Heat shock protein A8 stabilizes the bull sperm plasma membrane during cryopreservation: Effects of breed, protein concentration, and mode of use

Use of a sperm-Hyaluronan binding assay for evaluation of sperm quality in dromedary camels

The objective of this study was to assess the ability of camel spermatozoa to bind in the Hyaluronan Binding Assay (HBA), to determine if conventional sperm quality parameters, in vitro fertilization capacity, and precursor of A-Kinase Anchoring Protein 4 (proAKAP4) values correlate with HBA results. The potential to predict post-thaw fertilization performance from HBA for fresh dromedary camel sperm was also evaluated. Semen samples were collected and assessed both fresh and post thawing, at 0 h and 1.5 h. Conventional semen analysis, HBA, and a proAKAP4 biomarker-test were used to validate sperm quality. A heterologous sperm penetration assay using zona pellucida-free goat oocytes was used to assess in vitro sperm fertilizing capacity. The results showed that dromedary camel spermatozoa bound to hyaluronan with no correlation between results from fresh samples and after thawing. Furthermore, the proAKAP4 test results showed a negative correlation with HBA at 0 h after thawing (r = - 0.62; P = 0.03). In the conventional analysis, only progressive motility (r = 0.65; P = 0.02) and straightness correlated with HBA for fresh semen (r = 0.69; P = 0.01). In the sperm penetration assay, a moderate but non-significant correlation was identified between fresh sperm HBA and penetration (r = 0.52; P = 0.07). In conclusion, results suggested that HBA can be used to assess camel sperm properties, but further investigation is needed to understand its correlation with other sperm quality parameters. The HBA score from fresh dromedary camel sperm was unable to predict post-thaw fertilization performance.

The In Vitro Evaluation of Rooster Semen Pellets Frozen with Dimethylacetamide

Sperm cryopreservation is an effective technique for conserving animal genetic diversity and transmitting superior genetic backgrounds, maintained via a non-invasive sampling and collection of huge quantities of sperm. Nevertheless, cryopreservation in avian species is not commercially viable because of the rooster sperm's susceptibility to damage. This study aims to estimate the impact of dimethylacetamide (DMA) as a cryoprotectant at different levels (3%, 6%, or 9%) on the post-thawed sperm quality, motility, antioxidant-biomarkers, and the expression of anti-freeze related genes. Semen samples were collected twice a week from twelve roosters aged 40 wk, weighing 3400 ± 70 g, and belonging to the Cairo-B2 chicken strain. Fresh semen samples were rapidly appraised, pooled, diluted with two volumes of a basic extender, and divided equally into three groups. The diluted groups were chilled at -20 °C for 7 min, then gently supplemented with 3, 6, or 9% pre-cooled DMA and equilibrated at 5 °C for a further 10 min. Semen pellets were formed by pipetting drops 7 cm above liquid nitrogen (LN₂), which were then kept inside cryovials in the LN₂. Thawing was performed 2 months later by taking 3-4 pellets of the frozen semen into a glass tube and warming it in a water bath for 8 s at 60 °C. The results showed that 3% DMA increased the proportion of total motile sperm, progressivity, viability, and plasma membrane integrity (%) compared to the 6% and 9% DMA groups. The lipid peroxidation and antioxidant enzyme activity were improved in the 3% group. At the same time, some anti-freeze-related genes' (including ras homolog family member A (RHOA), heat shock protein 70 (HSP70), and small nuclear ribonucleoprotein polypeptide A (SNRPA1)) expressions were upregulated within the 3% DMA group relative to other groups. In conclusion, the 3% DMA group maintained higher post-thawed sperm quality than the other tested groups.

Molecular Markers: A New Paradigm in the Prediction of Sperm Freezability

For decades now, sperm cryopreservation has been a pillar of assisted reproduction in animals as well as humans. Nevertheless, the success of cryopreservation varies across species, seasons, and latitudes and even within the same individual. With the dawn of progressive analytical techniques in the field of genomics, proteomics, and metabolomics, new options for a more accurate semen quality assessment have become available. This review summarizes currently available information on specific molecular characteristics of spermatozoa that could predict their cryotolerance before the freezing process. Understanding the changes in sperm biology as a result of their exposure to low temperatures may contribute to the development and implementation of appropriate measures to assure high post-thaw sperm quality. Furthermore, an early prediction of cryotolerance or cryosensitivity may lead to the establishment of customized protocols interconnecting adequate sperm processing procedures, freezing techniques, and cryosupplements that are most feasible for the individual needs of the ejaculate.

