Statistical Series: Opportunities and challenges of sperm motility subpopulation analysis

Effect of Supplementation of a Cryopreservation Extender with Pectoliv30 on Post-Thawing Semen Quality Parameters in Rooster Species

Sperm cryopreservation is a fundamental tool for the conservation of avian genetic resources; however, avian spermatozoa are susceptible to this process. To cope with the high production of reactive oxygen species (ROS), the addition of exogenous antioxidants is beneficial. Pectoliv30 is a substance derived from alperujo, and in this study, its effect was analyzed on seminal quality after its addition to the cryopreservation extender of roosters at different concentrations. For this purpose, 16 Utrerana breed roosters were used, and seminal collection was performed in six replicates, creating a pool for each working day with ejaculates of quality. After cryopreservation, one sample per treatment and replicate was thawed, and several seminal quality parameters were evaluated. Statistical analysis revealed numerous correlations between these variables, both positive and negative according to the correlation matrix obtained. Furthermore, the chi-squared automatic interaction detection (CHAID) decision tree (DT) reported significant differences in the hypo-osmotic swelling test (HOST) variable between groups. Moreover, results for this parameter were more desirable at high concentrations of Pectoliv30. The application of this substance extracted from the by-product alperujo as an antioxidant allows the improvement of the post-thawing seminal quality in roosters and facilitates optimization of the cryopreservation process as a way to improve the conservation programs of different endangered poultry breeds.

The contribution of different sperm parameters to better explain ram semen cryoresistance

In order to determine an effective procedure for explaining ram sperm cryoresistance and develop a new model for breeders classification, a retrospective study was conducted using sperm analysis data obtained over two consecutive years from a total of 82 sessions of ram semen cryopreservation. In each session, fresh ejaculates from eight males were collected via artificial vagina, pooled and frozen in liquid nitrogen vapors. After thawing, a total of 19,084 sperm tracks and 11,319 morphometric measurements were analysed. Clustering analyses were applied to establish motile and morphometric sperm subpopulations. Additionally, plasma and acrosome membrane integrity, as well mitochondrial activity using flow cytometry immediately after sperm thawing and following hypoosmotic shock test (HOST) was assessed. To develop a Ram Sperm Cryoresistance Index, Principal Component Analyses (PCA) using 22 variables were conducted. In the first PCA, the parameters that best explain cryoresistance include total motility (TM), motile subpopulation 2 (motSP2, which groups slow, very linear spermatozoa with low lateral head displacement), morphometric subpopulation 1 (morphSP1, grouping spermatozoa with the smallest head size and lowest shape values), sperm plasma membrane integrity immediately after thawing and following hypoosmotic shock test. These parameters collectively account for 77.34 % of the accumulated variance. To emphasize their importance, a second PCA was performed, revealing significant higher weighting coefficients for the quantity (TM) and quality (motSP2) of sperm movement after thawing, compared to the head size and shape of the thawed sperm (morphSP1). Furthermore, HOST Viability played a more decisive role than what was observed under isotonic conditions.

Clustering of spermatozoa examined through flow cytometry provides more information than the conventional assessment: a resilience to osmotic stress example

Context Conventional sperm quality tests may not be sufficient to predict the fertilising ability of a given ejaculate; thus, rapid, reliable and sensitive tests are necessary to measure sperm function. Aims This study sought to address whether a cluster analysis approach based on flow cytometry variables could provide more information about sperm function. Methods Spermatozoa were exposed to either isotonic (300mOsm/kg) or hypotonic (180mOsm/kg) media for 5 and 20min, and were then stained with SYBR14 and propidium iodide (PI). Based on flow cytometry dot plots, spermatozoa were classified as either viable (SYBR14+ /PI- ) or with different degrees of plasma membrane alteration (SYBR14+ /PI+ and SYBR14- /PI+ ). Moreover, individual values of electronic volume (EV), side scattering (SS), green (FL1) and red (FL3) fluorescence were recorded and used to classify sperm cells through cluster analysis. Two strategies of this approach were run. The first one was based on EV and the FL3/FL1 quotient, and the second was based on EV, SS and the FL3/FL1 quotient. Key results The two strategies led to the identification of more than three sperm populations. In the first strategy, EV did not differ between membrane-intact and membrane-damaged sperm, but it was significantly (P P P Conclusions Cluster analysis based on flow cytometry variables provides more information about sperm function than conventional assessment does. Implications Combining flow cytometry with cluster analysis is a more robust approach for sperm evaluation.

The impact of Origanum Vulgare essential oil supplementation on sperm motility and subpopulation alterations in bulls, dogs, and rabbits

Artificial insemination is a widely adopted method in livestock production for various reasons such as health security and genetic improvement. Although sperm motility is of paramount importance in this technique as it directly influences the sperm's ability to fertilize the oocyte. In previous research on human sperm, we observed that in vitro supplementation with Origanum Vulgare essential oil significantly improved sperm motility and antioxidant activities, all without negatively affecting the integrity of their DNA. Based on these promising results, we considered it crucial to explore the potential effects of supplementation with this essential oil on sperm of other species. In this study, we studied the effects of oregano essential oil supplementation on sperm motility of (bulls = 15) (dogs = 15) and (rabbits = 9) and the changes that in vitro incubation with this oil could induce on sub-motile sperm populations of different species. The results of the study showed that in vitro oregano essential oil supplementation had a significant impact on sperm motility in the three species studied. This improvement in sperm motility was accompanied by an increase in the proportion of subpopulations with high velocity and progressivity: an increase of (2.16%, 10% and 4.84%) for subpopulation 1, (6.50%, 5.5% and 3.17%) for subpopulation 4 in bulls, dogs and rabbits respectively. While the subpopulations representing low motile and non-progressive sperm have decreased. These results suggest that the use of oregano essential oil can be a beneficial approach to improve sperm motility in different species, which can have important implications for the success of artificial insemination.

Post-testicular sperm maturation in ancient holostean species

Fish speciation was accompanied by changes in the urogenital system anatomy. In evolutionarily modern Teleostei, male reproductive tracts are fully separated from the excretory system, while in evolutionarily ancient Chondrostei and Holostei, the excretory and reproductive tracts are not separated. Sturgeon post-testicular sperm maturation (PTSM) occurring as a result of sperm/urine mixing is phenomenologically well described, while, in holosteans, functional intimacy of seminal ducts with kidney ducts and the existence of PTSM still need to be addressed. In Lepisosteus platostomus (Holostei), sperm samples were collected from testes (TS), efferent ducts (EDS), and Wolffian ducts (WDS). While WDS was motile, no motility was found in TS and EDS. The existence of PTSM was checked by in vitro PTSM procedure. After TS and EDS incubation in seminal fluid from WDS, no more than 5% motile spermatozoa were observed in TS, whereas in EDS the motility percentage was up to 75%. Experimental dyeing of urogenital ducts in gars and sturgeons revealed some differences in the interconnection between sperm ducts and kidneys. It is concluded that post-testicular sperm maturation occurs in gars and suggests that infraclass Holostei occupies an intermediate evolutionary position between Teleostei and Chondrostei in the anatomical arrangement of the urogenital system.

