Cryopreservation of boar semen. I: A literature review

Crude Garden Cress Seed Oil (Lepidium sativum Linn.) Enhances Post-Thawed Boar Sperm Quality

This study aimed to examine the effects of crude garden cress seed oil (CGCSO) on frozen-thawed boar sperm qualities. Semen ejaculates (n = 12) were collected and further divided into six equal aliquots based on CGCSO concentrations (0, 0.5, 1, 1.5, 2, and 2.5% v/v) in the freezing extender. Semen samples were processed and cryopreserved utilizing the traditional liquid nitrogen vapor technique. Subsequently, semen samples were thawed in a thermos with warm water at 50 °C for 12 s and evaluated for sperm morphology using scanning electron microscopy, sperm motility using a CASA, sperm viability, acrosome integrity, mitochondrial function, MDA level, total antioxidant capacity (TAC), glutathione peroxidase (GSH-Px), and catalase (CAT) activity. The results indicated that 1% CGCSO resulted in superior post-thaw sperm characteristics, including enhanced sperm morphology, motility, viability, acrosome integrity, and mitochondrial function. Particularly, the total motile sperm increased by 16.5%, progressive motile sperm increased by 13.0%, viability improved by 15.1%, acrosome integrity increased by 14%, and mitochondrial function improved by 14.1% compared to the control group. CGCSO treatment at 1% and 1.5% exhibited the lowest level of MDA (45.73 ± 11.2 and 45.73 ± 11.3 µmol/L, respectively) compared to the other groups. The CGCSO-supplemented groups showed higher values of TAC, GSH-Px, and CAT than the control group but not significantly.

Carboxylated ε-Poly-L-Lysine Supplementation of the Freezing Extender Improves the Post-Thawing Boar Sperm Quality

Simple Summary

Frozen boar sperm is used on a very limited scale in pig artificial insemination owing to the low quality of post-thaw sperm. Cryoprotectant is usually used in boar sperm freezing extender, which is important for improving the post-thaw sperm quality. The carboxylated ε-poly-L-lysine, an efficient and non-toxic cryoprotectant, has been used as a food and cell preservative, as well as for tissue engineering and drug delivery in the biomedical applications. However, whether addition of carboxylated ε-poly-L-lysine to the freezing medium improves the post-thaw boar sperm quality or not is unknown. In this study, the addition of 0.25% carboxylated ε-poly-L-lysine to the freezing medium significantly improved the post-thaw boar sperm quality by protecting sperm mitochondrial function and antioxidant defense system.

Abstract

Frozen boar sperm is used on a minimal scale in consequence of the cryo-injuries induced by biochemical and physical modifications during the freezing and thawing processes. The present study investigates whether the addition of carboxylated ε-poly-L-lysine (CPLL) to the freezing medium could improve post-thaw boar sperm quality or not. Boar sperm was diluted with freezing medium contained different doses of carboxylated ε-poly-L-lysine (0, 0.125%, 0.25%, 0.5%, and 1%; v/v). The motility patterns, membrane integrity, acrosome integrity, mitochondrial membrane potential, NADH-CoQ activity, ATP level, malondialdehyde (MDA) level, and antioxidant defense system, as well as apoptosis in post-thaw boar sperm, were measured. It was observed that 0.25% CPLL treatment significantly improved the post-thaw boar sperm total motility, progressive motility, straight-linear velocity (VSL), curvilinear velocity (VCL), average path velocity (VAP), linearity (LIN), straightness (STR), membrane integrity, and acrosome integrity. Interestingly, the addition of CPLL also significantly increased the post-thaw sperm mitochondrial membrane potential, NADH-CoQ activity, and ATP level. Moreover, post-thaw boar sperm catalase (CAT) activity, glutathione peroxidase (GPx) activity, and superoxide dismutase (SOD) activity were increased with the addition of CPLL from 0.125% to 0.5% concentration levels. Furthermore, reduction of post-thaw sperm MDA level and apoptosis in 0.25% CPLL treatment was also observed. Those observations suggested that the addition of 0.25% CPLL to the freezing medium increased post-thaw boar sperm quality by protecting sperm mitochondrial function and antioxidant defense system. These findings provided novel insights that CPLL can be used as an efficient cryoprotectant to improve the post-thaw boar sperm quality during cryopreservation.