Cryopreservation of Yak Semen: A Comprehensive Review

An urgent need to boost the sustainability and efficiency of animal production exists, owing to the growing global population. Enhancing the global fertility of animals, especially cattle, is essential to ameliorate this issue. Artificial insemination and sperm cryopreservation have a considerable and favorable influence on the quantity and quality of the cattle produced. Sperm cryopreservation is crucial for livestock production because it promotes and accelerates genetic diversity and the worldwide dispersion of animals with enhanced genetics. Owing to the importance of cryobiology in reproductive technologies, researchers are developing new approaches, and they are testing cryoprotectant drugs to enhance sperm cryosurvival. However, the viability of sperm after freezing is low and widely varies across breeding yaks. These faults are crucial because they impede advances in reproductive biotechnology and the study of mammalian gametes at a fundamental level. Using chemicals, researchers have developed and enhanced various extenders with varying degrees of efficiency to reduce cryodamage and oxidative stress. In this article, we review the cryopreservation of yak semen, the development of extenders, the difficulties faced during cryopreservation, and the evaluation of semen quality using various methodologies. This review might be helpful for researchers exploring semen cryopreservation in the future, as demand for enhanced cryopreservation exists to boost the post-thaw viability and fertility of sperm.

Advances in sperm cryopreservation in farm animals: Cattle, horse, pig and sheep

Sperm cryopreservation is one of the most important procedures in the development of biotechnologies for assisted reproduction. In some farm animals, the use of cryopreserved sperm has so many benefits for which relevance has become more evident in recent decades. Values for post-thaw sperm quality, however, are variable among species and within individuals of the same species. There is no standardized methodology for each of the stages of the cryopreservation procedure (andrological examination, semen collection, dilution, centrifugation, resuspension of the pellet with the freezing medium, packaging, freezing and post-thaw sperm evaluation), which also contributes to differences among studies. Cryotolerance markers of sperm and seminal plasma (SP) have been evaluated for prediction of ejaculate freezability. In addition, in previous research, there has been a focus on supplementing cryopreservation media with different substances, such as enzymatic and non-enzymatic antioxidants. In most studies, inclusion of these substances have led to improved post-thaw sperm quality and fertilizing capacity as a result of minimizing the adverse effects on sperm structure and function. Another approach is the use of different cryoprotectants. The aim with this review article is to provide an update on sperm cryopreservation in farm animals. The main detrimental effects of cryopreservation are described, including the negative repercussion on reproductive performance. Furthermore, the potential use of molecular biomarkers to predict sperm cryotolerance is discussed, as well as the addition of substances that can mitigate the harmful impact of freezing and thawing on sperm.

Effect of Dimethylacetamide Concentration on Motility, Quality, Antioxidant Biomarkers, Anti-Freeze Gene Expression, and Fertilizing Ability of Frozen/Thawed Rooster Sperm

Sperm cryopreservation is of great importance for the poultry industry but still needs to be optimized. The high susceptibility of poultry sperm to cryodamage leads to low fertility rates after cryopreservation. Therefore, the present study aimed at evaluating the effect of including a cryoprotectant, dimethylacetamide (DMA), in the chicken semen freezing extenders at a final concentration of 3%, 6%, or 9% on the post-thawed sperm motility, quality, antioxidant biomarkers, anti-freeze gene expression, and fertilizing ability. Results showed that the total motile sperm, progressivity, and viability were quadratically increased (p < 0.05) in the 6% DMA group. The antioxidant enzyme activity and lipid peroxidation were negatively (p < 0.05) affected by the increase in DMA concentration. Furthermore, some anti-freeze-associated genes such as heat shock protein 70 (HSP70) and ras homolog family member A (RHOA) were linearly and quadratically down-regulated (p < 0.05) with the high concentration of DMA. Finally, the fertility and hatchability rates did not indicate statistical differences between DMA groups. It can be concluded that using the low concentration of 3−6% DMA in the freezing semen extender is preferable to obtain acceptable results in the post-thawed sperm quality and fertility.