Motility Subpopulations with Distinct Motility Characteristics Using Swim-Up-Selected Sperm Cells from Norwegian Red Bulls: Effects of Freezing-Thawing and Between-Bull Variation

Discrete subpopulations of motile sperm cells have been found for several species and are implicated to be important for sperm functionality. The aim of this present study was to examine the motile subpopulations in swim-up-selected bull spermatozoa and the relationship between subpopulations in fresh and frozen-thawed sperm cells. In experiment 1, swim-up (SWUP)-selected and non-selected (control) sperm cells were analyzed using a Computer-Assisted Sperm Analyzer (CASA). In experiment 2, the semen from nine bulls was cryopreserved and analyzed using CASA both before and after freezing and after incubation at physiological temperatures. The SWUP population had a higher proportion of total motility, progressivity, and velocity compared to the control (p < 0.05). Likewise, both incubation over time and cryopreservation affected motility and motility parameters (p < 0.05). The population of rapid progressive (RapidP) sperm cells dominated the SWUP fraction and was higher than in the control samples (p < 0.05). Furthermore, RapidP was also the main part of fresh semen, but decreased significantly over time during incubation and due to cryopreservation. In conclusion, RapidP was the main population in SWUP-selected spermatozoa and seems to be an important subpopulation contributing to the differences between treatments and in response to the freezing of sperm cells.

A new computational approach, based on images trajectories, to identify the subjacent heterogeneity of sperm to the effects of ketanserin

The identification of kinematic subpopulations is of paramount importance to understanding the biological nature of the sperm heterogeneity. Nowadays, the data of motility parameters obtained by a computer-assisted sperm analysis (CASA) system has been used as input to distinct algorithms to identify kinematic subpopulations. In contrast, the images of the trajectories were depicted only as examples of the patterns of motility in each subpopulation. Here, python code was written to reconstruct the images of trajectories, from their coordinates, then the images of trajectories were used as input to a machine learning clustering algorithm of classification, and the subpopulations were described statistically by the motility parameters. Finally, the images of trajectories in each subpopulation were displayed in a way we called Pollock plots. Semen samples of boar sperm were treated with distinct concentrations of ketanserin (an antagonist of the 5-HT2 receptor of serotonin) and untreated samples were used as a control. The motility of sperm in each sample was analyzed at 0 and 30 min of incubation. Six subpopulations were found. The subpopulation 2 presented the highest values of velocities at 0 or 30 min. After 30 min of incubation, the ketanserin increased the values of the curvilinear velocity at high concentrations, whereas the linearity and the straight velocity decreased. Our computational model permits better identification of the kinematic subpopulations than the traditional approach and provides insights onto the heterogeneity of the response to ketanserin; thus, it could significantly impact the research on the relationship between sperm heterogeneity-fertility.

Exposure to silver and titanium dioxide nanoparticles at supra-environmental concentrations decreased sperm motility and affected spermatozoa subpopulations in gilthead seabream, Sparus aurata

Marine pollution by nanoparticles (NPs) can be reprotoxic for fish and disturb successful reproduction of wild populations. In gilthead seabream (Sparus aurata), a mild effect on sperm motility was observed after exposure to high concentrations of silver NPs. Considering the great heterogeneity traits within a sperm sample, it is possible that NPs affect spermatozoa accordingly, modulating subpopulation profile. Thus, this work aimed to analyse NP effects in sperm motility in general and considering spermatozoa population structure, using a subpopulation approach. Seabream sperm samples from mature males were exposed for 1 h to increasing concentrations of titanium dioxide (1, 10, 100, 1000 and 10,000 μg L^-1) and silver (0.25, 25 and 250 μg L^-1) NPs, including Ag NP and Ag⁺, dissolved in a non-activating medium (0.9 % NaCl). Concentrations chosen include realistic (10-100 and 0.25 μg L^-1, respectively, for TiO₂ and Ag) and supra-environmental values. The mean particle diameter was determined as 19.34 ± 6.72 and 21.50 ± 8.27 nm in the stock suspension, respectively, for titanium dioxide and silver. After the ex vivo exposure, sperm motility parameters were determined using computer-assisted sperm analysis, and sperm subpopulations were later identified using a two-step cluster analysis. Results revealed a significant reduction in total motility after exposure to the 2 highest concentrations of titanium dioxide NPs, while curvilinear and straight-line velocities were not altered. Exposure to silver NPs (Ag NP and Ag⁺) lowered significantly total and progressive motilities at all concentrations, while curvilinear and straight-line velocities were significantly lower only at the highest concentration. Sperm subpopulations were also affected by the exposure to both titanium dioxide and silver NPs. In both cases, the highest levels of NPs triggered a decrease in the percentage of fast sperm subpopulations (38.2% in TiO₂ 1000 μg L^-1, 34.8.% in Ag NP 250 μg L^-1, and 45.0% in Ag⁺ 250 μg L^-1 vs 53.4% in the control), while an increase on slow sperm subpopulations. A reprotoxic effect was proven for both NPs, but only at supra-environmental concentrations.

Are There Differences between Methods Used for the Objective Estimation of Boar Sperm Concentration and Motility?

Artificial insemination in the swine industry, as in other species, demands adequate semen handling and accurate evaluation for the preparation of seminal doses. Sperm concentration and motility estimates are part of the semen evaluation process and are considered important for maximizing the yield of doses for insemination. In this study, methods were examined for their accuracy in the estimation of boar sperm concentration and motility. Assessments of sperm concentration were carried out using iSperm^®, ISAS^® v1, Open CASA v2, and the Accuread^® photometer. Analyses of sperm motility were performed with iSperm^®, ISAS^® v1, and Open CASA v2 systems. In this study, boar semen samples were collected from 10 healthy males from two genetic lines. There were no relevant differences between sire lines when sperm concentration was assessed. A Bayesian analysis was applied to the four methods used to assess sperm concentration to examine whether there are relevant differences between them. Results suggested differences in the four methods, with a probability of relevance (PR) of 0.86-1.00. The iSperm^® method revealed higher concentration values within the highest posterior density region at 95% confidence interval (HPD_95%) = 167.0, 224.2 M/mL, whereas Open CASA v2 showed the lowest values, with HPD_95% = 99.3, 155.9 M/mL. The iSperm^® demonstrated higher reliability in measuring sperm concentration compared to other methods or devices within the given range of confidence. ANOVAs revealed relevant differences in the three methods of motility estimation. Overall, differences in boar sperm concentration and motility estimates were found using various methods, but further studies are needed for better characterization of these differences.

