Improved sperm cryosurvival in diluents containing amides versus glycerol in the Przewalski's horse (Equus ferus przewalskii)

Insights into alternative cryoprotectants to freeze sperm of domestic cats

Globalization and habitat destruction pose a significant threat to wildlife felids. Even though conservation banks for genetic materials have been created, the sperm cryopreservation with minimal cell damage is still a great challenge. Thus, this study aimed to compare the effects of two commercial extenders with different concentrations of alternative cryoprotectants on thawed sperm quality of domestic cats. Five adult cats were anaesthetized (using a combination of 40 μg/kg medetomidine associated to 5 mg/kg ketamine), and the semen was collected by electroejaculation (electrical stimulation of 2-3 V). Semen samples were evaluated for sperm characteristics (kinetics, morphology, membrane integrity and morphometry). Subsequently, they were sorted into two aliquots and centrifuged. The aliquots were added to a commercial extender containing 3% glycerol and 2% methylformamide (extender I) or 2% glycerol and 3% methylformamide (extender II), frozen, thawed (37°C/30 s) and reevaluated. Comparatively, the sperm kinetics and membrane integrity of fresh semen were higher (p < .002) than frozen samples in extender I and II. Total and progressive motility were lowest in the thawed samples. However, the subjective analysis indicated high sperm motility, since the kinetics evaluation was impaired by the low cell number in the thawed samples. There were no differences in sperm morphology between the groups. In the sperm morphometric analysis, a significant difference (p = .04) was identified in the length of the intermediate piece in extender II samples compared with fresh and extender I. Thus, it can be concluded that although the concentrations tested did not maintain the kinetic parameters and membrane integrity of spermatozoa after thawing, the extender with a lower concentration of glycerol was less toxic for maintaining the midpiece length.

Sperm Quality Assessment in Stallions: How to Choose Relevant Assays to Answer Clinical Questions

Stallion sperm analysis is indicated for infertility diagnosis, pre-sale expertise, production of fresh or frozen doses, and frozen straw quality control. Various collection methods are described, and numerous assays can be performed on semen. Determining an approach for each of these cases is challenging. This review aims to discuss how to obtain relevant clinical results, answering stallion owners' concerns. Semen can be collected with an artificial vagina on a phantom or a mare, by electro-ejaculation under anesthesia, or after pharmacological induction. The collection method influences the semen volume and concentration, while the total sperm number depends on the testicular production and collection frequency. In the seminal plasma, acidity, pro-oxidant activity, and some enzymes have repercussions for the semen quality and its conservation. Moreover, non-sperm cells of seminal plasma may impact semen conservation. Motility analysis remains a core parameter, as it is associated with fresh or frozen dose fertility. Computer-assisted motility analyzers have improved repeatability, but the reproducibility between laboratories depends on the settings that are used. Morphology analysis showing spermatozoa defects is useful to understand production and maturation abnormalities. Staining of the spermatozoa is used to evaluate viability, but recent advances in flow cytometry and in fluorochromes enable an evaluation of multiple intracellular parameters. Spermatozoa protein expression already has clinical applications, for example, as a fertility and freezing ability predictor. At present, stallion semen analysis ranges from macroscopic evaluation to assessing spermatozoa proteins. However, clinically, all these data may not be relevant, and the lack of standardization may complicate their interpretation.

Cellular and Molecular Consequences of Stallion Sperm Cryopreservation: Recent Approaches to Improve Sperm Survival

Cryopreservation of stallion semen does not achieve the post-thaw quality or fertility results observed in other species like cattle. There are many reasons for this, but the membrane composition and intracellular changes in stallion sperm predispose them to low resistance to the cooling, freezing, and subsequent thawing process. Damage to the sperm results from different processes activated during cryopreservation, including oxidative stress, apoptosis, and structural modifications in the sperm membrane that increase the deleterious effect on sperm. In addition, significant individual variability is observed among stallions in the ability of sperm to survive the freeze-thaw process. Recent advances in genomics, transcriptomics, proteomics, metabolomics, and epigenetics are making it possible to advance our understanding of the cellular and molecular processes involved in the cryopreservation process, opening new possibilities for improvement. This review addresses the ongoing research on stallion semen cryopreservation, focusing on the cellular and molecular consequences of this procedure in stallions and discusses the new tools currently available to increase the tolerance of equine spermatozoa to freeze-thaw.