Effect of Sperm Cryopreservation in Farm Animals Using Nanotechnology

Sperm cryopreservation is one of the sublime biotechnologies for assisted reproduction. In recent decades, there has been an increasing trend in the use of preserved semen. Post-thaw semen quality and values vary among animals of the same species. Similarly, there are species-specific variations in sperm morphology, i.e., sperm head, kinetic properties, plasma membrane integrity, and freezability. Similarly, the viability of sperm varies in the female reproductive tract, i.e., from a few hours (in cattle) to several days (in chicken). Various steps of sperm cryopreservation, i.e., male health examination, semen collection, dilution, semen centrifugation, pre- and post-thaw semen quality evaluation, lack standardized methodology, that result in differences in opinions. Assisted reproductive technologies (ART), including sperm preservation, are not applied to the same extent in commercial poultry species as in mammalian species for management and economic reasons. Sperm preservation requires a reduction in physiological metabolism by extending the viable duration of the gametes. Physiologically and morphologically, spermatozoa are unique in structure and function to deliver paternal DNA and activate oocytes after fertilization. Variations in semen and sperm composition account for better handling of semen, which can aid in improved fertility. This review aims to provide an update on sperm cryopreservation in farm animals.

An Exploration of Current and Perspective Semen Analysis and Sperm Selection for Livestock Artificial Insemination

Artificial insemination of livestock has been a staple technology for producers worldwide for over sixty years. This reproductive technology has allowed for the rapid improvement of livestock genetics, most notably in dairy cattle and pigs. This field has experienced continuous improvements over the last six decades. Though much work has been carried out to improve the efficiency of AI, there are still many areas which continue to experience improvement, including semen analysis procedures, sperm selection techniques, sperm sexing technologies, and semen storage methods. Additionally, the use of AI continues to grow in beef cattle, horses, and small ruminants as the technology continues to become more efficient and yield higher pregnancy rates. In this review, AI trends in the various livestock species as well as cutting edge improvements in the aforementioned areas will be discussed at length. Future work will continue to refine the protocols which are used for AI and continue to increase pregnancy rates within all livestock species.

Opportunities and Limitations for Reproductive Science in Species Conservation

Reproductive science in the context of conservation biology is often understood solely in terms of breeding threatened species. Although technologies developed primarily for agriculture or biomedicine have a potentially important role in species conservation, their effectiveness is limited if we regard the main objective of animal conservation as helping to support populations rather than to breed a small number of individuals. The global threats facing wild species include the consequences of climate change, population growth, urbanization, atmospheric and water pollution, and the release of chemicals into the environment, to cite but a few. Reproductive sciences provide important and often unexpected windows into many of these consequences, and our aim here is both to demonstrate the breadth of reproductive science and the importance of basic knowledge and to suggest where some of the insights might be useful in mitigating the problems. 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.

Sperm migration, selection, survival, and fertilizing ability in the mammalian oviduct†

In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival, and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction that selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation, and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.

Sperm interactions with the female reproductive tract: A key for successful fertilization in mammals

Sperm migration through the female genital tract is not a quiet journey. Uterine contractions quickly operate a drastic selection, leading to a very restrictive number of sperm reaching the top of uterine horns and finally, provided the presence of key molecules on sperm, the oviduct, where fertilization takes place. During hours and sometimes days before fertilization, subpopulations of spermatozoa interact with dynamic and region-specific maternal components, including soluble proteins, extracellular vesicles and epithelial cells lining the lumen of the female tract. Interactions with uterine and oviductal cells play important roles for sperm survival as they modulate the maternal immune response and allow a transient storage before ovulation. The body of work reported here highlights the importance of sperm interactions with proteins originated from both the uterine and oviductal fluids, as well as hormonal signals around the time of ovulation for sperm acquisition of fertilizing competence.

