Directional Freezing of Equine Semen in Large Volumes

An Investigation of Equine Sperm Quality Following Cryopreservation at Low Sperm Concentration and Repeated Freeze-Thawing

Stallion spermatozoa are typically cryopreserved at 200 to 300 million sperm/ml; however recent advances such as intracytoplasmic sperm injection (ICSI) requires only one spermatozoon, wasting many, after thawing a whole straw. Cryopreserving at concentrations less than the current standard or refreezing thawed spermatozoa could maximize the use of genetically valuable animals and reduce waste. This investigation aimed to identify if lowering the sperm concentration for cryopreservation affected post-thaw quality after one and two freeze-thaw cycles. Nine ejaculates were collected from three fertile, "good freezer" stallions (post-thaw motility ≥35%) for experiment 1. Each ejaculate was split into eight treatments: five, 10, 20, 50, 100, 200, 300, 400 million sperm/ml and cryopreserved. Post-thaw: motility, viability, acrosome integrity and oxidative stress were assessed. Experiment 2, straws from experiment 1 (300 million sperm/ml) were thawed, diluted to 20 million sperm/ml or left undiluted (control) and refrozen. Post-thaw motility and viability were assessed. In experiment 1 sperm concentration did not affect post-thaw total motility (TM), progressive motility (PM) or viability at 50 to 400 million sperm/ml (P > .05). Whilst sperm concentrations of five to 20 million/ml did differ (post-thaw TM and PM). Both refreezing and reducing spermatozoa concentration, decreased TM, PM and viability (P < .05) after two freeze-thaw cycles. These results suggest cryopreserving at sperm concentrations as low as 50 million/ml maintains spermatozoa quality in good freezer stallions. Spermatozoa maintained some motility and viability when initially cryopreserved at 20 million sperm/ml and after two freeze-thaw cycles but research should investigate more optimal conditions.

Cryo-scanning electron microscopy demonstrates that ice morphology is not associated with the post-thaw survival of domestic boar (Sus domesticus) spermatozoa: A comparison of directional and conventional freezing methods

Directional freezing (in 2 or 10 ml hollow glass tubes) has been reported to improve post-thaw sperm survival parameters compared to conventional methods (in 0.5 ml straws). However, the biophysical properties that increase post-thaw survival are poorly understood. Therefore, the aim for the current study was to investigate the effect of ice morphology on the post-thaw survival of domestic boar spermatozoa directionally and conventionally cryopreserved in 0.5 ml straws. Ice morphology was quantitatively analyzed using a combination of cryo-scanning electron microscopy and Fiji Shape Descriptors. Multivariate analysis found a significant, non-linear effect (p < 0.05) of interface velocity on ice morphology, with an increase in both ice-lake size, as indicated by area and in aspect ratio, at an interface velocity of 0.2 mm/s. By contrast, post-thaw sperm survival (defined as spermatozoa with both intact plasma membranes and acrosomes) was biphasic, with peaks of survival at interface velocities of 0.2 mm/s (54.2 ± 1.9%), and 1.0 or 1.5 mm/s (56.5 ± 1.5%, 56.7 ± 1.7% respectively), and lowest survival at 0.5 (52.1 ± 1.6%) and 3.0 mm/s (51.4 ± 1.9%). Despite numerical differences in Shape Descriptors, there was no difference (p > 0.05) in the post-thaw survival between conventionally and directionally cryopreserved samples at optimal interface velocities of 1.0 or 1.5 mm/s. These findings suggest that: 1) ice morphology has little impact on post-thaw survival of boar spermatozoa, and 2) directional freezing in 0.5 ml straws (rather than 2 or 10 ml hollow glass tubes) may attenuate benefits of directional freezing.

Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

Biodiversity is defined as the presence of a variety of living organisms on the Earth that is essential for human survival. However, anthropogenic activities are causing the sixth mass extinction, threatening even our own species. For many animals, dwindling numbers are becoming fragmented populations with low genetic diversity, threatening long-term species viability. With extinction rates 1000–10,000 times greater than natural, ex situ and in situ conservation programmes need additional support to save species. The indefinite storage of cryopreserved (−196°C) viable cells and tissues (cryobanking), followed by assisted or advanced assisted reproductive technology (ART: utilisation of oocytes and spermatozoa to generate offspring; aART: utilisation of somatic cell genetic material to generate offspring), may be the only hope for species’ long-term survival. As such, cryobanking should be considered a necessity for all future conservation strategies. Following cryopreservation, ART/aART can be used to reinstate lost genetics back into a population, resurrecting biodiversity. However, for this to be successful, species-specific protocol optimisation and increased knowledge of basic biology for many taxa are required. Current ART/aART is primarily focused on mammalian taxa; however, this needs to be extended to all, including to some of the most endangered species: amphibians. Gamete, reproductive tissue and somatic cell cryobanking can fill the gap between losing genetic diversity today and future technological developments. This review explores species prioritisation for cryobanking and the successes and challenges of cryopreservation and multiple ARTs/aARTs. We here discuss the value of cryobanking before more species are lost and the potential of advanced reproductive technologies not only to halt but also to reverse biodiversity loss.

Strategies to Minimize Various Stress-Related Freeze-Thaw Damages During Conventional Cryopreservation of Mammalian Spermatozoa

The aim of the article is to report a review on different sperm cryopreservation techniques, various stress-related freeze-thaw damages altering sperm structure and function during conventional cryopreservation, and strategies to minimize these stresses. Sperm cryopreservation has allowed indefinite storage and successful transportation of valuable germplasm from proven sites at distant locations, for genetic upgradation through implementation of reproductive techniques, such as artificial insemination. Different techniques for sperm cryopreservation have been proposed such as conventional freezing techniques, directional freezing, and sperm vitrification. Drawbacks related to conventional freezing methods, such as heterogeneous ice nucleation and repeated freeze-thaw cycles at the ice front that disrupts and kill sperm cells, led to the emergence of the directional freezing technique. Sperm vitrification is advantageous as there is no ice crystal-induced physical damages to sperm. However, sperm vitrification has less applicability as encouraging results are only reported in human, dog, and cat. In spite of several drawbacks, conventional freezing techniques are still most widely used for sperm cryopreservation. Spermatozoa experience stresses in the form of cold shock, osmotic stress, and mainly oxidative stress during conventional cryopreservation ultimately reduces the sperm viability and fertility. Several attempts have been made in the past to minimize all these stresses individually or in combination. Membrane fluidity was increased to prevent the cold shock and cryocapacitation-like changes by the addition of cholesterol to the membrane. Antifreeze proteins were added in semen extender to minimize freeze-thaw damages due to heterogeneous ice nucleation and ice recrystallization. Oxidative stress was reduced either by neutralizing reactive oxygen species (ROS) through enzymatic, nonenzymatic, plant-based antioxidants or reductants; or by minimizing the level of sources like the semen radiation exposure, leucocytes, and dead and defective spermatozoa, which lead to ROS production during the semen cryopreservation process. A novel approach of minimizing oxidative stress was to reduce the oxygen tension in sperm microenvironment that is, extender by partial deoxygenation process, as a number of literatures pointed out direct link of O₂ with ROS production. When compared with other strategies, partial deoxygenation of semen extender with N₂ gassing is found as a cost-effective, comparatively easy and a potential approach to large-scale frozen semen production.

Improvement in Semen Conservation of the Indigenous Czech Endangered Old Kladruber Horse: Special Focus on the Type of Extender and Packaging System

The aim of our study was to investigate the effect of two freezing extenders and two packaging systems on motility, plasma membrane (PM) integrity, and the apoptotic status of frozen-thawed (F-T) spermatozoa of the endangered Old Kladruber stallions. The collected semen (n = 6 stallions, three collections each) was diluted either with Gent or Lactose-EDTA (Lact) extender. Two aliquots of semen from each collection diluted in this way were prepared and then loaded into 5-mL aluminum tubes or 0.5-mL plastic straws. After thawing and then at 15 minutes intervals within 1 hour, the samples were analyzed for motility (CASA), PM integrity (CFDA/PI), and apoptotic changes of the spermatozoa (Yo-Pro-1/PI). Using Gent, the samples exhibited higher motility, kinematic parameters, higher representation of spermatozoa in medium, and fast subpopulation, as well as more spermatozoa with intact PMs and fewer spermatozoa with apoptotic changes compared with Lact extender (P < .05). Progressive motility and PM integrity was superior when using Gent and 5-mL aluminum tubes as compared with the rest of the combinations (P < .05). Kinematic parameters, percentage of spermatozoa in fast subpopulation and apoptotic status was superior in Gent and 0.5-mL straws as compared with the rest of the combinations (P < .05). Moreover, we revealed that F-T semen reacts diametrically differently when two different extenders and packaging systems are used. The study concludes that the combination of Gent and 0.5-mL straws represent adequate freezing system to maintain the appropriate quality of spermatozoa of this endangered breed.

