Current perspectives of CASA applications in diverse mammalian spermatozoa

Exploring altered bovine sperm trajectories by sperm tracking in unconfined conditions

Mammalian sperm motility is getting more relevant due to rising infertility rates worldwide, generating the need to improve conventional analysis and diagnostic approaches. Nowadays, computer assisted sperm analysis (CASA) technologies represent a popular alternative to manual examination which is generally performed by observing sperm motility in very confined geometries. However, under physiological conditions, sperm describe three-dimensional motility patterns which are not well reconstructed by the limited depth of standard acquisition chambers. Therefore, affordable and more versatile alternatives are needed. Here, a motility analysis in unconfined conditions is proposed. In details, the analysis is characterized by a significant longer duration -with respect to conventional systems- with the aim to observe eventually altered motility patterns. Brightfield acquisition in rectangular glass capillaries captured frozen-thawed bovine spermatozoa which were analyzed by means of a self-written tracking routine and classified in sub-populations, based on their curvilinear velocity. To test the versatility of our approach, cypermethrin -a commonly used pesticides- known to be responsible for changes in sperm motility was employed, assessing its effect at three different time-steps. Experimental results showed that such drug induces an increase in sperm velocity and progressiveness as well as circular pattern formation, likely independent of wall interactions. Moreover, this resulted in a redistribution of sperm with the rapid class declining in number with time, but still showing an overall velocity increase. The flexibility of the approach permits parameter modifications with the experimental needs, allowing us to conduct a comprehensive examination of sperm motility. This adaptability facilitated data acquisition which can be computed at different frame rates, extended time periods, and within deeper observation chambers. The suggested approach for sperm analysis exhibits potential as a valuable augmentation to current diagnostic instruments.

Human Sperm as an In Vitro Model to Assess the Efficacy of Antioxidant Supplements during Sperm Handling: A Narrative Review

Spermatozoa are highly differentiated cells that produce reactive oxygen species (ROS) due to aerobic metabolism. Below a certain threshold, ROS are important in signal transduction pathways and cellular physiological processes, whereas ROS overproduction damages spermatozoa. Sperm manipulation and preparation protocols during assisted reproductive procedures-for example, cryopreservation-can result in excessive ROS production, exposing these cells to oxidative damage. Thus, antioxidants are a relevant topic in sperm quality. This narrative review focuses on human spermatozoa as an in vitro model to study which antioxidants can be used to supplement media. The review comprises a brief presentation of the human sperm structure, a general overview of the main items of reduction-oxidation homeostasis and the ambivalent relationship between spermatozoa and ROS. The main body of the paper deals with studies in which human sperm have been used as an in vitro model to test antioxidant compounds, including natural extracts. The presence and the synergic effects of different antioxidant molecules could potentially lead to more effective products in vitro and, in the future, in vivo.

Motility Assessment of Ram Spermatozoa

For successful fertilisation to occur, spermatozoa need to successfully migrate through the female reproductive tract and penetrate the oocyte. Predictably, poor sperm motility has been associated with low rates of fertilisation in many mammalian species, including the ram. As such, motility is one of the most important parameters used for in vitro evaluation of ram sperm quality and function. This review aims to outline the mechanical and energetic processes which underpin sperm motility, describe changes in motility which occur as a result of differences in sperm structure and the surrounding microenvironment, and assess the effectiveness of the various methods used to assess sperm motility in rams. Methods of subjective motility estimation are convenient, inexpensive methods widely used in the livestock industries, however, the subjective nature of these methods can make them unreliable. Computer-assisted sperm analysis (CASA) technology accurately and objectively measures sperm motility via two-dimensional tracing of sperm head motion, making it a popular method for sperm quality assurance in domesticated animal production laboratories. Newly developed methods of motility assessment including flagellar tracing, three-dimensional sperm tracing, in vivo motility assessment, and molecular assays which quantify motility-associated biomarkers, enable analysis of a new range of sperm motion parameters with the potential to reveal new mechanistic insights and improve ram semen assessment. Experimental application of these technologies is required to fully understand their potential to improve semen quality assessment and prediction of reproductive success in ovine artificial breeding programs.