Role of Membrane Lipid Fatty Acids in Sperm Cryopreservation

Lipid is an important constituent of cell membrane. Membrane lipid composition of spermatozoa has been correlated to different function. Many researchers have related membrane lipid with survival success after cryopreservation or cold shock. Sperm maturation and acrosome reactions are natural phenomenon, but cryopreservation or cold shock is not. Therefore, sperm cells are not programmed for such change and undergo stress. So the change in membrane lipid composition due to cold shock or cryopreservation may be looked upon as response of spermatozoa to a certain stressed condition. A significant body of research worked on the relationship between membrane lipid and fatty acid composition and ability of cell to tolerate adverse change in temperature. However, as the approach of different research groups was different, it is very difficult to compare the changes. Studies have been done with different species, ejaculated/seminal or epididymal sperm. Lipid analyses have been done with whole cell membrane isolated by different methods. Fatty acids estimated were from whole cell, plasma membrane, head membrane, or phospholipids. The cryopreservation condition, media composition, and diluents/cryoprotectants were also different. At this onset a comprehensive review is needed to cover changes of sperm membrane lipid composition of different species under different cryopreservation conditions.

Boar semen can tolerate rapid cooling rates prior to freezing

Two experiments were performed in the present study that demonstrated that boar spermatozoa are capable of surviving rapid cooling rates within a range of 15–5°C before freezing. Boar ejaculates diluted in Beltsville thawing solution (BTS) (1 : 1, v/v) were held at 17–20°C and shipped over a 24-h time period from two AI centres to a cryobiology laboratory, where they were pooled (Experiment 1) or cryopreserved individually (Experiment 2) using a standard 0.5-mL straw freezing protocol. The effects of cooling before freezing were assessed after thawing through the objective evaluation of sperm motility and flow cytometric analysis of membrane integrity, acrosomal status, changes in membrane lipid architecture monitored by merocyanine and annexin V binding and intracellular production of reactive oxygen species. In Experiment 1 (six replicates), two semen pools (five ejaculates per pool) were cooled from 15 to 5°C at rates of 0.08, 0.13, 0.40 and 1.50°C min–1. These cooling rates did not result in any significant differences (P > 0.05) in any of the post-thaw sperm assessments, even in thawed samples incubated under capacitation conditions. In Experiment 2, three individual ejaculates from 16 boars were slowly (0.08°C min–1) or rapidly (1.5°C min–1) cooled before freezing. A consistent interboar variability (P < 0.01) was detected, which was independent of the cooling rate used. Cooling rate only significantly influenced (P < 0.05) sperm assessments in four of 16 boars, which exhibited slightly higher percentages of motile cells and intact plasma and acrosomal membranes in the samples that had been cooled slowly. These findings demonstrate that boar spermatozoa undergoing cryopreservation can withstand rapid cooling rates before freezing.

Advances in boar semen cryopreservation

The present paper highlights aspects of the cryopreservation of boar semen, a species with particular large, fractionated ejaculates, and a cumbersome cryotechnology that had prevented its commercial application. With the dramatic increase of use of liquid pig semen for artificial breeding over the past decade, developments on cryopreservation alongside the routine use of stud boar semen for AI had been promoted. Recent advances in our laboratory, accommodating the best use of portions of the sperm-rich fraction of the ejaculate for cryopreservation of the sperm-peak portion (P1) and parallel use of the rest of the collected ejaculated spermatozoa, appears as a suitable commercial alternative.

Preservation and transplantation of porcine testis tissue

Grafting of immature mammalian testis tissue to mouse hosts can preserve the male germline. To make this approach applicable to a clinical or field situation, it is imperative that the testis tissue and/or spermatozoa harvested from grafted tissue are preserved successfully. The aim of the present study was to evaluate protocols for the preservation of testis tissue in a porcine model. Testis tissue was stored at 4 degrees C for short-term preservation or cryopreserved by slow-freezing, automated slow-freezing or vitrification for long-term storage. Preserved tissue was transplanted ectopically to mouse hosts and recovered xenografts were analysed histologically. In addition, spermatozoa were harvested from xenografts and cryopreserved. Total cell viability and germ cell viability remained high after tissue preservation. Complete spermatogenesis occurred in xenografts preserved by cooling up to 48 h, whereas spermatogenesis progressed to round spermatids in the xenografts that were frozen-thawed before grafting. Approximately 50% of spermatozoa harvested from xenografts remained viable after freezing and thawing. The in vivo developmental potential of cryopreserved tissue was reduced despite high post-thaw viability. Therefore, it is important to evaluate germ cell differentiation in vivo in addition to cell viability in vitro when optimising freezing protocols for testis tissue.