Transcriptome Analysis Reveals Key Gene Expression Changes in Blue Catfish Sperm in Response to Cryopreservation

The hybrids of female channel catfish (Ictalurus punctatus) and male blue catfish (I. furcatus) account for >50% of US catfish production due to superior growth, feed conversion, and disease resistance compared to both parental species. However, these hybrids can rarely be naturally spawned. Sperm collection is a lethal procedure, and sperm samples are now cryopreserved for fertilization needs. Previous studies showed that variation in sperm quality causes variable embryo hatch rates, which is the limiting factor in hybrid catfish breeding. Biomarkers as indicators for sperm quality and reproductive success are currently lacking. To address this, we investigated expression changes caused by cryopreservation using transcriptome profiles of fresh and cryopreserved sperm. Sperm quality measurements revealed that cryopreservation significantly increased oxidative stress levels and DNA fragmentation, and reduced sperm kinematic parameters. The present RNA-seq study identified 849 upregulated genes after cryopreservation, including members of all five complexes in the mitochondrial electron transport chain, suggesting a boost in oxidative phosphorylation activities, which often lead to excessive production of reactive oxygen species (ROS) associated with cell death. Interestingly, functional enrichment analyses revealed compensatory changes in gene expression after cryopreservation to offset detrimental effects of ultra-cold storage: MnSOD was induced to control ROS production; chaperones and ubiquitin ligases were upregulated to correct misfolded proteins or direct them to degradation; negative regulators of apoptosis, amide biosynthesis, and cilium-related functions were also enriched. Our study provides insight into underlying molecular mechanisms of sperm cryoinjury and lays a foundation to further explore molecular biomarkers on cryo-survival and gamete quality.

Addition of Reduced Glutathione (GSH) to Freezing Medium Reduces Intracellular ROS Levels in Donkey Sperm

In donkeys, the use of frozen-thawed sperm for artificial insemination (AI) leads to low fertility rates. Furthermore, donkey sperm produce a large amount of reactive oxygen species (ROS), and post-AI inflammation induces the formation of neutrophil extracellular traps (NETosis), which further generates many more ROS. These high ROS levels may induce lipid peroxidation in the sperm plasma membrane, thus affecting its integrity. Enzymatic and non-enzymatic antioxidants, mainly found in the seminal plasma (SP), are responsible for maintaining the redox balance. However, this fluid is removed prior to cryopreservation, thereby exposing sperm cells to further oxidative stress. The exogenous addition of antioxidants to the freezing medium can reduce the detrimental effects caused by ROS generation. Therefore, the aim of this study was to evaluate how the addition of different reduced glutathione (GSH) concentrations (control, 2 mM, 4 mM, 6 mM, 8 mM, and 10 mM) to fresh sperm affect their cryotolerance. Total and progressive motility, kinematic parameters and motile sperm subpopulations were significantly (p < 0.05) different from the control in treatments containing 8 mM and 10 mM GSH, but not at lower concentrations. Plasma and acrosome membrane integrity, mitochondrial membrane potential (MMP) and intracellular superoxide levels (O₂⁻) were not affected (p > 0.05) by any GSH concentration. Interestingly, however, the addition of 8 mM or 10 mM GSH reduced (p < 0.05) the percentages of viable sperm with high overall ROS levels compared to the control. In conclusion, frozen-thawed donkey sperm are able to tolerate high GSH concentrations, which differs from what has been observed in other species. This antioxidant capacity suggests that ROS could be important during post-AI and that the impact of using exogenous antioxidants like GSH to improve the sperm resilience to freeze-thawing is limited in this species.