ProAKAP4 as Novel Molecular Marker of Sperm Quality in Ram: An Integrative Study in Fresh, Cooled and Cryopreserved Sperm

To improve artificial insemination protocols in ovine species it is crucial to optimize sperm quality evaluation after preservation technologies. Emerging technologies based on novel biomolecules and related to redox balance and proteins involved in sperm motility such as ProAKAP4 could be successfully applied in ram sperm evaluation. In this work, a multiparametric analysis of fresh, cooled, and cryopreserved ram sperm was performed at different complexity levels. Samples were evaluated in terms of motility (total motility, progressive motility, and curvilinear velocity), viability, apoptosis, content of reactive oxygen species, oxidation‒reduction potential, and ProAKAP4 expression and concentration. As expected, cryopreserved samples showed a significant decrease of sperm quality (p < 0.05), evidencing different freezability classes among samples that were detected by ProAKAP4 analyses. However, in cooled sperm no differences were found concerning motility, viability, apoptosis, ROS content, and redox balance compared to fresh sperm that could explain the reported decrease in fertility rates. However, although the proportion of sperm ProAKAP4 positive-cells remained unaltered in cooled sperm compared to fresh control, the concentration of this protein significantly decreased (p < 0.05) in cooled samples. This altered protein level could contribute to the decrease in fertility rates of cooled samples detected by some authors. More importantly, ProAKAP4 can be established as a promising diagnostic parameter of sperm quality allowing us to optimize sperm conservation protocols and finally improve artificial insemination in ovine species.

Quantitative proteomic strategies to study reproduction in farm animals: Female reproductive fluids

Reproductive fluids from the female reproductive tract are gaining attention for their potential to support and optimize reproductive processes, including gamete maturation and embryo culture in vitro. Quantitative proteomics is a powerful way to decipher the proteome of reproductive tract fluids and to identify biologically relevant proteins. The present review describes proteomic strategies for analysing female reproductive fluid proteins. In addition, it considers the strategies for the preparation of oviductal, uterine and follicular fluid samples. Finally, it highlights the main results of quantitative proteomic studies, providing insights into the biological processes related to reproductive biology in farm animals. SIGNIFICANCE: Assisted reproductive technologies (ARTs) have become vitally important for farm animal breeding and much effort is going into the optimization and refinement of the techniques. There are also attempts to imitate physiological conditions by adding reproductive fluids or individual fluid proteins to improve in vitro procedures. A detailed knowledge of the reproductive fluid proteomes is indispensable. The present review summarizes the most widely used quantitative proteomic approaches for the analysis of fluids from the female reproductive tract and highlights the potential of quantitative proteomics to delineate reproductive processes and identify candidate proteins for ARTs in farm animals.

Oviductal Extracellular Vesicles Improve Post-Thaw Sperm Function in Red Wolves and Cheetahs

Artificial insemination (AI) is a valuable tool for ex situ wildlife conservation, allowing the re-infusion and dissemination of genetic material, even after death of the donor. However, the application of AI to species conservation is still limited, due mainly to the poor survival of cryopreserved sperm. Recent work demonstrated that oviductal extracellular vesicles (oEVs) improved cat sperm motility and reduced premature acrosomal exocytosis. Here, we build on these findings by describing the protein content of dog and cat oEVs and investigating whether the incubation of cryopreserved red wolf and cheetah sperm with oEVs during thawing improves sperm function. Both red wolf and cheetah sperm thawed with dog and cat oEVs, respectively, had more intact acrosomes than the non-EV controls. Moreover, red wolf sperm thawed in the presence of dog oEVs better maintained sperm motility over time (>15%) though such an improvement was not observed in cheetah sperm. Our work demonstrates that dog and cat oEVs carry proteins important for sperm function and improve post-thaw motility and/or acrosome integrity of red wolf and cheetah sperm in vitro. The findings show how oEVs can be a valuable tool for improving the success of AI with cryopreserved sperm in threatened species.