Assessment of sperm motility in livestock: Perspectives based on sperm swimming conditions in vivo

Evaluation of sperm motility is well-established in farm animals for quickly selecting ejaculates for semen processing into insemination doses and for evaluating the quality of preserved semen. Likewise, sperm motility is a fundamental parameter used by spermatologists in basic and applied science. Motility is commonly assessed using computer-assisted semen analysis (CASA). Recent increases in computational power, as well as utilization of mobile CASA systems and open-source CASA programs, broaden the possibilities for motility evaluation. Despite this technological progress, the potential of computer-generated motility data to assess male fertility remains challenging and may be limited. Relevance for fertility assessment could be improved if measurement conditions would more closely mimic the in vivo situation. Hence, this review is focused on the current trends of automated semen assessment in livestock and explores perspectives for future use with respect to the physiological and physical conditions encountered by sperm in the female reproductive tract. Validation of current CASA systems with more complex, microfluidic-based devices mimicking the female reproductive tract environment could improve the value of sperm kinematic data for assessing the fertilizing capacity of semen samples, not only for application in livestock but also for use in conducting assisted reproduction techniques in other species.

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.

What is the importance of sperm subpopulations?

The study of sperm subpopulations spans three decades. The origin, meaning, and practical significance, however, are less clear. Current technology for assessing sperm morphology (CASA-Morph) and motility (CASA-Mot) has enabled the accurate evaluation of these features, and there are many options for data classification. Subpopulations could occur as a result of the stage of development of each spermatozoon in the subpopulation. Spermatogenesis might contribute to the production of these subpopulations. Insights from evolutionary biology and recent molecular research are indicative of the diversity among male gametes that could occur from unequal sharing of transcripts and other elements through cytoplasmic bridges between spermatids. Sperm cohorts exiting the gonads would contain different RNA and protein contents, affecting the spermatozoon physiology and associations with the surrounding environmental milieu. Subsequently, these differences could affect how spermatozoa interact with the environmental milieu (maturation, mixing with seminal plasma, and interacting with the environmental milieu, or female genital tract and female gamete). The emergence of sperm subpopulations as an outcome of evolution, related to the reproductive strategies of the species, genital tract structures, and copulatory and fertilization processes. This kind of approach in determining the importance of sperm subpopulations in fertilization capacity should have a practical impact for conducting reproductive technologies, inspiring and enabling new ways for the more efficient use of spermatozoa in the medical, animal breeding, and conservation fields. This manuscript is a contribution to the Special Issue in memory of Dr. Duane Garner.

An optimized centrifugation protocol for ram sperm ensuring high sample yield, quality and fertility

The optimization and implementation of artificial insemination (AI) in sheep is necessary to increase the livestock productivity through enhanced control of reproductive function. Sperm centrifugation is a common procedure in the ejaculate handling in AI and other assisted reproductive technologies (ART), as part of new methods of sperm analysis, selection or preservation. However, our research group previously established that this simple procedure might cause a large sperm loss and induce deleterious effects on the sperm function of the ovine species when high centrifugation forces are employed. To our knowledge, there are no studies on combined effect of extender and different centrifugal forces on ram sperm yield and quality. Furthermore, evidence of in vivo fertility rate using sperm obtained with various centrifugation forces is also lacking in this species. Thus, the objective of this work was to define the ideal conditions for ram semen centrifugation that will achieve the best quantity and quality sample to ensure unaffected fertilization ability of centrifuged ram sperm. The Experiment 1 evaluated the effect of the centrifugation procedure of two extenders (INRA 96 and Tyrode's) and two cooling protocols (Rapid and Slow Refrigeration -35 °C to 15 °C-) on sperm recovery rate and quality (motility and kinetic parameters, viability, apoptosis and mitochondrial activity). INRA 96 combined with Slow Refrigeration and Tyrode's at room temperature registered the highest sperm recovery and quality values (P ≤ 0.05). In Experiment 2, the influence of three centrifugal forces (600, 1200 and 6000×g for 10 min) was assessed immediately after centrifugation on the technical performance and sperm functionality in diluted samples with INRA 96 and Tyrode's at the conditions set out in Experiment 1. The lowest pellet weight (P ≤ 0.05) without harmful effect on sperm physiological status (P > 0.05) was achieved at 1200×g, since 6000×g induced sperm motility damage (P ≤ 0.05) with both extenders. Finally, to ensure the total safety of the centrifugation protocol, Experiment 3 tested in a combined in vitro and in vivo test the effect of these three centrifugal forces on ram sperm quality after dilution (INRA 96) and liquid storage (6-8 h at 15 °C). The damage produced by 6000×g on sperm motility (P ≤ 0.05) was maintained over time, coinciding with a lower fertility (P ≤ 0.05). In conclusion, ram sperm can be centrifuged in INRA 96 extender up to 1200×g for 10 min at 15 °C as secure values with high recovery rates and without detrimental effects on sperm quality and fertility.

Predicting fertility from sperm motility landscapes

Understanding the organisational principles of sperm motility has both evolutionary and applied impact. The emergence of computer aided systems in this field came with the promise of automated quantification and classification, potentially improving our understanding of the determinants of reproductive success. Yet, nowadays the relationship between sperm variability and fertility remains unclear. Here, we characterize pig sperm motility using t-SNE, an embedding method adequate to study behavioural variability. T-SNE reveals a hierarchical organization of sperm motility across ejaculates and individuals, enabling accurate fertility predictions by means of Bayesian logistic regression. Our results show that sperm motility features, like high-speed and straight-lined motion, correlate positively with fertility and are more relevant than other sources of variability. We propose the combined use of embedding methods with Bayesian inference frameworks in order to achieve a better understanding of the relationship between fertility and sperm motility in animals, including humans.

Dimension reduction methods on porcine sperm motility landscapes reveal heterogeneity and hierarchy in sperm movement behavior and show high-speed and straight-lined motion as predictive features of 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.

Recombinant TrxAFNIIx4His6 improves post-thaw motility of ram sperm measured by a sperm motility tracker software

The aim of the present study was to evaluate a freezing extender supplemented with recombinant TrxAFNIIx4His_6, a reported decapacitating factor. Semen samples were diluted in tris-egg yolk medium with 0, 1.5 µM and 3.0 µM of TrxAFNIIx4His₆. Computer-assisted sperm motility tracking and subpopulations evaluation showed that addition of TrxAFNIIx4His₆ improved post-thaw total and progressive motility at both concentrations evaluated. TrxAFNIIx4His₆ increased the sperm subpopulation with the highest progressiveness and great velocity and decreased the subpopulation of poorly motile and almost non-progressive sperm. Incorporation of TrxAFNIIx4His₆ to freezing extender shows potential for the development of cryoprotection media which may lead to improved fertility after artificial insemination.