Recent Progress in Spermatology Contributing to the Knowledge and Conservation of Rare and Endangered Species

There is a remarkable diversity in the animal kingdom regarding mechanisms underlying the production, maturation, structure, and function of sperm cells. Spermatology studies contribute to the knowledge of species diversity and also provide information about individual or population fitness. Furthermore, this fundamental research is required before collected spermatozoa can be used for conservation breeding, including assisted reproduction and cryobanking. This article aims to (a) review the most recent knowledge on sperm morphology and function in wild animal species, (b) analyze how this knowledge can be used to save species in their natural habitat or ex situ, and (c) propose future scientific directions in wildlife spermatology that could positively impact animal conservation. Variations in sperm structure and performance within and between species have multiple origins and significance. This collective body of knowledge enables the design and implementation of conservation strategies and action plans that integrate several disciplines. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Case Report: Suppression of Harem Stallion Behavior and Fertility Following Anti-Gonadotropin-Releasing Hormone Vaccination of a Captive Wild Przewalski's Horse (Equus ferus przewalskii)

This report describes an option to modulate the testicular function of wild horses and field methods to assess it. Non-surgical castration of a captive wild Przewalski's stallion with anti-gonadotropin-releasing hormone (GnRH) immunization was performed by sub-cutaneous injection of two doses of 450 μg (3 ml) of GnRH conjugated to diphtheria toxin, further repeated every 6 months. Semen quality was assessed after collection by electro-ejaculation under general anesthesia. Endocrine and behavioral consequences were studied during a 2-year follow-up period. The procedure of electro-ejaculation was safe and effective to collect spermatozoa. Motility was low but was improved by a significant dilution of sample (1v/4v−1v/5v) after collection. Immuno-neutering resulted in a decrease of the total spermatozoa number and motility 1 month after primary vaccination. However, infertility could not yet be guaranteed. Six months post-vaccination, serum testosterone concentrations had decreased and the treated stallion had lost his harem stallion role. Moreover, at the same time, the total spermatozoa number was near zero with no motile spermatozoa, and offspring was no longer observed. As a conclusion, electro-ejaculation under general anesthesia is suitable on wild horses to obtain spermatozoa that should be washed or largely diluted before use for artificial insemination (AI) programs. Anti-GnRH immuno-neutering protocol led to a dramatic decrease of spermatozoa number, motility, and testosterone production. This also induced deep changes in the social structure of the band. Such technique could be considered as an alternative to surgical castration in wild horses.

Cholesterol Loaded Cyclodextrin Supplementation Enhances the Cholesterol-to-Phospholipid Ratio and Diminishes Oxidative Stress in Jack Spermatozoa During Cryopreservation

The present study was conducted with the hypothesis that addition of cholesterol to the extender would stabilize the sperm membranes by increasing the cholesterol-to-phospholipid (C:P) ratio and would result in an improved post-thaw semen quality and reduce oxidative stress in the jack (Martina franca) semen. Forty-eight ejaculates from six jacks were collected and analyzed for the present study. The freshly collected semen sample of each jack stallion was divided into five equal fractions after addition of the primary extender without cholesterol-loaded cyclodextrin (CLC) (C) and with 1, 1.5, 2, and 3 mg/mL CLC to obtain 120 × 10⁶ sperm/mL spermatozoa concentration. The semen was cryopreserved using customized freezing protocols. Evaluation of seminal parameters, the C:P ratio, and the oxidative status of jack spermatozoa was analyzed at all stages of cryopreservation. The oxidative status in the jack semen was evaluated by measuring malondialdehyde, glutathione and total antioxidant capacity levels. The results indicated that the mean percent values for various seminal quality parameters and the oxidative parameters were found to be significantly higher (P < .05) in CLC-treated groups with the highest values for 2 mg of CLC/120 × 10⁶ spermatozoa. In conclusion, the present study revealed that the supplementation of CLC before cryopreservation has significantly reduced the oxidative stress and also increased the C:P ratio during semen cryopreservation process. Furthermore, a reduction in lipid peroxidation levels, reduced damage to the sperm plasma and acrosome membranes and improvement in the post-thaw sperm integrity as well as stability were recorded.