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.

Sperm Transcriptome Analysis Accurately Reveals Male Fertility Potential in Livestock

Nowadays, selection of superior male candidates in livestock as a source of frozen semen based on sperm quality at the cellular level is not considered accurate enough for predicting the potential of male fertility. Sperm transcriptome analysis approaches, such as messenger RNA levels, have been shown to correlate with fertility rates. Using this technology in livestock growth has become the principal method, which can be widely applied to predict male fertility potential in the livestock industry through the analysis of the sperm transcriptome. It provides the gene expression to validate the function of sperm in spermatogenesis, fertilization, and embryo development, as the parameters of male fertility. This review proposes a transcriptomic analysis approach as a high-throughput method to predict the fertility potential of livestock more accurately in the future.

Addition of seminal plasma proteins effecting the in vitro kinetic properties of canine spermatozoa

The objective of this study is to evaluate the changes in the motility and kinetic patterns of canine spermatozoa, capacitated and decapacitated, after the addition of seminal plasma protein fractions with different molecular weight. It has been proposed that proteins in seminal plasma support the survival of the spermatozoa and exert a dual effect: capacitation and decapacitation. The seminal plasma from fresh ejaculates was subjected to chromatographic separation and four protein fractions were obtained. Computer-assisted sperm analysis was used to determine the sperm subpopulations with specific motion and kinetic characteristics after incubation with each of the four protein fractions. Two-dimensional electrophoresis of the fractions that exhibit a significant effect on the capacitation and decapacitation was performed. By sperm class analyser, capacitation changes were observed in the sperm subpopulation with a high curvilinear velocity and amplitude of lateral head displacement incubated with the seminal plasma protein fraction with a high molecular weight, which was also reflected in the decreased linearity, straightness, and progressive motility. The sperm subpopulation incubated with the seminal plasma protein fraction with a low molecular weight seemed to undergo a process of decapacitation (decreasing of the curvilinear velocity, increasing of the linearity, straightness and showing progressive motility). Despite their ample panorama of actions, the role of seminal plasma proteins regarding capacitation and decapacitation is still undetermined.

Assessment of Chilling Injury in Boar Spermatozoa by Kinematic Patterns and Competitive Sperm-Oviduct Binding In Vitro

Sensitive detection of chilling injury in boar spermatozoa is required to evaluate novel hypothermic preservation concepts. The study’s aim was to examine whether analyses of motility patterns and sperm binding in a competitive oviduct explant assay (cOEA) sensitively detect chilling-induced alterations in sperm function. Semen samples (n = seven boars) were split into four subsamples by dilution either in Beltsville Thawing Solution (BTS) or Androstar® Plus and stored at 5 °C or 17 °C. Storage temperature had a significant effect on the distribution of spermatozoa in seven major kinematic clusters. The effect size of chilling at 5 °C as estimated by Cramer’s V was higher (p < 0.05) in the BTS medium (0.21) compared to AndroStar® Plus (0.11). Spermatozoa extended in Androstar® Plus had higher relative binding capacity compared to sperm in BTS (p < 0.05). Binding indices correlated with the percentage of viable, acrosome-intact (r = 0.62) and motile spermatozoa (r = 0.72, both p < 0.001). The cluster size of sperm with slow, vigorous movement was negatively correlated with sperm-oviduct binding (r = −0.43, p < 0.05). In conclusion, the cluster analysis of sperm kinematics and competitive sperm oviduct binding in vitro present meaningful biological tests to assess novel concepts for hypothermic semen preservation.

