes, superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPx) was evaluated in both swim-up selected samples maintained at 15 degrees C for 6h. Sperm motility was better preserved in MY and was significantly higher after 6h of incubation than in either S or F (P<0.0001) and G (P<0.0005). Likewise, the incidence of spermatozoa with integral and functional membranes was higher in samples diluted in MY, with no significant decrease after 6h of incubation. The comparative analysis of the swim-up procedure performed with either MY or S revealed that not only was total sperm recovery significantly (P<0.001) higher (67.3%+/-3.21 versus 47.6%+/-3.78), but also that the best survival rate of spermatozoa was found in the MY stored sample. Sperm motility, viability and response to a hypoosmotic swelling (HOS) test were also significantly higher in the MY extended sample, maintaining still significantly higher values after 6h of incubation. In addition, this sample showed higher activity values for the antioxidant defense enzyme system.

Sperm evaluation in cryopreserved bovine semen recovered by two selection methods

Previous experiments have established that various semen manipulation techniques are able to increase the qualitative features of the spermatozoa used in different techniques of assisted reproduction, but practically no comparative data on frozen-thawed bovine semen have been found. The aim of this study was to compare the efficacy of two sperm selection methods: centrifugation on Percoll gradient and filtration through a Sephadex ion-exchange column, to improve the recovery of motile and morphologically normal spermatozoa, without inducing sperm damage, from cryopreserved bovine semen samples. Semen samples were thawed and centrifuged on a discontinuous Percoll gradient, or were filtered through a Sephadex G-15-120 column with the addition of ion exchangers. Sperm concentration, percentages of motile spermatozoa, acrosome integrity, superoxide dismutase activity and lipid peroxidation were evaluated in recovered samples and controls. The motility of spermatozoa obtained by Sephadex ion-exchange filtration (88.87 +/- 6.37%) and by Percoll gradient centrifugation (83.00 +/- 6.21%) were significantly greater than that of control samples (60.14 +/- 8.44%). Other results disclosed that both sperm selection methods significantly increased the percentage of intact acrosome and superoxide dismutase activity. In both cases, the number of recovered spermatozoa diminished significantly versus untreated samples. Although the number of recovered spermatozoa was low, these methods were effective to select viable sperm from cryopreserved bovine semen.

Sperm-lectin agglutination combined with swim-up leads to an efficient selection of highly motile, viable and heterogeneous ram spermatozoa

Lectins, high molecular weight glycoproteins with different sugar-binding specificity, are able to agglutinate different cell types. The recovery of high-quality spermatozoa can be facilitated by the agglutination induced by the lectin binding. The objective of this study was to combine sperm-lectin agglutination with a dextran/swim-up procedure for developing a new selection technique for ram spermatozoa. To study sperm quality, cell viability (plasma membrane integrity), the HOS-test response and progressive individual motility were assessed. Simultaneously, centrifugal countercurrent distribution (CCCD) in an aqueous two-phase system was carried out to analyze sperm surface heterogeneity. Semen from 3 mature Saltz rams was pooled, and 0.5-mL aliquots were incubated with 4 fluorescein-labelled lectins (ECL, JAC, PSA, RCA). Then, a dextran solution was gently added and overlaid with medium. The top layer of the medium containing the spermatozoa was collected and replaced by careful addition of fresh medium. The incubation sequence was repeated 3 times at 10-min intervals. The consecutive 4 top layers obtained were pooled to give the swim-up combined sample. The highest rate of improvement in sperm quality was obtained after incubation with RCA, with a 50% increase in progressive individual motility, 21.6% in HOS value and 39.5% in viability. Total cell recovery was 64% (1.56x10(9) cells), with a viable cell recovery rate of 86%. The obtained sample showed 82% motility, 80% HOS score and 77% viability, up from the pre-swim-up values of 51, 60 and 57 %, respectively. Comparative CCCD analysis revealed a very high heterogeneous population in the RCA/swim-up sample obtained, while a much more homogeneous population was obtained in the sample after the dextran/swim-up procedure previously developed byus With this simple method, a large proportion of highly-motile spermatozoa with preserved plasma membrane and high heterogeneity can be obtained. These results strongly suggest that this selection procedure could result in a high fertility rate.