Comparative transcriptome analysis digs out genes related to antifreeze between fresh and frozen-thawed rooster sperm

The objective of this study was to investigate differences in mRNA expression between fresh and frozen–thawed sperm in roosters. In trial 1, gene expression profiles were measured using microarray with Affymetrix GeneChip Chicken Genome Arrays. The results showed that 2,115 genes were differentially expressed between the 2 groups. Among these genes, 2,086 were significantly downregulated and 29 were significantly upregulated in the frozen–thawed sperm group. Gene Ontology (GO) analysis showed that more than 1,000 differentially expressed genes (DEG) of all significantly regulated genes were involved in GO terms including biological processes, molecular function, and cellular component. Kyoto Encyclopedia of Genes and Genomes analysis showed that DEG were significantly (P < 0.05) enriched on ribosome, oxidative phosphorylation, proteasome, cell cycle, oocyte meiosis, and spliceosome pathways. In trial 2, ejaculated semen was collected from 18 roosters and divided into 5 recombinant HSP90 protein–supplemented groups (0.01, 0.1, 0.5, 1, or 2 μg/mL) and one control group with no recombinant HSP90 protein supplementation to evaluate the effect of recombinant HSP90 protein in the extender on post-thaw quality of rooster semen. The results showed that post-thaw sperm viability and motility was significantly improved (P < 0.05) in the extender containing 0.5 and 1 μg/mL of recombinant HSP90 protein compared with the control. Our preliminary results will provide a valuable basis for understanding the potential molecular mechanisms of cryodamage in frozen–thawed sperm and theoretical guidance to improve the fertility of frozen–thawed chicken sperm.

Adverse effects of in vitro manipulation of spermatozoa

Development of in vitro reproduction techniques has not only offered some infertile couples the possibility to have a child, it also revolutionized animal reproduction. Although in vitro reproduction techniques for humans or domestic and non-domestic animals have been designed to mimic in vivo conditions, modifications due to environmental effects or in vitro manipulation of gametes and embryos are unavoidable. For male gametes, in vitro manipulations include techniques to select spermatozoa, cryopreservation and other incubation procedures, during which spermatozoa may be exposed to oxidative stress and other insults that may damage their functions and DNA. The aim of this review is to provide an overview of key studies reporting sperm damage during in vitro manipulation, with particular focus on effects on DNA integrity, a fundamental factor for fertilization and transmission of paternal genetic information to offspring.

Advances in Cryopreservation of Bull Sperm

Cryopreservation of semen and artificial insemination have an important, positive impact on cattle production, and product quality. Through the use of cryopreserved semen and artificial insemination, sperm from the best breeding bulls can be used to inseminate thousands of cows around the world. Although cryopreservation of bull sperm has advanced beyond that of other species, there are still major gaps in the knowledge and technology bases. Post-thaw viability of sperm is still low and differs significantly among the breeding bulls. These weaknesses are important because they are preventing advances both in fundamental science of mammalian gametes and reproductive biotechnology. Various extenders have been developed and supplemented with chemicals to reduce cryodamage or oxidative stress with varying levels of success. More detailed insights on sperm morphology and function have been uncovered through application of advanced tools in modern molecular and cell biology. This article provides a concise review of progress in the cryopreservation of bull sperm, advances in extender development, and frontiers using diverse techniques of the study of sperm viability. This scientific resource is important in animal biotechnology because with the advances in discovery of sperm fertility markers, there is an urgent need to improve post-thaw viability and fertility of sperm through enhanced cryopreservation for precision agriculture to produce food animals to ensure food security on the global scale.

Identification of oxidatively modified proteins due to cryopreservation of carp semen

During semen cryopreservation, spermatozoa are exposed to physical and chemical stressors that result in their functional and structural damage. Growing evidence suggests that most cryoinjuries result from oxidative stress accompanying sperm cryopreservation. Elevated amounts of reactive oxygen species (ROS) generated during cryopreservation can react with sperm macromolecules, including proteins. The goal of this study was to investigate the oxidative modifications (measured as carbonylation level changes) of carp spermatozoa proteins triggered by the cryopreservation process. Flow cytometry and computer-assisted sperm analysis were used to evaluate changes in viability, ROS level, and motility of spermatozoa. The spermatozoa proteins that were specifically carbonylated were identified and quantified by Western blotting, in conjunction with 2-dimensional electrophoresis (2D-oxyblot) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry. Cryopreservation decreased spermatozoa motility (P < 0.01) and viability (P < 0.0001) and significantly increased (P < 0.0001) the number of ROS-positive cells. We identified 25 protein spots, corresponding to 19 proteins, with increases (P < 0.05) in carbonylation level due to freezing/thawing. The identified proteins are involved in motility, metabolism, calcium-ion binding, signal transduction, protein folding, and intracellular transport. The results suggest that carbonylation of flagellar proteins can result in motility disorders and may contribute to the reduced percentage of motile spermatozoa and disturbances in movement trajectory after sperm cryopreservation. Moreover, cryopreservation may contribute to impaired cellular respiration, ATP regeneration, disturbances of Ca2+ turnover, unfolding of cytoplasmic or histone proteins, disturbances of cell signaling and intracellular transport, and reduced membrane stability. Our results contribute to the knowledge concerning cryoinjury and to further development of a modified cryopreservation procedure aimed at minimizing oxidative damage of carp sperm proteins.