Effect of glycerol, n, n-dimethylformamide and n-methyl-2-pyrrolidone on rabbit sperm stored at 4 °C and 16 °C

Artificial insemination with cooled semen is the most common practice in rabbit farms and any improvement on it helps to increase the efficiency and productivity of rabbit meat farms. Therefore, the aim of this study was to assess whether different cryoprotectant agents (CPA) as glycerol, N, N-Dimethylformamide (DMF) and N-Methyl-2-Pyrrolidone (NMP) can improve cooled rabbit sperm quality stored at 4ºC and 16ºC. Sperm samples were diluted with INRA 96^® (Extender A), INRA 96^® with 6% glycerol (Extender B) or 6% DMF (Extender C) or 6% NMP (Extender D) respectively and stored at 4ºC and 16ºC. Samples were then analysed at 4, 24, 48 and 72 hours after refrigeration by integrated sperm analysis system (ISAS^®), eosin-nigrosin stain (vitality), hypo-osmotic swelling test (HOS test) and acrosome integrity test. Extender C showed higher percentage of motility, vitality and HOS test than extender B and D (p<0.05). Whereas sperm quality decreased over time (p<0.05), data showed that the addition of DMF kept the motility and sperm plasma membrane integrity after 24 hours of storage better than other diluents. These results suggest that the addition of DMF to INRA 96^® exerts a protective effect on the membrane of spermatozoa improving seminal quality.

Quality assessment of cryopreserved New Zealand white rabbit spermatozoa in INRA-82 extender containing different cryoprotectants

<p>The present study aimed to evaluate the effect of supplementation of INRA-82 semen extender with different cryoprotectants (dimethyl sulphoxide; DMSO vs. dimethyl formamide; DMF) on the quality of white New Zealand rabbit buck spermatozoa. We also investigated the possible association between the synergistic action of DMSO and DMF and their relation with INRA-82 extender composition. Semen was collected and pooled from 8 adult rabbit bucks. Pooled semen samples were diluted 1:1 with INRA-82 extender supplemented with DMSO 8%, DMF 8% or a combination of DMSO 4% and DMF 4%. The diluted semen samples were cryopreserved in 0.25 plastic straws. After thawing, progressive motility, sperm viability, sperm abnormalities, membrane integrity, acrosome status, viability index and DNA integrity were evaluated. The results showed that dilution of rabbit buck semen in INRA-82 supplemented with DMSO and DMF (4% each) before freezing significantly (<em>P</em>&lt;0.05) improved sperm motility (42.00%), percentage of live spermatozoa (45.30%), proportions of spermatozoa with intact acrosome (59.75%) and percentage of spermatozoa with non-fragmented DNA (86.04%), compared to those diluted in INRA-82 supplemented either with DMSO 8% (+9, +10, +5 and +7 percentage points, respectively) or with DMF 8% alone (+18 +18, +12 and +9 percentage points, respectively). In conclusion, dilution of rabbit buck semen before freezing with INRA-82 extender supplemented with a combination of DMSO 4% and DMF 4% improved quality of frozen-thawed New Zealand White rabbit spermatozoa. Furthermore, our results also suggest that supplementation of INRA-82 with DMSO or with DMF alone at higher concentrations deteriorates the sperm quality.</p>

Strong Heterogeneity in Advances in Cryopreservation Techniques in the Mammalian Orders