Origin, Migration, and Reproduction of Indigenous Domestic Animals with Special Reference to Their Sperm Quality

Simple Summary

Indigenous domestic animals are derived from “wild” ancestors that have been domesticated as far back as 11,000 BP. In this investigation, we concentrate on indigenous domestic animals such as cattle, sheep, goats, pigs, and chickens and consider their fertility potential. In South Africa alone, more than 60 indigenous domestic breeds have been listed, and by and large, their sperm quality is similar to high fertility exotic breeds. Why are these indigenous breeds important? Particularly during the last 7000 years, different races migrated with their domestic animals, mainly from Northern to Southern Africa, and the animals were exposed to droughts, food scarcity, and many endo- and ecto-parasites. Accordingly, these animals are well-adapted to the harsh conditions of Southern Africa, and it is important to include them in breeding programs to exploit their favorable traits.

Abstract

Indigenous domestic animals such as cattle, sheep, goats, pigs, and chickens have a natural resistance to endo- and ecto-parasites and are tolerant in terms of harsh environmental conditions. These species orginated from the Fertile Cresent between 12,000 and 10,000 BP before migrating into surrounding continents. In view of limited information on the reproductive status of indigenous breeds, it is important to examine their semen characteristics in order to select males to improve livestock production. We have largely relied on existing literature but also our published and ongoing research on sperm quality assessment of several indigenous breeds. The sperm quality of these breeds is similar to current commercial breeds and has been quantified using cutting-edge methods. In this context, we have presented sperm functional tests which provide a better estimate of semen quality than just a standard semen analysis. Initial results suggest that the indigenous breeds have a high sperm quality and sperm functionality similar to currently farmed exotic or crossbreeds. In the long-term, the importance of preserving the favorable traits of these breeds is a priority in view of crossbreeding with existing good meat and milk producers.

Comparison of two staining techniques on the manual and automated canine sperm morphology analysis

Detailed and direct analysis of semen, including sperm morphology, enables a diagnosis of male fertility. This study aimed to describe an economical and verified protocol for canine spermiograms and compare the effectiveness of Sperm Stain^® and Sperm Blue^® (Microptic, Spain) in veterinary practice. Sperm assessment was conducted manually, using a standard optical microscope, and via computerized semen analysis using the SCA^® CASA (Sperm Class Analyzer^® CASA System‐MICROPTIC, Spain). This study showed that Sperm Blue^® is a better solution for computerized sperm quality analysis of healthy dogs. At the same time, Sperm Stain^® turned out to be more helpful in identifying specific morphological defects of sperm. Automated canine sperm morphology analysis worked better with Sperm Blue stain, but Sperm Stain simplified manual evaluation of various organelles’ defects. Standard, manual examination is more error‐prone for an inexperienced andrology technician, but it seems to be still a gold standard technique for canine sperm assessment.

Effect of Copper Sulphate and Cadmium Chloride on Non-Human Primate Sperm Function In Vitro

In order to address the large percentage of unexplained male infertility in humans, more detailed investigations using sperm functional tests are needed to identify possible causes for compromised fertility. Since many environmental and lifestyle factors might be contributing to infertility, future studies aiming to elucidate the effect of such factors on male fertility will need the use of appropriate research models. The current study aimed to assess the effects of two heavy metals, namely copper sulphate, and cadmium chloride, on non-human primate (NHP) sperm function in order to establish the possibility of using these primate species as models for reproductive studies. Our combined results indicated that the functionality of NHP spermatozoa is inhibited by the two heavy metals investigated. After in vitro exposure, detrimental effects, and significant lowered values (p < 0.05) were obtained for sperm motility, viability and vitality, acrosome intactness, and hyperactivation. These metals, at the tested higher concentrations, therefore, have the ability to impair sperm quality thereby affecting sperm fertilizing capability in both humans and NHPs.