Effects of cryopreservation on semen quality and the expression of sperm membrane hexose transporters in the spermatozoa of Iberian pigs

This study evaluated the effects of cooling, freezing and thawing on the plasma membrane integrity, kinetics and expression of two sugar transporters glucose transporter-3 and -5 (GLUT-3 and GLUT-5) in spermatozoa from Iberian boars. Semen samples were collected twice weekly from eight young, fertile Iberian boars of the 'Entrepelado' and 'Lampiño' breeds. The samples were suspended in a commercial extender and refrigerated to 17 degrees C for transport to the laboratory (step A), where they were further extended with a lactose-egg yolk-based extender and chilled to 5 degrees C (step B) prior to freezing in the presence of glycerol (3%). Spermatozoa were assessed for plasma membrane integrity and sperm motility at each of the steps, including post-thaw (step C). Aliquots were also prepared for immunocytochemical localisation of the sugar transporters (fixed and thin smears for transmission and scanning electron microscopy levels respectively) and for SDS-PAGE electrophoresis and subsequent western blotting, using the same antibodies (rabbit anti-GLUT-3 and anti-GLUT-5 polyclonal antibodies). The results showed lower percentages of progressively motile spermatozoa at step C in both breeds, while the percentage of live spermatozoa was significantly lower only in the 'Entrepelado' breed. The results obtained from electron microscopy clearly showed that Iberian boar spermatozoa expressed the hexose transporters, GLUT-3 and GLUT-5. The pattern of expression, in terms of location and concentration, was characteristic in each case but, in the case of isoform GLUT-5, it remained constant during the different steps of freezing-thawing protocol. These results indicate that cryopreservation affects the status of sperm cells of Iberian boars by altering the distribution of some membrane receptors and decreasing the percentage values of parameters linked to sperm quality.

The effect of osmotic stress on the cell volume, metaphase II spindle and developmental potential of in vitro matured porcine oocytes

Porcine animal models are used to advance our understanding of human physiology. Current research is also directed at methods to produce transgenic pigs. Cryobanking gametes and embryos can facilitate the preservation of valuable genotypes, yet cryopreserving oocytes from pigs has proven very challenging. The current study was designed to understand the effects of anisotonic solutions on in vitro matured porcine oocytes as a first step toward designing improved cryopreservation procedures. We hypothesized that the proportion of oocytes demonstrating a normal spindle apparatus and in vitro developmental potential would be proportional to the solution osmolality. Oocytes were incubated for 10 min at 38 degrees C in various hypo- or hypertonic solutions, and an isotonic control solution and then assessed for these two parameters. Our results support the hypothesis, with an increasing proportion of spindles showing a disrupted structure as the levels of anisotonic exposure diverge from isotonic. Only about half of the oocytes maintained developmental potential after exposure to anisotonic solutions compared to untreated controls. Oocyte volume displayed a linear response to anisotonic solutions as expected, with an estimated relative osmotically inactive cell volume of 0.178. The results from this study provide initial biophysical data to characterize porcine oocytes. The results from future experiments designed to determine the membrane permeability to various cryoprotectants will allow predictive modeling of optimal cryopreservation parameters and provide a basis for designing improved cryopreservation procedures.