Between 1970 and 2012, vertebrate abundance has declined by 58% with an average annual decline of 2%, calling for serious action to prevent a mass extinction and an irreversible loss of biodiversity. Cryobanks and cryopreservation have the potential to assist and improve ex situ and in situ conservation strategies by storing valuable genetic material. A great deal of studies concerning cryopreservation have been performed within the class Mammalia, although no systematic overview has previously been presented. The objective of this study is therefore to evaluate the status, pattern and future of cryopreservation within Mammalia. A strong disproportional distribution of studies in examined orders is displayed. For the majority of examined orders less than 10% of species has been examined. However, the cryopreservation of germplasm has in several cases been successful and resulted in successful applications of assisted reproductive techniques (ARTs). Various obstacles are associated with the development of cryopreservation protocols, and among them the most prominent is interspecific differences in cryotolerance. Extrapolation of protocols in closely related species is considered the most applicable procedure, and a future supplement to overcome this problem is the examination and comparison of cryobiological traits. Successful protocols have been developed for the vast majority of domesticated mammals, which gives incentive for the further extrapolation of protocols in threatened species.

First cryopreservation of phyllostomid bat sperm

Bats, the second-largest mammalian order, are widely distributed and provide crucial ecosystem services. Their reproductive biology comprises noteworthy characteristics, such as long-term sperm storage, delayed implantation or even delayed fetal development. The understanding of these mechanisms remains limited. Research in reproductive biology may become crucial for the conservation of endangered bat species. Indeed, the IUCN Red List of Threatened Species currently lists 76 bat species as endangered or critically endangered, for which conservation measures should be taken. The development of assisted reproductive technologies (ART) in bats would thus open new perspectives. In this context we here describe the first successful cryopreservation of bat sperm in the Seba's short-tailed bat (Carollia perspicillata). Epididymal sperm of 30 males was pooled in 6 sample sets and diluted using four different cryo-diluents: Canifreeze, modified Canifreeze, BotuCrio^® and Test egg yolk extender. Glycerol and a mixture of glycerol and methylformamide were used as cryoprotectants. Best post-thaw results were achieved when sperm was diluted in Test egg yolk extender containing a mixture of glycerol and methylformamide as cryoprotectant. Post-thaw sperm motility, progressive motility and acrosome integrity of 42.0 ± 3.4%, 28.3 ± 6.3% and 87.7 ± 1.7%, respectively were superior to all other variants tested. It remains to be determined if the post-thaw quality of cryopreserved bat spermatozoa achieved in this study is sufficient for the use in artificial inseminations and produces acceptable pregnancy rates. Successful cryopreservation of spermatozoa in C. perspicillata may serve as the first model to establish gamete rescue programs and develop ART in other, critically endangered bat species.

Effects of seminal plasma and different cryoprotectants on rabbit sperm preservation at 16°C

The purpose of this research was to assess whether the presence of seminal plasma (SP) can improve sperm quality of rabbit spermatozoa stored at 16°C for 72 h and moreover evaluate the cryoprotectant effects of glycerol, N-N-Dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). Semen samples were pooled and divided in eight fractions. Four of them were diluted with INRA (extender A), INRA with 6% glycerol (extender B), INRA with 6% DMF (extender C), or INRA with 6% NMP (extender D), respectively. The other four fractions were centrifuged, and the supernatant was removed in order to eliminate SP. Each sample was then resuspended with extender A, B, C, or D, respectively. All samples were stored at 16°C and analysed at 4, 24, 48, and 72 h by ISAS^®, vitality test, HOS test, and acrosome integrity test. After analyse of the results, SP samples showed a significantly higher percentage (P=0.020) in the HOS test (71.9 ± 1.6%) than non-SP samples (66.5 ± 1.6%). Non-SP samples had better results for kinematic parameters. Extenders A and C showed great results for the percentage of motile spermatozoa (63.1 ± 4.3% and 63.4 ± 3.7%, respectively), vitality (88.9 ± 2.6% and 87.7 ± 2.7%, respectively), and HOS test (68.9 ± 1.4% and 75.2 ± 1.4%, respectively). Extenders B and D showed worse data for sperm quality. These results suggest that SP has a protective effect on rabbit sperm membranes and maintains better sperm motility. The addition of glycerol and NMP to INRA does not improve rabbit sperm quality; nevertheless, the DMF cryoprotectant exerts a protective effect on the membrane of spermatozoa, improving seminal quality during rabbit sperm preservation at 16°C.