Semen evaluation: methodological advancements in sperm quality-specific fertility assessment - A review

Assessment of male fertility is based on the evaluation of sperm. Semen evaluation measures various sperm quality parameters as fertility indicators. However, semen evaluation has limitations, and it requires the advancement and application of strict quality control methods to interpret the results. This article reviews the recent advances in evaluating various sperm-specific quality characteristics and methodologies, with the help of different assays to assess sperm-fertility status. Sperm evaluation methods that include conventional microscopic methods, computer-assisted sperm analyzers (CASA), and flow cytometric analysis, provide precise information related to sperm morphology and function. Moreover, profiling fertility-related biomarkers in sperm or seminal plasma can be helpful in predicting fertility. Identification of different sperm proteins and diagnosis of DNA damage has positively contributed to the existing pool of knowledge about sperm physiology and molecular anomalies associated with different infertility issues in males. Advances in methods and sperm-specific evaluation has subsequently resulted in a better understanding of sperm biology that has improved the diagnosis and clinical management of male factor infertility. Accurate sperm evaluation is of paramount importance in the application of artificial insemination and assisted reproductive technology. However, no single test can precisely determine fertility; the selection of an appropriate test or a set of tests and parameters is required to accurately determine the fertility of specific animal species. Therefore, a need to further calibrate the CASA and advance the gene expression tests is recommended for faster and field-level applications.

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.

Evaluation of the Morphometry of Sperm from the Epididymides of Dogs Using Different Staining Methods

Evaluation of sperm morphometry is an important criterion in the diagnosis of a male animal's suitability for breeding. The aim of the study was to evaluate the morphometry of sperm from the epididymides of dogs subjected to routine castration using various staining methods. The study was carried out on semen collected from ten healthy dogs. Gonads were obtained from each dog during routine castration at a veterinary surgery. Then, the epididymides (caput, corpus, cauda) were isolated from the gonads, semen was collected from them and microscope slides were prepared. The slides for evaluation of sperm morphometry were prepared by four methods: DiffQuik, SpermBlue, eosin-nigrosin and eosin-gentian. A total of 2400 sperm were analyzed (240 sperm from the dog). The sperm collected from the caput and corpus of the epididymis were found to have larger heads and tails than those collected from the cauda of the epididymis. The staining method was shown to affect the morphometry of sperm taken from the epididymides of dogs. The staining methods differentiate the dimensions of the head of sperm in different parts of the epididymis but do not affect the length of the sperm tail. The occurrence of differences in the head dimensions of sperm may be linked to the use of different fixatives and chemical reagents in the staining procedure. Sperm stained by the EN method had the smallest head and tail dimensions. The greatest head area was noted in the sperm stained by the EG method. In the slides stained by the SB method, the sperm heads were relatively long but narrow. The methods used are suitable for the evaluation of sperm structure, and the possibility of using all four methods enables a full characterization of sperm collected from the caput, corpus and cauda of the epididymides of dogs.

Sperm motility, kinematics, morphometry and morphology over two seasons in free-ranging African elephants (Loxodonta africana)

This study aimed to address the lack of information on quantitative semen and sperm characteristics of free-ranging African elephants. Nineteen ejaculates were collected from 12 elephant bulls by means of electroejaculation in spring (Season 1, end of dry season, n=7) and in autumn (Season 2, end of rainy season, n=12). While most elephant cows are in oestrus in the rainy season, it is not evident whether sperm quality also improves during this period. Semen samples were assessed using computer-aided sperm analysis (CASA), brightfield microscopy and transmission electron microscopy. Seasonal differences and individual variation in sperm quality of bulls were apparent, with ejaculates collected during Season 2 revealing higher percentages for total motility, progressive motility, rapid-swimming spermatozoa and kinematic parameters compared with Season 1 (P<0.05). Although normal sperm morphology percentage was similar over the two seasons, more sperm tail defects were found in Season 2 (P<0.05). The baseline reference data and multivariate sperm parameter associations reported in this study can be used to predict elephant bull sperm quality and potential to fertilise. It is clear that CASA can detect subtle differences in sperm quality of African elephant ejaculates and should be the approach for future investigations.

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.