The influence of trehalose, taurine, cysteamine and hyaluronan on ram semen

There is a lack of information regarding lipid peroxidation and antioxidant capacity in cryopreserved ram semen, and cryopreservation is associated with the production of reactive oxygen species (ROS) which lead to lipid peroxidation (LPO) of sperm membranes, resulting in a loss of motility, viability and fertility of sperm. The aim of this study was to determine the influence of certain additives and their different doses on standard semen parameters, lipid peroxidation and antioxidant activities after the cryopreservation/thawing of ram semen. Ejaculates collected from four Akkaraman rams, a native breed of sheep, were evaluated and pooled at 33 degrees C. Semen samples which were diluted with a Tris-based extender containing additives including trehalose (50, 100mM), taurine (25, 50mM), cysteamine (5, 10mM), and hyaluronan (0.5, 1mg/ml), and an extender containing no additives (control) were cooled to 5 degrees C and frozen in 0.25ml French straws, being stored in liquid nitrogen. Frozen straws were thawed individually at 37 degrees C for 20s in a water bath for evaluation. The use of a Tris-based extender supplemented with 50mM trehalose, 25mM taurine, and 5 and 10mM cysteamine led to higher percentages of post-thaw motility, in comparison to the control group (P<0.01). No significant differences were observed in the percentages of acrosome and total abnormalities, and the hypoosmotic swelling test upon the supplementation of the freezing extender with antioxidants after the thawing of semen. In biochemical assays, the addition of antioxidants did not cause significant differences in levels of malondialdehyde (MDA), glutathione (GSH), and glutathione peroxidase (GSH-Px), after thawing, when compared to groups with no additives. In this study, catalase (CAT) activities were higher in the group that was applied 25mM taurine as an antioxidant, than in all of the other groups (P<0.001). Compared to the controls, antioxidant treatment with 100mM trehalose, 50mM taurine, 5mM cysteamine and 0.5mg/ml hyaluronan, significantly elevated vitamin E (vit E) levels in samples (P<0.001).

Effects of exposure of pre-pubertal boars to di(2-ethylhexyl) phthalate on their frozen-thawed sperm viability post-puberty

Late effects of pre-pubertal oral exposure to di(2-ethylhexyl) phthalate (DEHP), a plastic softener used in, for example, polyvinyl chloride-products, on semen quality in young boars have not been clear-cut. The aim of this study was to determine whether stress imposed on spermatozoa would reveal such effects. Semen was collected from post-pubertal boars (8-9 months of age), which had been exposed to 300 mg kg(-1) body weight of DEHP per os three times a week from 3 to 7 weeks of age and from control siblings given placebo (water). The semen was cryopreserved and examined for plasma membrane integrity post-thaw using the short hypo-osmotic swelling test and flow cytometry (propidium iodide /SYBR-14). Sperm motility was assessed by computer-assisted sperm analysis. No significant difference in plasma membrane integrity could be found between the groups. The DEHP-exposed group had a significantly lower percentage of linearly motile spermatozoa at 30 min (P < 0.05) and 120 min (P < 0.001) after thawing, and a larger amplitude of lateral displacement of the head 120 min after thawing (P < 0.05), compared with controls. In summary, spermatozoa from boars pre-pubertally exposed to low doses of DEHP, showed kinematic deviations post-thaw that could be related to DEHP exposure.

Effect of different thawing temperatures on the viability, in vitro fertilizing capacity and chromatin condensation of frozen boar semen packaged in 5 ml straws

The effect of two different thawing temperatures on frozen boar semen viability, in vitro fertilizing capacity and chromatin condensation and stability was studied. Freeze-thaw motility, normal apical ridge (NAR), in vitro fertilizing (IVF) capacity and chromatin condensation and stability were evaluated after thawing at 42 degrees C, 40s and 50 degrees C, 40s. Chromatin condensation degree was determined by flow cytometry, using propidium iodide as fluorochrome intercalating agent, and chromatin stability was evaluated by the same procedure after inducing sperm chromatin decondensation with ethylene diamine tetraacetic acid (EDTA) and sodium dodecyl sulfate (SDS). The results showed that thawing straws at 42 degrees C, 40s significantly reduced motility compared to straws thawed at 50 degrees C, 40s. NAR, penetration, monospermy and polyspermy were not different between the two groups of samples thawed at different temperatures. Chromatin was significantly more compact when thawing was performed at 50 degrees C, but its stability did not show any difference relative to thawing at 42 degrees C. It is suggested that the interactions involved in chromatin overcondensation had a non-covalent nature.