Biobanking efforts and new advances in male fertility preservation for rare and endangered species

Understanding and sustaining biodiversity is a multi-disciplinary science that benefits highly from the creation of organized and accessible collections of biomaterials (Genome Resource Banks). Large cryo-collections are invaluable tools for understanding, cataloging, and protecting the genetic diversity of the world's unique animals and plants. Specifically, the systematic collection and preservation of semen from rare species has been developed significantly in recent decades with some biobanks now being actively used for endangered species management and propagation (including the introduction of species such as the black-footed ferret and the giant panda). Innovations emerging from the growing field of male fertility preservation for humans, livestock species, and laboratory animals are also becoming relevant to the protection and the propagation of valuable domestic and wild species. These new approaches extend beyond the “classical” methods associated with sperm freezing to include testicular tissue preservation combined with xenografting or in vitro culture, all of which have potential for rescuing vast amounts of unused germplasm. There also are other options under development that are predicted to have a high impact within the next decade (stem cell technologies, bio-stabilization of sperm cells at ambient temperatures, and the use of genomics tools). However, biobanking efforts and new fertility preservation strategies have to expand the way beyond mammalian species, which will offer knowledge and tools to better manage species that serve as valuable biomedical models or require assistance to reverse endangerment.

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.

Effect of single-layer centrifugation or washing on frozen-thawed donkey semen quality: Do they have the same effect regardless of the quality of the sample?

The aims of this study were to determine the sperm quality of frozen-thawed donkey sperm samples after single-layer centrifugation (SLC) using Androcoll-E in comparison to sperm washing or no centrifugation and to determine if the effect on the sperm quality after SLC or sperm washing depends on the quality of the sample. Frozen-thawed sperm samples from Andalusian donkeys were divided into three aliquots, and they were processed using three different techniques after thawing: uncentrifuged diluted control (UDC), sperm washing (SW), and SLC. Afterward, sperm quality index was estimated by integrating all parameters (total and progressive sperm motility, membrane integrity, and DNA fragmentation) in a single value. The relationship between the sperm quality of thawed UDC samples and the effect on sperm parameters in SW and SLC-selected samples was assessed. Sperm quality index was significantly higher (P < 0.001) in SLC (0.8 ± 0.0) samples than that in UDC (0.6 ± 0.0) and SW (0.6 ± 0.0) samples, regardless of the sperm quality index after thawing of the sperm sample. In conclusion, SLC of frozen-thawed donkey spermatozoa using Androcoll-E-Small can be a suitable procedure for selecting frozen-thawed donkey sperm with better quality, in particular in those samples where an improvement in motility is needed.

Differences in serum protein 2D gel electrophoresis patterns of Przewalski's (Mongolian wild horse) and thoroughbred horses

The objective of this study was to assess differences in serum protein expression profiles of Przewalski's (Mongolian wild horse) and thoroughbred horses using proteome analysis. The serum proteins were separated by two-dimensional electrophoresis (2-DE) and five different gene products were identified. Proteins represented by the five spots were identified by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS)/MS technology. The identities of all proteins were deduced based on their similarity to proteins in the human plasma protein database. Three proteins (a haptoglobin-2 alpha glycoprotein and two haptoglobin-2beta glycoproteins with different accession numbers) were downregulated in Przewalski's horse sera compared to thoroughbred horse sera. Moreover, two proteins (tetraspanin-18 and pM5) were upregulated in Przewalski's horses compared to thoroughbred horses. Haptoglobin-2 alpha and haptoglobin-2beta may serve as candidate molecules in future studies of inflammation, coagulation, immune modulation and pro-oxidant and antioxidant activity with consequential effects on the entire metabolism of the horse.