Review: The epic journey of sperm through the female reproductive tract

Millions or billions of sperm are deposited by artificial insemination or natural mating into the cow reproductive tract but only a few arrive at the site of fertilization and only one fertilizes an oocyte. The remarkable journey that successful sperm take to reach an oocyte is long and tortuous, and includes movement through viscous fluid, avoiding dead ends and hostile immune cells. The privileged collection of sperm that complete this journey must pass selection steps in the vagina, cervix, uterus, utero-tubal junction and oviduct. In many locations in the female reproductive tract, sperm interact with the epithelium and the luminal fluid, which can affect sperm motility and function. Sperm must also be tolerated by the immune system of the female for an adequate time to allow fertilization to occur. This review emphasizes literature about cattle but also includes work in other species that emphasizes critical broad concepts. Although all parts of the female reproductive tract are reviewed, particular attention is given to the sperm destination, the oviduct.

Identification of protein changes in human spermatozoa throughout the cryopreservation process

Cryoinjury is a consequence of cryopreservation and may have a negative impact on sperm quality regarding motility, morphology, and viability. This study was designed to identify potential proteomic changes in human sperm cells throughout the cryopreservation process. Comparisons made within this study included the detection of the sperm proteomic changes induced by incubation of the sperm cells with a protein-free cryoprotectant (with and without CryoSperm), and the proteomic changes induced by freezing, thawing, and subsequent after-thawing incubation at two different temperatures (0 °C vs. 23 °C). Tandem Mass Tag (TMT) peptide labeling coupled with LC-MS/MS was used for protein quantification. LC-MS/MS resulted in the identification of 769 quantifiable proteins. The abundance of 105 proteins was altered upon CryoSperm incubation. Freezing and thawing also induced substantial protein changes. However, fewer changes were observed when semen was thawed and then maintained after-thawing at approximately 0 °C than when it was maintained after-thawing at 23 °C, with 60 and 99 differential proteins detected, respectively, as compared to unfrozen semen incubated in CryoSperm. Collectively, these differences indicate that substantial changes occur in the sperm proteome at every stage of the cryopreservation process which may ultimately impair the sperm fertilizing capability. This is the first study to compare protein levels in fresh and cryopreserved semen using the TMT technology coupled to LC-MS/MS.

Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs

Cryopreservation is the most efficient method for long-term preservation of mammalian sperm. However, freeze-thawing procedures may strongly impair the sperm function and survival and thus decrease the reproductive performance. In addition, the sperm resilience to withstand cryopreservation, also known as freezability, presents a high individual variability. The present work summarizes the principles of cryoinjury and the relevance of permeating and nonpermeating cryoprotective agents. Descriptions about sperm cryodamage are mainly focused on boar sperm, but reference to other mammalian species is also made when relevant. Main cryoinjuries not only regard to sperm motility and membrane integrity, but also to the degradation effect exerted by freeze-thawing on other important components for sperm fertilizing ability, such as mRNAs. After delving into the main differences between good and poor freezability boar ejaculates, those protein markers predicting the sperm ability to sustain cryopreservation are also mentioned. Moreover, factors that may influence sperm freezability, such as season, diet, breed, or ejaculate fractions are discussed, together with the effects of different additives, like seminal plasma and antioxidants. After briefly referring to the effects of long-term sperm preservation in frozen state and the reproductive performance of frozen-thawed boar sperm, this work speculates with new research horizons on the preservation of boar sperm, such as vitrification and freeze-drying.