Deep freezing of concentrated boar semen for intra-uterine insemination: effects on sperm viability

The use of deep-frozen boar semen for artificial insemination (AI) is constrained by the need for high sperm numbers per dose, yielding few doses per ejaculate. With the advancement of new, intra-uterine insemination strategies, there is an opportunity for freezing small volumes containing high sperm numbers, provided the spermatozoa properly sustain cryopreservation. The present study aimed to concentrate (2 x 10(9) spz/mL) and freeze boar spermatozoa packed in a 0.5 mL volume plastic medium straw (MS) or a multiple FlatPack (MFP) (four 0.7 mL volume segments of a single FlatPack [SFP]) intended as AI doses for intra-uterine AI. A single freezing protocol was used, with a conventional FlatPack (SFP, 5 x 10(9) spz/5 mL volume) as control. Sperm viability post-thaw was monitored as sperm motility (measured by computer-assisted sperm analysis, CASA), as plasma membrane integrity (PMI, assessed either by SYBR-14/PI, combined with flow cytometry, or a rapid hypo-osmotic swelling test [sHOST]). Sperm motility did not differ statistically (NS) between test-packages and control, neither in terms of overall sperm motility (range of means: 37-46%) nor sperm velocity. The percentages of linearly motile spermatozoa were, however, significantly higher in controls (SFP) than in the test packages. Spermatozoa frozen in the SFP (control) and MFP depicted the highest PMI (54 and 49%, respectively) compared to MS (38%, P < 0.05) when assessed with flow cytometry. In absolute numbers, more viable spermatozoa post-thaw were present in the MFP dose than in the MS (P < 0.05). Inter-boar variation was present, albeit only significant for MS (sperm motility) and SFP (PMI). In conclusion, the results indicate that boar spermatozoa can be successfully frozen when concentrated in a small volume.

Changes in sperm quality and lipid composition during cryopreservation of boar semen

Egg yolks are commonly used in diluents in order to improve the freezability of semen. Two aspects of the role of lipids in boar semen freezability are reported in this article. The first one concerns the eventual exchanges of lipid components between the spermatozoa and the yolk-based diluent during cryopreservation. Two types of yolk have been considered as ingredients in diluents for cryopreservation: yolks with a standard fatty acid composition and yolks enriched in docosahexaenoic acid (DHA). The relation between lipid exchanges and the quality of fresh semen is considered. The other aspect concerns the possibility to enhance the freezability of boar spermatozoa by altering the plasma membranes under the influence of dietary fatty acids. Spermatozoa were damaged significantly by the cryopreservation cycle in all experiments. Spermatozoa with the best fresh quality had accumulated the largest quantity of lipids upon thawing. A general decrease in the proportion of polyunsaturated fatty acids was observed after thawing. The yolks enriched in n-3 fatty acids failed to improve the quality of sperm following cryopreservation. The proportion of DHA was significantly higher in spermatozoan phospholipids from thawed cells that had been in contact with n-3 yolks. A significant reduction in cholesterol was observed in spermatozoa after the cryopreservation cycle, which correlated with an increased number of acrosome-reacted cells and changes in the parameters of motility. The addition of 3% fish oil to the daily boar ration significantly increased the content of DHA (from 33 to 45% of the total fatty acids) in the spermatozoa. Ejaculate concentrations were significantly increased in the experimental group. DHA-enriched semen did not show improved freezability, at least not as assessed by in vitro parameters.

Subzero water transport characteristics of boar spermatozoa confirm observed optimal cooling rates