Freezing, Vitrification, and Freeze-Drying of Equine Spermatozoa: Impact on Mitochondrial Membrane Potential, Lipid Peroxidation, and DNA Integrity

Maintaining the integrity of equine sperm subjected to preservation protocols is essential for the successful development of assisted reproduction procedures. The aim of this study was to assess the mitochondrial membrane potential, lipid peroxidation, and DNA integrity of equine sperm subjected to freezing, vitrification, and freeze-drying. Eight ejaculates obtained from four Colombian Creole horses were subjected to programmable freezing, vitrification, and freeze-drying. After thawing or rehydration, sperm motility and kinetics were assessed through a CASA system. The mitochondrial membrane potential (ΔΨM), lipid peroxidation (LPO), and DNA fragmentation index (DFI) of the spermatozoa were assessed by flow cytometry using the DiOC6 (3), C11-Bodipy 581/591, and propidium iodide (PI) fluorescent dyes. The statistical analysis was conducted via generalized linear models, mean comparisons via the Duncan test, and a principal component analysis. A higher rate of spermatozoa with a high ΔΨM was found for freeze-drying (40.26 ± 7.79%) compared with freezing (21.82 ± 5.38%) and vitrification (5.32 ± 1.17%) (P < .05). Likewise, a higher rate of nonperoxidized viable spermatozoa (Bodipy-/PI-) was found for freeze-drying (35.98 ± 7.01%) in relation to frozen (10.34 ± 2.69%) and vitrified (7.07 ± 2.00%) sperm (P < .05). The DFI of vitrified spermatozoa (0.12 ± 0.04%) was higher when compared with the frozen (0.03 ± 0.01%) and freeze-dried (0.02 ± 0.01%) samples (P < .05). The researchers conclude that vitrification generates greater sperm alterations than freeze-drying and freezing, whereas freeze-drying produces lower LPO and higher ΔΨM for equine spermatozoa.

Directional freezing for the cryopreservation of adherent mammalian cells on a substrate

Successfully cryopreserving cells adhered to a substrate would facilitate the growth of a vital confluent cell culture after thawing while dramatically shortening the post-thaw culturing time. Herein we propose a controlled slow cooling method combining initial directional freezing followed by gradual cooling down to -80°C for robust preservation of cell monolayers adherent to a substrate. Using computer controlled cryostages we examined the effect of cooling rates and dimethylsulfoxide (DMSO) concentration on cell survival and established an optimal cryopreservation protocol. Experimental results show the highest post-thawing viability for directional ice growth at a speed of 30 μm/sec (equivalent to freezing rate of 3.8°C/min), followed by gradual cooling of the sample with decreasing rate of 0.5°C/min. Efficient cryopreservation of three widely used epithelial cell lines: IEC-18, HeLa, and Caco-2, provides proof-of-concept support for this new freezing protocol applied to adherent cells. This method is highly reproducible, significantly increases the post-thaw cell viability and can be readily applied for cryopreservation of cellular cultures in microfluidic devices.

Follicular size predicts success in artificial insemination with frozen-thawed sperm in donkeys