Tetrazolium Salt WST-8 as a Novel and Reliable Chromogenic Indicator for the Assessment of Boar Semen Quality

Simple Summary

Good semen quality is an essential factor for breeding success when artificial insemination is performed. However, semen quality can not fully be evaluated by merely sperm viability or motility. Standard semen quality evaluation requires costly automated computer-assisted sperm analysis or specific and laborious labeling procedures before particular parameters can be assessed by flow cytometry. In the current study, we examined whether the 2-[2-methoxy-4-nitrophenyl]-3-[4-nitrophenyl]-5-[2,4-disulfophenyl]-2H-tetrazolium (WST-8) assay, which is widely used in the cell biology field, can be applied to evaluate sperm viability, and moreover, whether the WST-8 reduction rate can correlate with multiple sperm parameters that are related to sperm quality. We demonstrated in this study that the WST-8 assay can be used as a rapid, affordable, and reliable method for the prediction of semen quality in boar.

Abstract

A tetrazolium salt, 2-[2-methoxy-4-nitrophenyl]-3-[4-nitrophenyl]-5-[2,4-disulfophenyl]-2H-tetrazolium (WST-8), has been used widely to determine cell viability; however, its application in the field of reproduction is still limited due to this assay merely providing information regarding cell viability. The aim of this study was to correlate the WST-8 reduction rate with various sperm quality-related parameters (i.e., sperm viability, motility, progressive motility, acrosome integrity and mitochondria integrity) in order to provide a rapid, reliable and affordable assessment for boar semen quality evaluation. Using different ratios of active/damaged sperm cells, we first validated our sample preparations by standard flow cytometry and computer-assisted sperm analysis. Further analyses demonstrated that the most efficient experimental condition for obtaining a reliable prediction model was when sperm concentration reached 300 × 10⁶ cells/mL with the semen/cell-counting kit-8 (CCK-8^®) ratio of 200/10 and incubated time of 20 min. Under this set up, the WST-8 reduction rate (differences on optic density reading value, ΔOD at 450 nm) and sperm parameters were highly correlated (p < 0.01) for all sperm parameters evaluated. In the case of limited semen samples, a minimal semen concentration at 150 × 10⁶ cells/mL with the semen/CCK-8^® ratio of 200/20 and incubation time for 30 min could still provide reliable prediction of sperm parameters using the WST-8 assay. Our data provide strong evidence for the first time that the WST-8 assay could be used to evaluate boar semen quality with great potential to be applied to different mammalian species.

Optimal frame rate when there were stallion sperm motility evaluations and determinations for kinematic variables using CASA-Mot analysis in different counting chambers

This study was conducted to determine optimum image capture frame rates (FRO) when there was evaluation of different types of counting chambers used for CASA-Mot determinations of stallion sperm motility. Sperm VCL was determined at frame rates of 25-250 f/s in: 1) Spermtrack® (Spk) 10 and 20 chambers (drop displacement-type chambers 10 and 20 μm-deep respectively; and 2) ISAS®D4C10, ISAS®D4C20 (10 and 20 μm-deep respectively) and ISAS®D4C20 L (20 μm-deep) capillary loaded chambers. Values for different sperm kinematic variables were determined using each chamber at 250 f/s, which is the maximum frame rate that the software can be used for analyses. With evaluation of Spk chambers, there was a greater curvilinear velocity (VCL), average path velocity (VAP), straight line velocity (STR), amplitude of lateral head displacement (ALH) and beat cross frequency (BCF) values (P < 0.05) than with capillary loaded chambers, with there being greatest values with 20 μm-deep chambers. With the Spk10 chamber, VCL and ALH were greater at the chamber centre than periphery. There were no such differences for the Spk20 chamber. With evaluation of the D4C10 chamber, VSL and STR were less when there was a sperm deposition point towards the chamber end, while there were the opposite for the D4C20 chamber. When there was evaluation of the D4C20 chamber, there were also greater VCL, WOB and BCF values in distal areas. With use of most of these chambers, data should be collected from different fields and means determined, however, this is not necessary with Spk20 chambers.