Incomplete understanding of the water transport parameters (reference membrane permeability, L(pg), and activation energy, E(Lp)) during freezing in the presence of extracellular ice and cryoprotective agents (CPAs) is one of the main limiting factors in reconciling the difference between the numerically predicted value and the experimentally determined optimal rates of freezing in boar (and in general mammalian) gametes. In the present study, a shape-independent differential scanning calorimeter (DSC) technique was used to measure the water transport during freezing of boar spermatozoa. Water transport data during freezing of boar sperm cell suspensions were obtained at cooling rates of 5 and 20 degrees C/min in the presence of extracellular ice and 6% (v/v) glycerol. Using previously published values, the boar sperm cell was modeled as a cylinder of length 80.1 microm and a radius of 0.31 microm with an osmotically inactive cell volume, V(b), of 0.6 V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained data, the best-fit water transport parameters (L(pg) and E(Lp)) were determined. The "combined-best-fit" parameters at 5 and 20 degrees C/min for boar spermatozoa in the presence of extracellular ice are: L(pg) = 3.6 x 10(-15) m(3)/N. s (0.02 microm/min-atm) and E(Lp) = 122.5 kJ/mole (29.3 kcal/mole) (R(2) = 0.99); and the corresponding parameters in the presence of extracellular ice and glycerol are: L(pg)[cpa] = 0.90 x 10(-15) m(3)/N. s (0.005 microm/min-atm) and E(Lp)[cpa] = 75.7 kJ/mole (18.1 kcal/mole) (R(2) = 0.99). The water transport parameters obtained in the present study are significantly different from previously published parameters for boar and other mammalian spermatozoa obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The theoretically predicted optimal rates of freezing using the new parameters ( approximately 30 degrees C/min) are in close agreement with previously published but experimentally determined optimal cooling rates. This analysis reconciles a long-standing difference between theoretically predicted and experimentally determined optimal cooling rates for boar spermatozoa.

Analysis of in vitro fertilizing capacity to evaluate the freezing procedures of boar semen and to predict the subsequent fertility

A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen-thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37 degrees C, 30 s; 50 degrees C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50 degrees C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility > or = 80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen-thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability.

Assessment of suitable porcine semen for freezing, according to the ejaculate characteristics in the Iberico x Landrace breed

A total of 35 ejaculates were studied in order to assess the suitability of porcine semen for freezing according to the ejaculate characteristics. The effects of the freezing procedure were identified; a decrease in motility and acrosome quality was found after thawing. The best results on motility were linked to the ejaculates with a volume of less than 100 ml of the sperm-rich fraction, a concentration lower than 450 x 10(6) spermatozoa/ml and an agglutination score below 2. However, the best normal apical ridge (NAR) was found when the volume of the sperm-rich fraction was greater than 150 ml. For this reason, an intermediate volume of the sperm-rich fraction of the ejaculate for the best motility and the best NAR, a concentration lower than 450 x 106 spermatozoa/ml and a rate of agglutination below 2 should provide the best quality after freezing. This study also attempted to determine whether a positive effect of ejaculate selection on the overall freezing performance might be expected.

Effect of preincubation of cryopreserved porcine epididymal sperm

Preincubation of spermatozoa is important for capacitation and successful fertilization in vitro. The effects of preincubation time on frozen-thawed boar epididymal spermatozoa as measured by sperm motility, acrosomal integrity and fertilization ability in vitro were examined. Epididymal spermatozoa were collected from three Large White boars and frozen. The thawed spermatozoa were preincubated for 0, 15, 30, 60 and 120 min. Their motility was evaluated by a sperm motility analyzer and then the sperm motility indexes (SMIs) were calculated. The status of their acrosomal integrity was evaluated by triple-staining. Then, their fertilization ability was examined by in vitro fertilization (IVF) using porcine oocytes matured in vitro. SMIs of spermatozoa and the incidences of acrosome-intact live spermatozoa from the three boars were high (21-39 for SMI and 50-61% for acrosome-intact live spermatozoa) just after thawing, but both decreased as the duration of preincubation was prolonged (2-10 and 23-40%, respectively). The incidences of sperm penetration were high (61-89% of inseminated oocytes) when the sperm were preincubated for 0-60 min. However, sperm penetration decreased as the preincubation period was prolonged to 120 min. The degree of this decrease differed depending upon the boar from which the spermatozoa were obtained (10-72%). When the two parameters, sperm motility and acrosomal integrity, were analyzed statistically, the latter parameter rather than the former one showed a significant effect on penetration ability in vitro after each duration of preincubation. These results suggest that preincubation of frozen-thawed boar epididymal spermatozoa is not required for IVF and also that the maintenance of acrosomal integrity in unreacted status, rather than the maintenance of sperm motility, is important for fertilization ability after thawing and during preincubation of boar epididymal spermatozoa.