In asses, semen collection, cryopreservation, and artificial insemination (AI) with frozen-thawed semen have been scarcely described and success rate, particularly following AI, is reportedly low. In the absence of reliable protocols, assisted reproductive technologies cannot support the conservation efforts aimed at endangered wild ass species and domestic donkey breeds. Two experiments were conducted in this study. In experiment 1 we evaluated freezing Abyssinian donkey (N = 5, 4 ejaculates each) spermatozoa using three freezing extenders (Berliner Cryomedium + glycerol, BC+G; BotuCrio, BOTU; INRAFreeze, INRA) and two cryopreservation techniques (liquid nitrogen vapour, LNV; directional freezing, DF). Post-thaw evaluation indicated that BOTU and INRA were similar and both superior to BC+G (P ≤ 0.004 for all motility tests), and that DF was superior to LNV (P < 0.002 for all evaluation parameters). In experiment 2, relying on these results, we used Abyssinian donkey sperm frozen in BOTU and INRA by DF for AI (N = 20). Prior to AI, thawed samples were diluted in corresponding centrifugation media or autologous seminal fluids at 1:1 ratio. No difference was found between BOTU and INRA or between the addition of seminal fluids or media, all resulting in ~50% pregnancy, and no differences were noted between males (N = 4). The size of pre-ovulatory follicle was a significant (P = 0.001) predictor for AI success with 9/10 pregnancies occurring when follicular size ranged between 33.1-37.4 mm, no pregnancy when it was smaller, and only one when larger. A number of ass species face the risk of extinction. Knowledge gained in this study on the Abyssinian donkey can be customised and transferred to its closely related endangered species and breeds.

Post-thaw ATP supplementation enhances cryoprotective effect of iodixanol in rat spermatozoa

BACKGROUND

Successful cryopreservation of rat spermatozoa from various strains still remains a challenge. The objective of this study was to determine if combinations of OptiPrep™ (iodixanol) and adenosine 5'-triphosphate (ATP) can improve rat sperm function during the cryopreservation procedure.

METHODS

Epididymal rat spermatozoa were frozen under different OptiPrep™ concentrations (0, 1, 2, 3 or 4 %) and were diluted with media supplemented with or without 2 mM ATP after thawing. Post-thaw sperm motility, acrosomal membrane integrity (AMI) and mitochondrial membrane potential (MMP) were then evaluated. In addition, the effect of different OptiPrep™ concentrations on fresh and cooled rat spermatozoa was tested via motility.

RESULTS

There was no effect of OptiPrep™ on motility of fresh and cooled spermatozoa. The supplementation of 1 and 2 % OptiPrep™ increased motility of frozen spermatozoa at 10 min after thawing, while it did not improve motility of spermatozoa at 3 h after thawing in the absence of ATP. During incubation of thawed spermatozoa, the ATP addition protected time-dependent decrease in motility after thawing in OptiPrep™-treated samples. OptiPrep™ had no effect on AMI and MMP in frozen-thawed spermatozoa but combinations of OptiPrep™ and ATP improved MMP in frozen-thawed spermatozoa.

CONCLUSIONS

Iodixanol has cryoprotective effects during rat sperm freezing without any toxic effect. Moreover, the combinations of iodixanol and ATP have a beneficial role in maintaining function of frozen-thawed rat spermatozoa for long period of incubation post-thaw.

Saving wild ungulate diversity through enhanced management and sperm cryopreservation

Wild ungulates throughout the world face the impending risk of extinction. Small founding population size, lack of interest in exhibiting wild ungulates and declining space in zoos are not sustaining ex situ populations. Animals managed in ex situ collections continue to experience >20% neonate loss globally. To ensure population sustainability there is a critical need to: (1) manage ungulates in large herds, increasing mate choice and reproductive efficiency; (2) improve husbandry and genetic management; and (3) develop consistent assisted reproductive technologies, including sperm cryopreservation and AI. Recently, new models in the management of ungulates have begun to emerge. Animal managers and researchers are also beginning to exploit advances in genomics to improve genetic management of their collections. Furthermore, the past decade has witnessed significant advances particularly in semen collection and cryopreservation in numerous species. Advances in gonadal tissue cryopreservation now offer additional opportunities to preserve male genomes. The new knowledge generated is enabling the creation of genetic (sperm) banks to rescue and enhance reproductive management of wild ungulates. The present paper reviews the threats to ungulate populations, the status and relevance of animal management and biomaterial banking efforts to ensure long-term survival of these charismatic species.