Sperm subpopulations influence the pregnancy rates in cattle

This study aimed to study the characteristics and subpopulations of spermatozoa from bulls with low and high reproductive performance based on pregnancy rates. Based on historical records of pregnancy rate from four farms, 24 bulls were selected. Two groups were established, with low pregnancy rates (n = 12; LOW), including bulls that presented pregnancy rates <52.27% (33.33% to 51.81%); and a group with high pregnancy rates (n = 12; HIGH), with pregnancy rates >52.27% (52.27% to 69.64%), after fixed-time artificial insemination (FTAI). The thawed sperm straws were analysed to sperm kinetics, morphology, plasma membrane integrity and sperm subpopulations. The LOW group exhibited a higher proportion of static cells (p < .05). In contrast, the HIGH group showed greater percentages for membrane integrity and total and progressive motility, and cells with fast and medium velocity (p < .05). In the cluster procedures, four sperm subpopulations were established. The low-fertility bulls presented the highest percentage of subpopulation 2 (41.46%), characterized by slow and progressive spermatozoa. The high-fertility bulls exhibited the highest percentage of subpopulation 3 (37.17%), characterized by fast and nonlinear spermatozoa. Results from this study indicated that bulls with greater percentages of fast and nonlinear spermatozoa seem to have greater fertilization capacity and the subpopulations analysis can be considered a tool to identify ejaculates with high fertility.

Sperm kinematic subpopulations of the American crocodile (Crocodylus acutus)

There has been very limited use of computer assisted semen analysis (CASA) to evaluate reptile sperm. The aim of this study was to examine sperm kinematic variables in American crocodile (Crocodylus acutus) semen samples and to assess whether sperm subpopulations could be characterized. Eight ejaculates (two ejaculates/male) from four sexually mature captive crocodiles were obtained. An ISAS®v1 CASA-Mot system, with an image acquisition rate of 50 Hz, and ISAS®D4C20 counting chambers were used for sperm analyses. The percentages of motile and progressively motile spermatozoa did not differ among animals (P > 0.05) but there was a significant animal effect with regards to kinematic variables (P < 0.05). Principal component (PC) analysis revealed that kinematic variables grouped into three components: PC1, related to velocity; PC2 to progressiveness and PC3 to oscillation. Subpopulation structure analysis identified four groups (P < 0.05), which represented, on average, 9.8%, 32.1%, 26.8%, and 31.3% of the total sperm population. Males differed in the proportion of sperm in each of the kinematic subpopulations. This new approach for the analysis of reptile sperm kinematic subpopulations, reflecting quantifiable parameters generated by CASA system technology, opens up possibilities for future assessments of crocodile sperm and will be useful in the future development of assisted reproduction for these species.

The effects of cryopreservation and cold storage on sperm subpopulation structure of common carp (Cyprinus carpio L.)

The objectives of this study were to identify the presence of different spermatozoa subpopulations (SPs) according to their kinematic characteristics in the sperm of common carp and to test the effects of cryopreservation and prolonged (6-day) storage at room temperature (RT; 23 °C) and 4 °C on spermatozoa motility and subsequently on SP dynamics. Two-step clustering analyses identified three motile SPs based on their kinematic properties: SP1 contained spermatozoa with low velocity and low/moderate STR/LIN values (slow non-linear SP); SP2 was comprised of spermatozoa with high velocities and high STR/LIN values (fast linear SP); SP3 was characterized with high VCL, and moderate LIN/STR (fast non-linear SP); and an additional SP0 was added comprising immotile spermatozoa. Total motility, progressive motility and VCL decreased after cryopreservation to approximately 50% of their value in fresh sperm, while the frequency of SPs characterized by high values of motility parameters declined in favor of those with low motility values and SP0. Motility values of fresh and cryopreserved spermatozoa which were washed with fresh extender after thawing decreased significantly after 24 h of storage at RT and after 72 h of storage at 4 °C, while cryopreserved sperm which remained in the original cryomedium faced a steep decline in motility after only 2 h of storage. As subpopulation frequencies followed this dynamic, this indicates that cryopreserved sperm should be washed with fresh extender in order to obtain favorable sperm kinematic properties after freezing.

Collapsed mitochondrial cristae in goat spermatozoa due to mercury result in lethality and compromised motility along with altered kinematic patterns

Earlier we have reported mercury-induced alterations in functional dynamics of buck spermatozoa through free radicals-mediated oxidative stress and spontaneous acrosome reaction. Based on our earlier findings, we aimed to investigate the effect of mercury exposure on motility, kinematic patterns, DNA damage, apoptosis and ultra-structural alterations in goat spermatozoa following in vitro exposure to different concentrations (0.031-1.25 µg/ml) of mercuric chloride for 15 min and 3 h. Following exposure of sperm cells to 0.031 µg/ml of mercuric chloride for 3 h, livability and motility of sperms was significantly reduced along with altered kinematic patterns, significant increase in per cent necrotic sperm cells and number of cells showing DNA damage; and this effect was dose- and time-dependent. Contrary to up-regulation of Bax gene after 3 h in control group, there was significant increase in expression of Bcl-2 in mercury-treated groups. Transmission electron microscopy studies revealed rifts and nicks in plasma and acrosomal membrane, mitochondrial sheath, and collapsed mitochondria with loss of helical organization of mitochondria in the middle piece of spermatozoa. Our findings evidently suggest that mercury induces necrosis instead of apoptosis and targets the membrane, acrosome, mid piece of sperms; and the damage to mitochondria seems to be responsible for alterations in functional and kinematic attributes of spermatozoa.

Estimate of in vitro embryo production based on sperm subpopulations in Senepol bulls