Incorporating lipids into boar sperm decreases chilling sensitivity but not capacitation potential

Fresh boar sperm were incubated with small unilamellar liposomes composed of either the total lipids extracted from head plasma membranes (HPM) of fresh boar sperm or selected lipids (SL) of five defined phospholipids with specific acyl chains. To optimize fusion, liposomes with 2 mol% octadecyl rhodamine fluorophore in Beltsville Thawing Solution +/- 1 mM CaCl(2) were incubated at 35 degrees C with 1;ts 10(7) or 10(8) spermatozoa/ml and monitored over 60 min, using flow cytometry and fluorescence microscopy. The HPM fused to both sperm concentrations faster than SL but was equivalent by 30 min (10(8) sperm/ml) or 60 min (10(7) sperm/ml; 57.5 +/- 3% and 67.1 +/- 8% sperm fused to HPM and SL, respectively) +/- Ca(2+). Neither HPM nor SL affected onset of capacitation or spontaneous or ionophore-induced acrosome reactions at 0 or 3 h (chlortetracycline and fluorescein isothiocyanate-Pisum sativum agglutinin; n = 3). During cooling and after cryopreservation (n = 4 ejaculates), SL but not HPM significantly improved sperm motility and viability (Sybr14/propidium iodide staining) +/- 20% egg yolk, but egg yolk alone was more effective than SL alone. Liposomes of complex composition can fuse to boar sperm without harming in vitro capacitation or acrosome reaction and reduce sperm chilling sensitivity.

Basic aspects of frozen storage of semen

Basic concepts of cryopreservation and the causes of cryoinjury are reviewed. The possible roles of cryoprotectants and additives are considered in the context of their putative interactions with the sperm plasma membrane. Modern approaches to the laboratory assessment of spermatozoa after freeze-thawing are also briefly discussed.

Storage of boar semen

The problems, aspects and methods of liquid storage and freeze-thawing of boar semen are discussed and a review is given on examination of spermatozoa by the recent fluorescent staining methods.

Deep-freezing of boar semen in plastic film 'cochettes'

The motility and membrane integrity of spermatozoa from nine boars frozen with a programmable freezing machine in plastic bags, 'cochettes', and in 'maxi-straws', in total doses of 5 x 10(9) spermatozoa/5 ml with glycerol (3%) used as cryoprotectant, were assessed after thawing. A computer-based cell motion analyser was used to evaluate sperm motility, while the integrity of the plasmalemma was assessed with fluorescent supravital dyes (C-FDA/PI). The fertilizing capacity of the semen frozen in the two containers was investigated by inseminating (AI) gilts. Pregnancy was monitored by Doppler-ultrasound, and the numbers of corpora lutea and viable embryos counted at slaughter, between days 30 and 38 after AI. The cochettes sustained the overall procedure of freezing/thawing (FT), with 30 min post-thaw (PT) sperm motility being significantly higher than for straws, 46.9 vs. 39.5%. The only significant difference in motility patterns detected when comparing the packages was a higher sperm velocity (VCL) in cochettes at 30 min PT. However, percentages of FT-spermatozoa with intact membranes, detected with the supravital probes, were higher in maxi-straws than in cochettes, 46.8 vs. 43.0% (P < 0.05). There were no significant differences found in fertilizing capacity between spermatozoa frozen in maxi-straws and those frozen in cochettes. The results indicate that although the deep-freezing of AI-doses of boar semen in large plastic bags is feasible, problems such as their inconvenient size for storage and inconsistent thawing must be solved before this type of container can be used for the commercial cryopreservation of boar semen.

Cryopreservation of mouse spermatozoa. I. Effect of seeding on fertilizing ability of cryopreserved spermatozoa