The effect of the freezing curve type on bull spermatozoa motility after thawing

The objective of this work was to determine the effect of selected freezing curves on spermatozoa survivability after thawing, defined by its motility. The ejaculates of nine selected sires of the same age, breed, and frequency of collecting, bred under the same breeding conditions including handling, stabling, feeding system and feeding ratio composition, were repeatedly collected and evaluated. Sperm samples of each sire were diluted using only one extender and divided into four parts. Selected four freezing curves – the standard, commercially recommended three-phase curve; a two-phase curve; a slow three-phase curve; and a fast three-phase curve, differing in the course of temperature vs time, were applied. The percentage rate of progressive motile spermatozoa above head was determined immediately after thawing, and after 30, 60, 90, and 120 min of the thermodynamic test (TDT). Moreover, average spermatozoa motility (AMOT) and spermatozoa motility decrease (MODE) throughout the entire TDT were evaluated. Insemination doses frozen using the simpler two-phase curve demonstrated the highest motility values (+2.97% to +10.37%; P < 0.05–0.01) immediately after thawing and during the entire TDT. Concurrently, the highest AMOT (+4.37% to +8.82%; P < 0.01) was determined. The highest spermatozoa motility values were detected after thawing doses frozen by the two-phase freezing curve in eight out of nine sires. Simultaneously, a significant effect of sire individuality was clearly confirmed. Inter-sire differences of spermatozoa motility during TDT as well as AMOT and MODE were significant (P < 0.01). The findings describing both factors of interaction indicate the necessity of individual cryopreservation of the ejaculate to increase its fertilization capability after thawing.

CRYOPRESERVATION OF ONAGER (EQUUS HEMIONUS ONAGER) EPIDIDYMAL SPERMATOZOA

Genetic diversity is a primary component of adaptive evolution, and its loss or reduction can decrease the long-term survival probability of populations. Utilization of cryopreserved semen may be considered a perfect tool to improve genetic diversity, reduce inbreeding, and avoid animal translocation for breeding. The present study aimed at finding a reliable epididymal sperm freezing protocol for the critically endangered onager (Equus hemionus onager). Six testicles from three animals were processed postmortem. The effects of two transportation temperatures (22°C and 4°C; testicles submerged in saline), two cryopreservation techniques (conventional liquid nitrogen vapor freezing in straws and directional freezing in 8-ml HollowTubes(TM)), and two postthaw incubation temperatures (22°C and 37°C; evaluated after 0.5, 1, 2, and 3 hr) were tested in a 2×2×2 experimental design. Sperm samples were evaluated for motility, viability, acrosome integrity, and sperm morphology. The resulting optimal freezing protocol includes transportation of testicles at 4°C, cryopreservation by directional freezing, and, if needed, postthaw incubation at 22°C. With this combination of transportation temperature and cryopreservation technique, the authors obtained the following postthaw values normalized to prefreezing values: 60.3±8.8% motility, 60.7±13.3% viability, 75.3±9.5% acrosome integrity, and 94.7±2.9% normal morphology (excluding defects due to the epididymal origin of the sperm). After incubation at 22°C, motility values for the above combination were 40±5.7%, 30.3±5.2%, 28.3±4.4%, and 16.7±4.4% for 0.5, 1, 2, and 3 hr, respectively. In conclusion, with this protocol, good quality semen can be stored for future use in artificial inseminations when and where needed.

A comparative study of two cooling protocols on stallion sperm cryosurvival

There are many protocols for horse sperm cryopreservation, but results are inconsistent; sperm survival after freeze-thawing is usually poor; in consequence, fertility is low. The objective of this work was to see whether slow cooling before freezing to minus 3 °C instead of +5 °C, the traditional target temperature, could improve horse sperm cryosurvival, capability to carry out capacitation and the acrosome reaction induced by progesterone. Spermatozoa from five stallions were packaged in straws and slowly cooled to +5 °C. Half of the straws were frozen directly and the other half was further cooled to -3 °C before freezing. Progressive motility, viability, plasma membrane integrity, acrosome integrity and capacitation status were assessed. After thawing, there were no differences between cooling treatments on motility, viability, acrosome integrity and capacitation status; however, there was difference (P < 0.05) regarding plasma membrane integrity. Acrosome integrity decreased as incubation, without or with progesterone (2 μg ml(-1) ), progressed, but there were no differences between cooling treatments regardless of progesterone. Both capacitated and acrosome-reacted spermatozoa increased as incubation progressed, but there were no differences between cooling treatments regardless of progesterone. Slow cooling to -3 °C before freezing did not improve horse sperm cryosurvival or capability to undergo the acrosome reaction.