In cattle, in vitro embryo production (IVEP) is an important reproductive biotechnology responsible for the rapid expansion of the Senepol breed in our country. This breed has shown important results when used in crossbreeding and estimate IVEP in Senepol based on seminal analysis would be valuable for the semen cryopreservation industry, research institutes and breeders. Combining the evaluation of sperm subpopulations with analysis of other sperm attributes may help to improve fertility predictions in cattle. Therefore, the objectives of the present study were to: 1) identify and characterize motile sperm subpopulations in cryopreserved Senepol semen following the washing process carried out before in vitro fertilization, and 2) to determine an model for estimate IVEP based on sperm subpopulations in conjunction with other sperm quality analyzes. Samples of 38 cryopreserved semen from 28 Senepol bulls, chosen based on retrospective data from 386 IVEP routines, underwent the semen washing and were evaluated by the computer-assisted sperm analysis system. Sperm morphology was evaluated by wet preparation technique, and plasma and acrosomal membranes integrity, mitochondrial potential, oxidative status and chromatin resistance were analyzed by flow cytometry. After multivariate analysis of principal components and grouping, three sperm subpopulations were identified: SBP1 (fast and progressive motility), SBP2 (hyperactivated motility) and SBP3 (slow non-progressive motility). After categorization of IVEP in high, medium and low embryo yield, logistic regression analysis was applied to associate the results of subpopulations and other sperm quality variables with IVEP. The SBP1 and SBP2 variables affected embryo production, and an IVEP estimation model was generated for Senepol bulls based on these two subpopulations: embryo yield = 0.1563 + 0.0328 (SBP1) + 0.0173 (SBP2). SBP1 and SBP2 represents the absolute value of the percentage of subpopulations in semen. If the calculated value (by this equation) is close to 1, the embryo yield will be low; if is close to 2, will be medium; if is close to 3, will be high. In conclusion, three subpopulations were found for Senepol semen and, despite all analyzed variables, only SBP1 and SBP2 were included in the model to estimate IVEP in this breed.

Effect of Seminal Plasma Protein Fractions on Stallion Sperm Cryopreservation

Seminal plasma (SP) is the natural environment for spermatozoa and contains a number of components, especially proteins important for successful sperm maturation and fertilization. Nevertheless, in standard frozen stallion insemination doses production, SP is completely removed and is replaced by a semen extender. In the present study, we analyzed the effects of the selected seminal plasma protein groups that might play an important role in reducing the detrimental effects on spermatozoa during the cryopreservation process. SP proteins were separated according to their ability to bind to heparin into heparin-binding (Hep+) and heparin-non-binding (Hep-) fractions. The addition of three concentrations-125, 250, and 500 µg/mL-of each protein fraction was tested. After thawing, the following parameters were assessed: sperm motility (by CASA), plasma membrane integrity (PI staining), and acrosomal membrane integrity (PNA staining) using flow cytometry, and capacitation status (anti-phosphotyrosine antibody) using imaging-based flow cytometry. Our results showed that SP protein fractions had a significant effect on the kinematic parameters of spermatozoa and on a proportion of their subpopulations. The 125 µg/mL of Hep+ protein fraction resulted in increased linearity (LIN) and straightness (STR), moreover, with the highest values of sperm velocities (VAP, VSL), also this group contained the highest proportion of the fast sperm subpopulation. In contrast, the highest percentage of slow subpopulation was in the groups with 500 µg/mL of Hep+ fraction and 250 µg/mL of Hep- fraction. Interestingly, acrosomal membrane integrity was also highest in the groups with Hep+ fraction in concentrations of 125 µg/mL. Our results showed that the addition of protein fractions did not significantly affect the plasma membrane integrity and capacitation status of stallion spermatozoa. Moreover, our results confirmed that the effect of SP proteins on the sperm functionality is concentration-dependent, as has been reported for other species. Our study significantly contributes to the lack of studies dealing with possible use of specific stallion SP fractions in the complex puzzle of the improvement of cryopreservation protocols. It is clear that improvement in this field still needs more outputs from future studies, which should be focused on the effect of individual SP proteins on other sperm functional parameters with further implication on the success of artificial insemination in in vivo conditions.

Kinematic Sub-Populations in Bull Spermatozoa: A Comparison of Classical and Bayesian Approaches

The ejaculate is heterogenous and sperm sub-populations with different kinematic patterns can be identified in various species. Nevertheless, although these sub-populations are statistically well defined, the statistical differences are not always relevant. The aim of the present study was to characterize kinematic sub-populations in sperm from two bovine species, and diluted with different commercial extenders, and to determine the statistical relevance of sub-populations through Bayesian analysis. Semen from 10 bulls was evaluated after thawing. An ISAS®v1 computer-assisted sperm analysis (CASA)-Mot system was employed with an image acquisition rate of 50 Hz and ISAS®D4C20 counting chambers. Sub-populations of motile spermatozoa were characterized using multivariate procedures such as principal components (PCs) analysis and clustering methods (k-means model). Four different sperm sub-populations were identified from three PCs that involved progressiveness, velocity, and cell undulatory movement. The proportions of the different sperm sub-populations varied with the extender used and in the two species. Despite a statistical difference (p < 0.05) between extenders, the Bayesian analysis confirmed that only one of them (Triladyl®) presented relevant differences in kinematic patterns when compared with Tris-EY and OptiXcell®. Extenders differed in the proportion of sperm cells in each of the kinematic sub-populations. Similar patterns were identified in Bos taurus and Bos indicus. Bayesian results indicate that sub-populations SP1, SP2, and SP3 were different for PC criteria and these differences were relevant. For velocity, linearity, and progressiveness, the SP4 did not show a relevant difference regarding the other sperm sub-populations. The classical approach of clustering or sperm subpopulation thus may not have a direct biological meaning. Therefore, the biological relevance of sperm sub-populations needs to be reevaluated.

Different approaches for assessing sperm function

Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the "one shot" parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways.

Melatonin Non-Linearly Modulates Bull Spermatozoa Motility and Physiology in Capacitating and Non-Capacitating Conditions

Bull spermatozoa physiology may be modulated by melatonin. We washed ejaculated spermatozoa free of melatonin and incubated them (4 h, 38 °C) with 0-pM, 1-pM, 100-pM, 10-nM and 1-µM melatonin in TALP-HEPES (non-capacitating) and TALP-HEPES-heparin (capacitating). This range of concentrations encompassed the effects mediated by melatonin receptors (pM), intracellular targets (nM–µM) or antioxidant activity (µM). Treatment effects were assessed as motility changes by computer-assisted sperm analysis (CASA) of motility and physiological changes by flow cytometry. Melatonin effects were more evident in capacitating conditions, with 100 pM reducing motility and velocity (VCL) while increasing a “slow” subpopulation. All concentrations decreased apoptotic spermatozoa and stimulated mitochondrial activity in viable spermatozoa, with 100 pM–1 µM increasing acrosomal damage, 10 nM–1 µM increasing intracellular calcium and 1 pM reducing the response to a calcium-ionophore challenge. In non-capacitating media, 1 µM increased hyperactivation-related variables and decreased apoptotic spermatozoa; 100 pM–1 µM increased membrane disorders (related to capacitation); all concentrations decreased mitochondrial ROS production. Melatonin concentrations had a modal effect on bull spermatozoa, suggesting a capacitation-modulating role and protective effect at physiological concentrations (pM). Some effects may be of practical use, considering artificial reproductive techniques.