Post-thaw plasma membrane integrity of bull spermatozoa separated with a sephadex ion-exchange column

Previous experiments have established that filtration of bovine semen through a Sephadex ion-exchange column improves its quality before and after freezing. The present study was conducted to determine the post-thaw membrane integrity of bull spermatozoa separated with a Sephadex ion-exchange column and to determine the kind of protection to spermatozoa is provided by glycerol during freezing and thawing. Semen from Holstein bulls diluted in TEST-yolk extender (with and without glycerol) was filtered through a Sephadex ion-exchange column and frozen in liquid nitrogen (-196 degrees C). After thawing, there were more normal acrosomes in filtered spermatozoa than nonfiltered (P < 0.01). Post-thaw plasma membrane integrity and swelling ability in a hypoosmotic solution revealed that the filtered spermatozoa had a stronger (P < 0.005) plasma membranes than the nonfiltered. Filtered spermatozoa demonstrated higher zona-free hamster oocyte penetration than the nonfiltered (30.5 vs 11.5%; P < 0.0005). Spermatozoa extended in TEST-yolk without glycerol had the lowest (P < 0.001) normal acrosomes, intact plasma membranes and swelling ability. Plasma membrane over the post-acrosomal region of the head and post-midpiece region of the tail was more sensitive to damages caused by freezing and thawing than acrosomal and midpiece regions of spermatozoa. Glycerol in the extender provided significant (P < 0.05) protection to the sensitive regions of filtered and nonfiltered spermatozoa during freezing and thawing. Filtered plus glycerolated spermatozoa had the highest (P < 0.01) normal acrosomes, intact plasma membranes and swelling ability. In conclusion, the pre-freezing filtration of bovine semen harvested the spermatozoa possessing stronger plasma membranes which enabled them to endure freezing and thawing stresses. The addition of glycerol to the extender protected the post-acrosomal region of the head and post-midpiece region of the tail of spermatozoa from freezing and thawing shocks.

Comparison of quality and freezability of water buffalo semen after washing or sephadex filtration

Split aliquots of pooled buffalo semen samples were processed before freezing 1) by washing twice with Tris-citric acid buffer by centrifugation and re-suspension to the original volume in the same buffer, or 2) or by passage through a G-15 Sephadex column. The effect of these procedures on progressive motility, percentages of live spermatozoa, sperm abnormalities and intact acrosomes and release of glutamate oxatoacetate transaminase (GOT) into the medium were assessed after extension, after equilibration and after 18 to 24 h or 15 d of frozen storage. Prior to extension, gel filtration reduced sperm concentration and enhanced progressive motility, whereas washing produced little effect on these attributes. Except in the case of GOT release, which was significantly (P < 0.05) lower after the washing of semen (34.3 +/- 16.40) than the filtering of semen (45.7 +/- 12.35), the 2 procedures did not cause significant effects (P > 0.05). Damage to spermatozoa due to freeze-processing was also similar in the 2 treatments, and the extent of beneficial effect in improved motility and live spermatozoan numbers after thawing was also similar.

Role of sperm motility and acrosome integrity in the filtration of bovine semen

In this study, the role of sperm motility and acrosome integrity in filtration of bovine semen was investigated. In Experiment 1, the treatment of semen with formaldehyde, hyperosmotic buffer, heating and direct freezing immobilized the spermatozoa completely but their acrosomal status varied significantly (P < 0.01). The immotile spermatozoa, of any kind, did not pass through the Sephadex ion-exchange column at room temperature. In Experiment 2, semen samples possessing different percentages of immobilized spermatozoa (0, 50, 75 and 100%) were filtered through the Sephadex ion-exchange column. The immotile/dead spermatozoa were removed proportionately to their number in the semen by Sephadex ion-exchange column. The type and number of immotile spermatozoa in semen had no effect (P > 0.05) on the post-filtration recovery rate of motile spermatozoa. Filtered spermatozoa exhibited higher (P < 0.01) motility (> 90%), progressive motility (> 70%) and normal acrosomes (> 95%) than non-filtered spermatozoa. In conclusion, sperm motility seems to be more important than acrosome integrity for semen filtration, and the Sephadex ion-exchange column can remove the known quantities of different kinds dead/immotile spermatozoa.