Directional freezing of spermatozoa and embryos

Directional freezing is based on a simple thermodynamic principle whereby the sample is moved through a predetermined temperature gradient at a velocity that determines the cooling rate. Directional freezing permits a precise and uniform cooling rate in small- and large-volume samples. It avoids supercooling and reduces mechanical damage caused by crystallisation. Directional solidification was used to date for slow and rapid freezing, as well as for vitrification of oocytes and embryos by means of the minimum drop size technique: small drops are placed on a microscope slide that is moved at high velocity from the hot base to the cold base. Sperm samples from a wide range of domestic and wild animals were successfully cryopreserved using the directional freezing method. The bovine sexed semen industry may benefit from the increased survival of spermatozoa after directional freezing.

Effect of Cholesterol and Equex-STM Addition to an Egg Yolk Extender on Pure Spanish Stallion Cryopreserved Sperm

Cholesterol and Equex-STM are frequently added to different commercial and experimental extenders improving postthawing sperm quality. Doses of 125-150 mM of cholesterol from pig liver and 0.5-0.7% of Equex-STM were evaluated in a standard eggyolk extender (Martin et al., 1979). Six ejaculates per stallion from six pure Spanish stallions (6-8 years old) were collected in Martin's extender (B) and different mixtures of 125 mM-0.5% (I), 125 mM-0.7% (II), 150 mM-0.5% (III), and 150 mM-0.7% (IV) were added to original Martin's extender. Samples were frozen in 0.5 mL straws (100 × 10(6) spermatozoa) and thawed (21 s., 37°C water bath). After thawing the following parameters were evaluated: viability (V), motility (computer assisted sperm analysis, CASA; % nonprogressive NP; % progressive MP), hipoosmotic swelling test (HOST), acrosome integrity (A), fluorescence test (FL), and resistance test (RT). Sperm quality was significantly affected by stallion (in the parameters V, VI, NP, MP, HOST, A, FL, and RT), extraction (VI, NP, MP, HOST, A, and FL), and the different combinations of Equex-STM-cholesterol (FL). We concluded that 0.5% of Equex-STM mixed with 125 mM of cholesterol has obtained better sperm quality results than those of original Martin's extender, showing a simple and economic improvement of this home-made practical seminal extender.

Porcine uterus cryopreservation: an analysis of contractile function using different uterotonics

Cryopreservation of whole organs has become increasingly successful in recent years, and establishing reliable methods for confirming the success of specific cryopreservation procedures has therefore become extremely important. On the assumption that methods such as histological evaluation do not provide definitive evidence of long-term cryopreservation and that clear signs of conserved function in an organ are good evidence of its viability, contractile function was analysed in porcine uteri (n=60), either after long-term (group A) or short-term (group B) cryopreservation and post-thaw treatment with three different uterotonics. A slow freezing protocol was used to preserve the organs. Fifteen fresh uteri were analysed similarly for contractile function, which was evaluated by measuring intrauterine pressure after administration of oxytocin, prostaglandin E(1) (PGE(1)), and carbachol. After cryopreservation, all but three uteri (95%) showed rhythmic contractions similar to those in fresh uteri except for differences in the heights of contraction peaks, with lower contractions in PGE(1) subgroup B (P<0.05). With the exception of three nonresponsive uteri in group A, there were no differences in contractility between uteri after long-term cryopreservation and fresh uteri. The results of this study thus contribute to the debate on whether slow freezing or vitrification techniques are best for whole-organ cryopreservation. In summary, (1) preservation of muscular function in porcine uteri is feasible with a slow freezing protocol; (2) measurement of contractile function following administration of uterotonics is a useful method of confirming functionality; and (3) long-term cryopreservation does not significantly impair post-thaw contractibility in comparison with fresh uteri.