Morphometric Characteristics of the Spermatozoa of Blue Fox (Alopex lagopus) and Silver Fox (Vulpes vulpes)

Simple Summary

The present study describes a detailed morphometric analysis of the sperm of the blue fox (Alopex lagopus) and silver fox (Vulpes vulpes), together with determination of the shape indices of the sperm head. Staining with silver nitrate enables precise identification of the acrosome and reveals structural details of the sperm tail, so that they can be accurately measured. Statistically significant differences were found for most of the morphometric parameters of the two fox species. The blue fox sperm were generally larger, but the acrosome area and coverage were greater in the silver fox. There are no clear recommendations regarding sperm staining techniques for foxes, and no reference values for morphometric parameters of the sperm of foxes or for canines in general. Staining with silver nitrate for evaluation of the morphometry of fox sperm can be used as an independent technique or an auxiliary technique in routine analysis of canine semen.

Abstract

The results presented in this study are the first such extensive characterization of the sperm morphometry of the blue fox (Alopex lagopus) and silver fox (Vulpes vulpes), as representatives of the family Canidae. Canine spermatozoa, especially the sperm of farmed foxes, are not often described in studies on reproduction. The aim of the study was a detailed comparison of the morphometric dimensions and shape of the sperm of two fox species: silver fox and blue fox. Semen collected from 10 silver foxes and 10 blue foxes was used for the study. The specimens were stained with silver nitrate. Measurements were performed of the length, width, perimeter, and area of the head; the area of the acrosome and its coverage; the length of the midpiece and its coverage; the length of the tail; and the length of the end piece of the tail. In addition, four head shape indices were calculated: ellipticity, elongation, roughness and regularity. The following values for the morphometric parameters and shape indices were obtained for blue fox and silver fox, respectively: head length—6.72 µm and 6.33 µm; head width—4.54.µm and 4.21 µm; head perimeter—18.11 µm and 17.37 µm; head area—21.94 µm² and 21.11 µm²; acrosome area—11.50 µm² and 10.92 µm²; midpiece length—12.85 µm and 12.79 µm; tail end piece length—3.44 µm and 3.28 µm; tail length—65.23 µm and 65.09 µm; acrosome coverage—52.43% and 52.83%; midpiece coverage—19.71% and 19.65%; sperm length—71.95 µm and 71.42 µm; ellipticity—1.49 and 1.52; elongation—0.19 and 0.20; roughness—0.84 and 1.88; regularity—1.09 and 0.99. The significance of differences between species was verified by Tukey’s test at p ≤ 0.05. Statistically significant differences between species were found for the following parameters: head length, width, perimeter and area; acrosome area; tail, end piece, and total sperm length; roughness and regularity. The differences in the size and shape of sperm can be used to establish reference patterns for fox sperm enabling more accurate species identification.

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.

Methodological considerations for examining the relationship between sperm morphology and motility

Sperm cells of all taxa share a common goal to reach and fertilize an ovum, yet sperm are one of the most diverse cell types in nature. While the structural diversity of these cells is well recognized, the functional significance of variation in sperm design remains elusive. An important function of spermatozoa is a need to migrate toward the ova, often over long distances in a foreign environment, which may include a complex and hostile female reproductive tract. Several comparative and experimental studies have attempted to address the link between sperm morphology and motility, yet the conclusions drawn from these studies are often inconsistent, even within the same taxa. Much of what we know about the functional significance of sperm design in internally fertilizing species has been gleaned from in vitro studies, for which experimental parameters often vary among studies. We propose that discordant results from these studies are in part due to a lack of consistency of methods, conditions that do not replicate those of the female reproductive tract, and the overuse of simple linear measures of sperm shape. Within this review, we provide a toolkit for imaging, quantifying, and analyzing sperm morphology and movement patterns for in vitro studies and discuss emerging approaches. Results from studies linking morphology to motility enhance our understanding of the evolution of adaptive sperm traits and the mechanisms that regulate fertility, thus offering new insights into methods used in assisted reproductive technologies in animal science, conservation and public health.