Motile sperm subpopulations in bull semen using different clustering approaches - Associations with flow cytometric sperm characteristics and fertility

There are sperm subpopulations (SPs) with different kinematic characteristics in various species, however, biological relevance of these SPs is still uncertain. The objective of the present study was to investigate associations of motile sperm SPs with sperm characteristics determined by evaluations with flow cytometry and assessment of bull fertility, using multiple approaches for sperm clustering. Semen from 24 bulls was evaluated concomitantly using computer-assisted sperm analysis (CASA) and flow cytometry before freezing and after thawing. Motile SPs were determined utilizing two acknowledged clustering methods (TwoStep and K-Means) and one customized method. With the customized method, there was utilization of mean values of sperm velocity and linearity as thresholds for direct assignment of motile spermatozoa into four SPs. Regardless of approach for identifying SPs, sperm quality, as determined using flow cytometry, was correlated particularly with the subpopulation (SP) of fast and linear spermatozoa immediately after thawing and with the SP of fast and nonlinear spermatozoa before freezing and 3 h after thawing. Furthermore, there was a positive correlation between proportion of spermatozoa with fast and nonlinear movements before freezing and bull non-return to estrous rates. These results indicate that with different sperm SPs, there are different biological implications which can be evaluated to gain useful information concerning semen quality as determined using flow cytometry and fertility. Furthermore, determining SPs by assigning motile spermatozoa into clusters based on a combination of "below and "above" threshold values for sperm velocity and linearity might be considered a practical alternative to otherwise intricate clustering procedures.

Novel Techniques of Sperm Selection for Improving IVF and ICSI Outcomes

Almost 50% of the infertility cases are due to male factors. Assisted reproductive technologies (ARTs) allow to overcome the incapacity of these patients' spermatozoa to fertilize the oocyte and produce a viable and healthy offspring, but the efficiency of the different techniques has still the potential to improve. According to the latest reports of the European Society of Human Reproduction and Embryology (ESHRE) and the Centers for Disease Control and Prevention of the United States (CDC), the percentages of deliveries per ART cycle in 2014 and 2016 were 21 and 22%, respectively. Among the reasons for this relatively low efficiency, the quality of the spermatozoa has been pointed out as critical, and the presence of high percentages of DNA-damaged spermatozoa in patients' ejaculates is possibly one of the main factors reducing the ARTs outcomes. Thus, one of the main challenges in reproductive medicine is to ensure the highest quality of the spermatozoa used in ARTs, and specifically, in terms of genetic integrity. The latest techniques for the preparation and selection of human spermatozoa are herein discussed focusing on those proven to improve one or several of the following parameters: sperm genetic integrity, fertilization capacity, embryo production, and in vitro survival, as well as pregnancy and delivery rates following in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). In addition, we discuss the potential of techniques developed in non-human mammals that could be further transferred to the clinic.

Low Density Lipoprotein - important player in increasing cryoprotective efficiency of soybean lecithin-based bull semen extenders

Currently, considering cryopreservation of bull semen, there is no clear consensus over the comparability of cryoprotective efficacy of extenders with soybean lecithin and those based on egg yolk. The objective of this study was to prove the use of Low Density Lipoprotein (LDL) extracted from hen-egg yolk as an enhancing factor for soybean lecithin-based extenders. In total, 35 ejaculates of (seven bulls x five ejaculates per bull) were collected and cryopreserved at a commercial insemination centre. The effect of the LDL addition to the extenders AndroMed^® and Bioxcell^® was tested in a 6% (v/v) concentration on spermatozoa after thawing. Modified extender composition effects were assessed on sperm functional parameters motility, plasma membrane, mitochondrial membrane potential and acrosomal integrity after thawing by CASA, flow cytometry and fluorescent microscopy, respectively. Based on kinematic parameters determined from CASA, k-means cluster analysis was used to classify individual spermatozoon into specific subpopulations (fast, medium fast and slow). A subpopulation of fast spermatozoa was increased in the presence of LDL in both selected extenders (P < 0.05). Moreover, the positive effect of LDL on sperm motility was confirmed by decreasing the percentage of sperm in slow subpopulation (P < 0.05). The effect of LDL addition on the incidence of spermatozoa with intact plasma membrane was not demonstrated in any case of extender used (P > 0.05). The percentage of sperm with intact acrosome was improved when LDL was added to Bioxcell^® extender (P < 0.05). On the other hand, addition of LDL to AndroMed^® extender improved mitochondrial intactness after thawing (P < 0.05). In conclusion, our results showed that adding LDL to selected soybean lecithin-based extenders considerably ameliorated the functional parameters of spermatozoa after thawing and thus this lipoprotein could represent an improving agent for soybean lecithin-based extender for bull semen cryopreservation.

Effects of temperature on sperm motility of burbot Lota lota: spontaneous activation and calcium dependency

Several factors regulating activation of spermatozoon motility in Eurasian burbot, Lota lota, including osmolality, calcium (Ca²⁺ ) ions, and temperature were investigated. Spermatozoon motility in Eurasian burbot, Lota lota was assessed at 4 and 30°C in seminal fluid, isotonic media (with and without Ca²⁺ ) and hypotonic media (with and without Ca²⁺ ). Spermatozoa were spontaneously activated in seminal fluid at 20°C and the maximum motility was recorded at 30°C, which is out of the spawning temperature range, indicating that no risk of activation occurs during routine semen handling in artificial insemination. Initiation of spermatozoon motility in L. lota is mediated by Ca²⁺ and sensitivity to Ca²⁺ is dependent on temperature.

Making the most of sperm activation responses: experiments with boar spermatozoa and bicarbonate

Attempting to extract useful and reliable information about semen quality and its fertility potential remains a difficult exercise, partly because the sperm heterogeneity within samples often renders simple statistical analyses rather meaningless. In fact, a mean and standard deviation may reflect neither the very fast swimming activities of the most active cells nor the slow and sluggish activities of others. Herein we propose that the information value within semen samples can be maximised if current knowledge about sperm activation mechanisms is exploited before undertaking the measurements. We explain, using boar semen as an example, that estimating and defining relative sperm subpopulation sizes, after activation by bicarbonate, provides a means of quantifying sperm quality. Although such estimates may indeed be related to in vivo fertility, the general approach also suggests potential new avenues that could be exploited for the elaboration of novel in vitro tests for the characterisation of toxic environmental chemicals and, indeed, to reduce the number of animals used in such testing programs.