Cooling and freezing of epididymal sperm in the common hippopotamus (Hippopotamus amphibius)

Knowledge concerning reproduction in common hippopotamus is scarce and in particular very little is known about male reproductive physiology and sperm cryopreservation. Testes were obtained from nine castrated bulls and sperm extracted from the epididymides of eight of these individuals. Mean ± SEM values of reproductive parameters were: testicular weight (including epididymis and tunicas)--275.9 ± 54.1 g, total sperm motility--88.1 ± 4.2%, total cells extracted--11.0 ± 3.6 × 10(9), intact acrosome--87.7 ± 1.8%, intact sperm morphology--51.6 ± 4.1%, and, for 3 individuals, hypoosmotic swelling test for membrane integrity-83.3 ± 1.8%. Chilled storage extenders tested were Berliner Cryomedium (BC), Biladyl(®), modification of Kenney modified Tyrode's medium (KMT), and Human Sperm Refrigeration Medium (HSRM). Extender had significant effect on post-dilution motility and motility and intact morphology after 4h and 24h at 4°C (P ≤ 0.007 for all). Berliner Cryomedium and HSRM were superior to Biladyl(®) and KMT. Freezing extenders tested were BC with either 6% dimethyl sulfoxide (Me(2)SO), or 5%, 7%, or 10% glycerol. Post-thaw motility was < 5% in 3/7 bulls in all extenders. When frozen in BC with 6% Me(2)SO, one bull had 15% post-thaw motility and 3/7 had 20 to 60%. In glycerol, 3/7 had 15-30% post-thaw motility in 5%, 2/7 in 7%, and 1/7 in 10%. The extender had significant effect on post-chilling motility (P = 0.008), post-thaw morphology (P = 0.016), and motility 30 min after thawing (P = 0.015). Berliner Cryomedium with 6% Me(2)SO or 7% glycerol were the freezing extenders of choice. Information obtained in this study allows initiation of cryobanking of sperm from the common hippopotamus which is of particular importance for genetically valuable individuals.

Preservation of beluga (Delphinapterus leucas) spermatozoa using a trehalose-based cryodiluent and directional freezing technology

A beluga (Delphinapterus leucas) sperm preservation method was developed for use in genome banking and AI. In Study 1, glycerol-based cryodiluents (modified BF5F and modified Platz Diluent Variant (PDV)) were unable to maintain adequate progressive motility using straws (fast and slow freezing rate (FR)) or pellets (slow FR). Neither freezing method nor FR affected in vitro sperm characteristics (P > 0.05), but retention of prefreeze progressive motility following thawing was greater (P < 0.05) for BF5F (21%) than PDV (15%). In Study 2, examining the effects of straw freeze–thawing using BF5F with glycerol (1 and 3%, v/v) or trehalose (46 and 91 mM) on sperm characteristics, samples cryopreserved in trehalose exhibited superior (P < 0.05) in vitro parameters compared with their glycerol-treated counterparts. In Study 3, compared with a straw method, directional freezing using 91 mM trehalose enhanced (P < 0.05) sperm characteristics, with samples retaining 38%, 75% and 61% of their prefreeze progressive motility, curvilinear velocity and viability, respectively. A higher (P < 0.05) proportion of motile spermatozoa displayed rapid velocity after directional (21 ± 1%) compared with straw (12 ± 3%) freezing. Systematic development of a cryodiluent and the use of directional freezing resulted in beluga spermatozoa exhibiting adequate post-thaw quality for genome banking and use in AI.

Do physical forces contribute to cryodamage?

To achieve the ultimate goal of both cryosurgery and cryopreservation, a thorough understanding of the processes responsible for cell and tissue damage is desired. The general belief is that cells are damaged primarily due to osmotic effects at slow cooling rates and intracellular ice formation at high cooling rates, together termed the "two factor theory." The present study deals with a third, largely ignored component--mechanical damage. Using pooled bull sperm cells as a model and directional freezing in large volumes, samples were frozen in the presence or absence of glass balls of three different diameters: 70-110, 250-500, and 1,000-1,250 microm, as a means of altering the surface area with which the cells come in contact. Post-thaw evaluation included motility at 0 h and after 3 h at 37 degrees C, viability, acrosome integrity, and hypoosmotic swelling test. Interactions among glass balls, sperm cells, and ice crystals were observed by directional freezing cryomicroscopy. Intra-container pressure in relation to volume was also evaluated. The series of studies presented here indicate that the higher the surface area with which the cells come in contact, the greater the damage, possibly because the cells are squeezed between the ice crystals and the surface. We further demonstrate that with a decrease in volume, and thus increase in surface area-to-volume ratio, the intra-container pressure during freezing increases. It is suggested that large volume freezing, given that heat dissipation is solved, will inflict less cryodamage to the cells than the current practice of small volume freezing.