Morphology of nexin links in relation to interdoublet sliding in the sperm flagellum

In this work, we examine whether the "nexin" linkages of the flagellum can extend in length to accommodate interdoublet sliding. Flagellar bends of large angle were induced in bull spermatozoa by hypotonic treatment. It is argued that this produces large interdoublet displacements that are, nevertheless, still within physiological limits. Such flagella were examined by the rapid-freeze, deep-etch technique and the nexin linkages identified by their position in relation to the inner dynein arms and by their straplike, bipartite, morphology. They were found to bridge perpendicularly (or occasionally at an angle) between the A- and B-tubules of adjacent doublets. The nexin linkages were no more than approximately nm in length, even in regions in which approximately 200 nm of sliding could be inferred. Variable registration between adjacent nexin rows gave some further support to the assumption that sliding had indeed taken place. From this, it is concluded that elastic deformation of the links, such as would accommodate interdoublet sliding, does not occur; some form of displacement must occur between nexin and the adjacent B-tubule.

Advances in the cryopreservation of salmonid semen and suitability for a production-scale artificial fertilization program

During the past decade, semen cryopreservation techniques in salmonid fish have progressed to where fertilization rates obtained with preserved sperm approach those produced with fresh sperm. Recent advances in the collection, dilution and storage of salmonid spermatozoa are reviewed. The problems encountered during the development and examination of artificial insemination programs in warm-blooded animals are contrasted with those encountered in fish. This paper discusses the advantages of artificial fertilization, and the manner in which advances in cryopreservation techniques could aid in the development and expansion of concentrated, production-scale artificial fertilization programs in salmonid fish.

Effects of in vitro storage on the ATP-phosphohydrolase activity and ultrastructure of ejaculated bull sperm

Extended bull ejaculates were stored in vitro at 4 +/- 1 degree C in the dark. The pH of the ejaculates did not change significantly during storage. The percentage of sperm with intact plasmalemmae was 70% on day 2 and negligible by day 36. On day 2, acrosomes were absent in 3% of the sperm and partial in about 20%; acrosomal damage increased with storage, and by day 36 acrosomes were absent in 12% of the sperm and partially degraded in 72%. The Mg++-ATPase activity decreased from 2.6 to 1.9 microM Pi liberated per 2 X 10(7) sperm per 30 min incubation at 37 degrees between days 2 and 9, but remained at about 65% of its initial value between days 9 and 36. Thin-sectioned sperm sampled from ejaculates at days 2, 9, and 36 of storage showed a gradual but steady deterioration, which began and was most drastic in the head. Flagellar deterioration was negligible on day 9, but by day 36 subtle evidence of deterioration appeared. The persistence of Mg++-ATPase at 65% of initial levels in sperm stored 36 days in vitro is probably attributable to the stability of the movement-related flagellar ATPases.

The interaction of cAMP with modeled bull sperm

Demembranated and membrane disrupted bull sperm models exhibit an increase in motility when exposed to cAMP. Tritium-labeled cAMP was used to locate the initial site of action of cAMP in the modeled sperm preparations. cAMP did not bind selectively to the modeled cells, and the presence or absence of plasma membrane fragments on the models did not significantly alter this result. When suspension medium taken from modeled sperm preparations was subjected to gel filtration on Sephadex G25-150 columns, cAMP bound to a high molecular weight component that eluted with the void volume. The responsible binding factor is a soluble component that is released when the plasma membranes of the sperm are disrupted during the modeling procedure. To test the importance of the cAMP binding factor, modeled sperm were centrifuged, the supernatant solution was decanted, and the cells were resuspended in fresh medium. After this treatment the cells could be restored to motility with Mg-ATP but no longer exhibited a response to cAMP. Furthermore, addition of cAMP binding factor isolated by gel filtration partially restored the response of these sperm to cAMP. Investigation of the properties of the cAMP-binding factor have confirmed that it is specific for cAMP, with a much lower affinity for AMP and cGMP. In the presence of a large excess of unlabeled cAMP the labeled complex has a half-life of approximately 1 hour. Our results indicate that the action of cAMP on the motility of modeled sperm is mediated by its attachment to a high molecular weight, soluble component of the cell cytoplasm.