Implementation of novel statistical procedures and other advanced approaches to improve analysis of CASA data

Computer-aided sperm analysis (CASA) produces a wealth of data that is frequently ignored. The use of multiparametric statistical methods can help explore these datasets, unveiling the subpopulation structure of sperm samples. In this review we analyse the significance of the internal heterogeneity of sperm samples and its relevance. We also provide a brief description of the statistical tools used for extracting sperm subpopulations from the datasets, namely unsupervised clustering (with non-hierarchical, hierarchical and two-step methods) and the most advanced supervised methods, based on machine learning. The former method has allowed exploration of subpopulation patterns in many species, whereas the latter offering further possibilities, especially considering functional studies and the practical use of subpopulation analysis. We also consider novel approaches, such as the use of geometric morphometrics or imaging flow cytometry. Finally, although the data provided by CASA systems provides valuable information on sperm samples by applying clustering analyses, there are several caveats. Protocols for capturing and analysing motility or morphometry should be standardised and adapted to each experiment, and the algorithms should be open in order to allow comparison of results between laboratories. Moreover, we must be aware of new technology that could change the paradigm for studying sperm motility and morphology.

Current perspectives of CASA applications in diverse mammalian spermatozoa

Since the advent of computer-aided sperm analysis (CASA) some four decades ago, advances in computer technology and software algorithms have helped establish it as a research and diagnostic instrument for the analysis of spermatozoa. Despite mammalian spermatozoa being the most diverse cell type known, CASA is a great tool that has the capacity to provide rapid, reliable and objective quantitative assessment of sperm quality. This paper provides contemporary research findings illustrating the scientific and commercial applications of CASA and its ability to evaluate diverse mammalian spermatozoa (human, primates, rodents, domestic mammals, wildlife species) at both structural and functional levels. The potential of CASA to quantitatively measure essential aspects related to sperm subpopulations, hyperactivation, morphology and morphometry is also demonstrated. Furthermore, applications of CASA are provided for improved mammalian sperm quality assessment, evaluation of sperm functionality and the effect of different chemical substances or pathologies on sperm fertilising ability. It is clear that CASA has evolved significantly and is currently superior to many manual techniques in the research and clinical setting.

An update on boar semen assessments by flow cytometry and CASA

In the quest for predicting fertility of an individual, enhancing semen handling, dilution and storage protocols, and understanding the impact of environment and, andrologists have changed their approaches to semen analysis. The technologies used today are fast developing and readily implemented in research. Semen is one of a few naturally occurring monocellular suspensions, so sperm function analysis by flow cytometry (FC) and utilization of fluorochromes is an ideal technique for high throughput, objective and accurate analysis. The complementary use of microscopical assessments by Computer-Assisted Semen Analysis (CASA), where sperm cell parameters can be objectively assessed is equally important. The objectivity and repeatability of these techniques have driven research on the function, identification of heterogeneity and fertility of the ejaculate. The wealth of knowledge obtained from the application of these powerful methods has changed our view of the spermatozoon. Although there is some application of these methods in the industry producing boar semen for artificial insemination (AI) and to eliminate sires of sub-standard semen quality, uptake of advanced methods is still slow. Instruments are becoming cheaper and technically more user friendly. Standardization of methodology and optimization of instrument settings is important for full implementation of these systems, including comparison between labs. This review provides an update on two technologies: flow cytometry and CASA for objective analysis of boar semen quality.

Positive effect of butylated hydroxytoluene (BHT) on the quality of cryopreserved cat spermatozoa

The semen cryopreservation processes are associated with state of oxidative stress induced by high levels of reactive oxygen species (ROS), causing damage to functional spermatozoa. Whereby, antioxidants have been utilized to scavenge or neutralize the elevated levels of ROS. The aim of at the present study was to evaluate the effect of adding BHT to the freezing extenders on post-thaw characteristics of domestic cat spermatozoa. Semen samples were frozen in Tris-fructose-citric acid-based extender, supplemented with different concentrations of BHT (0.5 mM, 1.0 mM and 2.0 mM) and a control sample without antioxidant. After thawing, sperm samples were assessed for motility by computer-assisted sperm analysis and viability, acrosome integrity, superoxide anion production and membrane lipid peroxidation status by flow cytometry. In the study, the parameters of sperm motility and acrosome integrity were significantly higher in 2.0 mM BHT compared to sperm frozen in the extender with other concentrations and control (P < 0.05), in addition, this concentration reduced significantly the superoxide anion production and lipid peroxidation of the sperm. The results demonstrated that the supplementation of BHT to the freezing extender could protect the function and cellular structure of domestic cat sperm from cryoinjuries.

High-throughput characterisation of bull semen motility using differential dynamic microscopy

We report a high-throughput technique for characterising the motility of spermatozoa using differential dynamic microscopy. A movie with large field of view (∼10mm2) records thousands of cells (e.g. ≈ 5000 cells even at a low cell density of 20 × 106 cells/ml) at once and yields averaged measurements of the mean ([Formula: see text]) and standard deviation (σ) of the swimming speed, head oscillation amplitude (A0) and frequency (f0), and the fraction of motile spermatozoa (α). Interestingly, we found that the measurement of α is facilitated because the swimming spermatozoa enhance the motion of the non-swimming population. We demonstrate the ease and rapidity of our method by performing on-farm characterisation of bull spermatozoa motility, and validate the technique by comparing laboratory measurements with tracking. Our results confirm the long-standing theoretical prediction that [Formula: see text] for swimming spermatozoa.

Thawing boar semen in the presence of seminal plasma improves motility, modifies subpopulation patterns and reduces chromatin alterations

Seminal plasma could have positive effects on boar semen after thawing. In the present study we investigated changes in the motility and chromatin structure in spermatozoa over 4h incubation (37°C) of boar semen thawed in the presence of 0%, 10% or 50% seminal plasma from good-fertility boars. Cryopreserved doses were used from seven males, three of which were identified as susceptible to post-thawing chromatin alterations. Motility was analysed by computer-aided sperm analysis every hour, and data were used in a two-step clustering, yielding three subpopulations of spermatozoa (slow non-linear, fast non-linear, fast linear). Chromatin structure was analysed using a sperm chromatin structure assay and flow cytometry to determine the DNA fragmentation index (%DFI) as a percentage, the standard deviation of the DFI (SD-DFI) and the percentage of high DNA stainability (%HDS), indicating chromatin compaction. Thawing without seminal plasma resulted in a rapid loss of motility, whereas seminal plasma helped maintain motility throughout the incubation period and preserved the subpopulation comprising fast and linear spermatozoa. The incidence of chromatin alterations was very low in samples from non-susceptible males, whereas samples from males susceptible to post-thawing chromatin alterations exhibited marked alterations in%DFI and%HDS. Seminal plasma partly prevented these alterations in samples from susceptible males. Overall, 50% seminal plasma was the most efficient concentration to protect motility and chromatin. Some changes were concomitant with physiological events reported previously (e.g., semen thawed with 50% seminal plasma increased the production of reactive oxygen species and yielded higher fertility after AI). Thawing in the presence of seminal plasma could be particularly useful in the case of samples susceptible to post-thawing chromatin damage.