Ovarian function 6 years after cryopreservation and transplantation of whole sheep ovaries

Whole ovary cryopreservation and transplantation has been proposed as a method for preserving long-term ovarian function. This work reports ovarian function 6years post transplantation of frozen-thawed whole sheep ovaries. Three 9-month-old Assaf sheep underwent unilateral oophorectomy to provide organs for the experiments. After perfusing with cold University of Wisconsin solution supplemented with 10% dimethyl sulphoxide, ovaries were cryopreserved using unidirectional solidification freezing technology. After thawing, ovaries were re-perfused and re-transplanted orthotopically by microvascular re-anastomosis, to the contralateral ovarian pedicle after removing the remaining ovary. Six years following transplantation and after inducing superovulation, the sheep were killed and the ovaries analysed. Two ovaries had normal size and shape showing some recent corpora lutea, while the third showed atrophic changes. A total of 36 antral follicles were counted by transillumination and four germinal vesicle oocytes were aspirated and matured in vitro to metaphase II. Serum progesterone concentrations were indicative of ovulatory activity in one of the three sheep. Histological evaluations revealed normal tissue architecture, intact blood vessels and follicles at various stages. Currently, this is the longest recorded ovarian function after cryopreservation and re-transplantation. Cryopreservation of whole ovaries, using directional freezing combined with microvascular anastomosis, is a promising method for preserving long-term reproductive capacity and endocrine function.

Protective effects of iodixanol during bovine sperm cryopreservation

The aim of cryopreservation is to maintain cellular integrity, thereby enabling resumption of proper biological functioning after thawing. Here we propose OptiPrep (60% iodixanol in water) as a protectant during sperm cryopreservation using pooled bull semen as the model. We evaluated OptiPrep concentration effect and its relation to cryopreservation by comparing frozen-thawed and chilled samples. Semen, extended in Andromed with 0 (control), 1.25%, 2.5%, and 5% OptiPrep, was compared after either chilling or freezing in large volume by directional freezing. Sample evaluation included sperm motility upon thawing and after 3h incubation at 37 degrees C for frozen-thawed samples and after 3h and 6h of chilling for chilled samples; viability, acrosomal integrity, and hypoosmotic swelling were also tested for frozen-thawed and chilled samples. Chilled samples with 5% OptiPrep showed inferior viability (P=0.047) and 3h motility (P=0.017) relative to that for chilled samples with 2.5% OptiPrep and inferior viability (P=0.042), acrosomal integrity (P=0.045), and 0h motility (P=0.024) relative to that for chilled samples with 1.25% OptiPrep. The 1.25%, 2.5%, and control samples did not differ. In frozen-thawed samples, 2.5% OptiPrep was superior to all other concentrations for 3h motility (control, P=0.007; 5% OptiPrep, P=0.005; 1.25% OptiPrep, P=0.004) and to 1.25% OptiPrep for acrosomal integrity (P=0.001). In a search for a protection mechanism, we measured glass transition temperature (T(g)) of Andromed and of Andromed with 1.25%, 2.5%, and 5% OptiPrep. Andromed (-58.78 degrees C) and 1.25% OptiPrep (-58.75 degrees C) groups had lower mean T(g) than that of the 2.5% (-57.67 degrees C) and the 5% (-57.10 degrees C) groups. Directional cryomicroscopy revealed that the presence of iodixanol alters ice crystal formation into an intricate net of dendrites. Thus, iodixanol appears to possess cryoprotective properties by helping spermatozoa maintain motility and membrane integrity, possibly through altering ice crystals formation into a more hospitable environment and increasing the glass transition temperature.

Animal models for fertility preservation in the male

Fertility preservation in the male is routinely focused on sperm. In clinical and veterinary settings, cryopreservation of sperm is a widely used tool. However, the goals for male fertility preservation differ between experimental models, maintenance of livestock, conservation of rare species, and fertility protection in men. Therefore very different approaches exist, which are adapted to the specialized needs for each discipline. Novel tools for male fertility preservation are explored targeting immature germ cells in embryonic or immature testes. Many options might be developed to combine germline preservation and generation of sperm ex vivo leading to interesting new perspectives. This review highlights current and future options for male fertility preservation with a special focus on animal models and a consideration of the various disciplines in need of novel tools.