To examine the effect of seeding to induce ice formation during cryopreservation on their survival, spermatozoa from B6D2F1 mice were cooled to and held at -4 degrees C for 30 min in phosphate-buffered saline (PBS) alone, in egg yolk-supplemented PBS, or in PBS with raffinose + glycerol as cryoprotective additives (CPAs). Seeding and holding spermatozoa at -4 degrees C did not affect their viability as judged by vital staining. Egg yolk protected spermatozoa against chilling injury, as cooling them to -4 degrees C in the presence of egg yolk yielded higher survivals than those cooled without egg yolk (34.4 +/- 3.4 v 9.0 +/- 1.3% in three replicates of >400 spermatozoa/replicate). To study effects of seeding on their fertilizing ability, spermatozoa in the raffinose-glycerol-egg yolk solution were frozen to -196 degrees C either without seeding or after seeding at -4 degrees C. Development of 222 oocytes into two-cell embryos after in vitro fertilization (IVF) with spermatozoa frozen without seeding was 43%; development rates of 186, 186, and 207 oocytes after IVF with spermatozoa frozen after seeding and being held at -4 degrees C for 5, 10, or 30 min were 46, 44, and 9%, respectively. In a direct comparison, after IVF with seeded or unseeded spermatozoa the respective cleavage rates into two-cell embryos were 83% of 275 oocytes and 69% of 304 oocytes, a difference that was small but significant by chi2 analysis. An additional 925 oocytes were fertilized with spermatozoa after being seeded and frozen to -196 degrees C in four separate batches of CPA solutions. Overall, after IVF with frozen sperm, 68% of those oocytes cleaved into two-cell embryos and 59% developed into 544 blastocysts. Based on these results, we concluded that embryo production by IVF seemed to be improved using spermatozoa frozen after being seeded. Mouse spermatozoa cryopreserved by the method described here are capable of fertilizing oocytes at a rather high rate.

Membrane damage during dilution, cooling and freezing-thawing of boar spermatozoa packaged in plastic bags

The objective of the present investigation was to determine the degree of membrane damage in boar spermatozoa during the course of a cryopreservation procedure, including thawing. Ejaculates from four fertile Swedish Yorkshire boars were frozen under controlled conditions in Teflon-plastic bags (2.5 ml) using 3% glycerol as cryoprotectant. Membrane integrity was monitored using supravital fluorescent dyes and confirmed by scanning electron microscopy. The results show that cooling to +5 degrees C significantly affected the permeability of the plasmalemma. Supercooling (-6 degrees C) during the freezing program did not further deteriorate the integrity of the spermatozoal membrane. The thawing procedure however, dramatically increased the frequency of spermatozoa with damaged plasma membranes. Thus particular attention must be paid on designing a better thawing procedure when dealing with boar semen frozen in plastic bags.

Cryopreservation of boar semen. III: Ultrastructure of boar spermatozoa frozen ultra-rapidly at various stages of conventional freezing and thawing

Ejaculated boar spermatozoa subjected to a conventional freezing and thawing process, were ultra-rapidly fixed, freeze-substituted and examined by electron microscopy to monitor the presence of real or potential intracellular ice and the degree of cell protection attained with the different extenders used during the process. Numerous ice crystal marks representing the degree of hydration of the cells were located in the perinuclear space of those spermatozoa not in proper contact with the extender containing glycerol (i.e. prior to freezing). The spermatozoa which were in proper contact with the extenders presented a high degree of preservation of the acrosomes, plasma membranes as well as the nuclear envelopes. No ice marks were detected in acrosomes before thawing, indicating that the conventional assayed cryopreservation method provided a good protection against cryoinjury. The presence of acrosomal changes (internal vesiculization, hydration and swelling) in thawed samples however, raises serious questions about the thawing procedure employed.

Cryopreservation of boar semen. III: Ultrastructure of boar spermatozoa frozen ultra-rapidly at various stages of conventional freezing and thawing

Ejaculated boar spermatozoa subjected to a conventional freezing and thawing process, were ultra-rapidly fixed, freeze-substituted and examined by electron microscopy to monitor the presence of real or potential intracellular ice and the degree of cell protection attained with the different extenders used during the process. Numerous ice crystal marks representing the degree of hydration of the cells were located in the perinuclear space of those spermatozoa not in proper contact with the extender containing glycerol (i.e. prior to freezing). The spermatozoa which were in proper contact with the extenders presented a high degree of preservation of the acrosomes, plasma membranes as well as the nuclear envelopes. No ice marks were detected in acrosomes before thawing, indicating that the conventional assayed cryopreservation method provided a good protection against cryoinjury. The presence of acrosomal changes (internal vesiculization, hydration and swelling) in thawed samples however, raises serious questions about the thawing procedure employed.