Boar sperm hyperactivated motility is induced by temperature via an intracellular calcium-dependent pathway

Herein we describe a new protocol to induce boar sperm hypermotility: temperature-induced hypermotility (TIH). Briefly, spermatozoa stored at 17°C in a calcium-free Tyrode’s basal medium (containing EGTA) were exposed to increased temperature by incubation at 38.5°C. Hypermotility induced by the calcium ionophore A23187 was used as a control (calcium ionophore-induced hyperactivity (CIIH)). The increase in temperature led to an increase in the percentage of hypermotile spermatozoa. When the slope of the temperature increase is near zero, sperm hyperactivity becomes a more progressive movement. Motility parameters of sperm hyperactivation induced by TIH were different from those following CIIH. Cluster analysis revealed that these two populations of hyperactivated spermatozoa are different. TIH is independent of extracellular Ca2+ but dependent on intracellular Ca2+ release. Moreover, TIH is unaffected by protein kinase A (PKA) inhibition, whereas CIIH is reduced by half in the presence of a PKA inhibitor. In conclusion, we have demonstrated that: (1) a temperature increase in boar spermatozoa is a stimulus that can induce a hyperactive population, which is differs from the hyperactive sperm population induced by calcium ionophore; (2) the temperature increase in spermatozoa triggers the release of Ca2+ from intracellular stores; (3) extracellular calcium is not required for TIH; and (4) TIH in boar spermatozoa is independent of PKA activity.

Comparison of sperm motility subpopulation structure among wild anadromous and farmed male Atlantic salmon (Salmo salar) parr using a CASA system

Atlantic salmon (Salmo salar) is an endangered freshwater species that needs help to recover its wild stocks. However, the priority in aquaculture is to obtain successful fertilisation and genetic variability to secure the revival of the species. The aims of the present work were to study sperm subpopulation structure and motility patterns in wild anadromous males and farmed male Atlantic salmon parr. Salmon sperm samples were collected from wild anadromous salmon (WS) and two generations of farmed parr males. Sperm samples were collected from sexually mature males and sperm motility was analysed at different times after activation (5 and 35 s). Differences among the three groups were analysed using statistical techniques based on Cluster analysis the Bayesian method. Atlantic salmon were found to have three sperm subpopulations, and the spermatozoa in ejaculates of mature farmed parr males had a higher velocity and larger size than those of WS males. This could be an adaptation to high sperm competition because salmonid species are naturally adapted to this process. Motility analysis enables us to identify sperm subpopulations, and it may be useful to correlate these sperm subpopulations with fertilisation ability to test whether faster-swimming spermatozoa have a higher probability of success.

Cluster analysis reveals seasonal variation of sperm subpopulations in extended boar semen

This study aimed to identify motile sperm subpopulations in extended boar semen and to observe the presumptive seasonal variation in their distribution. Data from 4837 boar ejaculates collected over a two-year period were analyzed in terms of kinematic parameters by Computer Assisted Sperm Analysis (CASA). Individual sperm data were used to determine subgroups of motile sperm within the ejaculates using cluster analysis. Four motile sperm subpopulations (SP) were identified, with distinct movement patterns: SP1 sperm with high velocity and high linearity; SP2 sperm with high velocity but low linearity; SP3 sperm with low velocity but high linearity; and SP4 sperm with low velocity and low linearity. SP1 constituted the least overall proportion within the ejaculates (P < 0.05). Season of semen collection significantly influenced the different proportions of sperm subpopulations. Spring was characterized by similar proportions of SP1 and SP4 (NS) and higher proportions of SP3. Summer brought a decrease in both subgroups containing fast sperm (SP1 and SP2) (P < 0.05). During autumn, increases in SP2 and SP4 were recorded. Winter substantially affected the proportions of all sperm subpopulations (P < 0.05) and SP2 became the most represented subgroup, while SP1 (fast and linear) reached its highest proportion compared to other seasons. In conclusion, extended boar semen is structured in distinct motile sperm subpopulations whose proportions vary according to the season of collection. Summer and autumn seem to have a negative impact on the fast and linear subpopulation. Cluster analysis can be useful in revealing differences in semen quality that are not normally detected by classical evaluation based on mean values.

Effect of sexual steroids on boar kinematic sperm subpopulations

Here, we show the effects of sexual steroids, progesterone, testosterone, or estradiol on motility parameters of boar sperm. Sixteen commercial seminal doses, four each of four adult boars, were analyzed using computer assisted sperm analysis (CASA). Mean values of motility parameters were analyzed by bivariate and multivariate statistics. Principal component analysis (PCA), followed by hierarchical clustering, was applied on data of motility parameters, provided automatically as intervals by the CASA system. Effects of sexual steroids were described in the kinematic subpopulations identified from multivariate statistics. Mean values of motility parameters were not significantly changed after addition of sexual steroids. Multivariate graphics showed that sperm subpopulations were not sensitive to the addition of either testosterone or estradiol, but sperm subpopulations responsive to progesterone were found. Distribution of motility parameters were wide in controls but sharpened at distinct concentrations of progesterone. We conclude that kinematic sperm subpopulations responsive to progesterone are present in boar semen, and these subpopulations are masked in evaluations of mean values of motility parameters. © 2017 International Society for Advancement of Cytometry.

Seminal plasma proteins modify the distribution of sperm subpopulations in cryopreserved semen of rams with lesser fertility

Any physiological mechanism involved in sperm selection and semen improvement has effects on heterogeneous sperm populations. This is mainly due to the fact that sperm populations within a single ejaculate have considerable heterogeneity for many variables, such as motility which is meaningful in terms of understanding how some sperm cells possess fertility advantages as compared with other cells. In the present research, initially there was a multivariate and clustering analysis used to assess sperm motility data from cryopreserved ram semen to identify subpopulations and compare the distribution of these clusters between rams with lesser and greater fertility. There were four classifications made of sperm subpopulations (clusters): CL1 fast/linear/progressive sperm; CL2 fast/non-linear sperm; CL3 very fast/linear sperm with vigorous beating and CL4 slow/non-linear sperm. Rams with greater fertility had a lesser proportion of sperm considered as "hyperactivated" (CL2) and a greater proportion of slow and non-linear sperm (CL4) than sperm of rams with lesser fertility. In addition, the effects were assessed for the capacity of seminal plasma (SP) and interacting SP proteins (iSPP) that were present during different seasons of the year to improve the distribution of sperm within subpopulations of semen from rams with lesser fertility. The iSPP and SP were obtained by artificial vagina (AV) and electroejaculation (EE) during breeding and non-breeding seasons and added to thawed semen. All the aggregates had a significant effect on the distribution of sperm subpopulations and effects differed among seasons of the year and depending on collection method used. Even though, future studies are needed to assess the contribution of each subpopulation on ram sperm fertility, it is important that a multivariate analysis be used to evaluate the effect of a treatment on sperm quality variables.