Computer Aided Sperm Analysis (CASA) in domestic animals: Current status, three D tracking and flagellar analysis

Computer Aided Sperm Analysis is currently well established in domestic animals. Apart from sperm concentration and sperm motility assessment (percentage groupings, kinematics groupings) sperm morphology, sperm viability, sperm fragmentation and the acrosome reaction are automated as part of modern CASA systems. This review cum new original research paper focuses on providing baseline data on sperm concentration and motility in common domestic species of animals of proven fertility including bull, boar, horse, ram, goat, dog, donkey, chicken. There is a great need to establish quantitative baseline values for sperm quality, breed differences and to develop and apply relevant sperm functional tests that relates to fertilization outcome. These approaches need to be standardized. Two new approaches are presented in this work that are complimentary to CASA and provide a whole range of new visualizations and parameters that may assist to define sperm function and quality better. The first new approach shows how Two-D analysis using X and Y coordinates of CASA can be converted to Three-dimensional (3^D) tracks. This method shows how sperm movement can be visualized in 3^D despite several shortcomings. The second approach of flagellar analysis through the use of the FAST programme (Flagellar and Sperm Tracking) of the University of Birmingham group represents a new development and provides several new quantitative measures such as flagellar speed and energy output (in Watts) expended by each sperm. Together with CASA and other sperm functional parameters, FAST may provide new and novel insights in sperm biology and assist in fertility assessment.

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.

Combined effects of type and depth of counting chamber, and rate of image frame capture, on bull sperm motility and kinematics

Semen quality assessment requires accurate, reliable and objective methods for examination of sperm variables including sperm motility. For preparation of semen samples for artificial insemination, as a genetic resource, samples that are used for insemination need to have the capacity to result in a highly acceptable fertility rate. Several methods have been developed for evaluation of bull sperm in laboratory conditions and for preparation of doses for artificial insemination. Computer-assisted semen analyses can provide objective information on various sperm variables. Nevertheless, this equipment requires fine-calibrations considering differences among species, breeds and conditions for sample evaluation and data analyses. In the present study, there was examination of the interaction between factors such as image frame rate and type and depth of counting chamber in which sperm were evaluated, together with differences between bulls of four breeds. The use of the Spermtrack® reusable 10 μm-depth chamber provided more reliable results than results obtained using disposable chambers (10 and 20 μm depth). A capture rate of at least 90 fps is required for assessment of sperm motility percentage, whereas a rate of 250 fps is needed for obtaining consistent kinematic data. Differences among breeds in the present study indicate conditions for sperm analyses should include specific equipment calibrations for each breed. These results contribute to development of more precise conditions for assessments of bull sperm quality taking into account breed differences and the requirement each breed has for the adequate evaluation and preparation of samples for artificial insemination.

Kinematic and head morphometric characterisation of spermatozoa from the Brown Caiman (Caiman crocodilus fuscus)

The development of analytical methods for the evaluation of crocodilian semen is an important component for the assessment of male breeding soundness and the development of assisted breeding technology in this taxon. Computer-Assisted Semen Analysis (CASA) technology is becoming an increasingly common technique in seminal evaluations for animals but there has been no application of this technique for reptilian spermatozoa. The aim of this study was to analyse sperm kinematic and morphometric variables in Caiman crocodilus fuscus semen samples and to determine whether there were sperm subpopulations. Four ejaculates from four sexually mature captive caimans were used for this study. A CASA-Mot and CASA-Morph system was used with an image acquisition rate of 50 Hz for 2 s of capture. The ISAS^®D4C20 counting chambers were used and spermatozoa incubated at 25 °C. Total and progressive motilities did not differ among animals (P > 0.05). There was a significant animal effect in the model with respect to sperm morphometry, and kinematic indices including linearity (LIN) and straightness (STR) (P < 0.05). Results for principal component (PC) analysis indicated variables were grouped into four components: PC₁ related to velocity, PC₂ to progressivity, PC₃ to oscillation and PC₄ to sperm path cross-linking. Subpopulation (SP) structure analysis indicated there were four groups, namely, rapid non-progressive (SP₁), slow non-progressive (SP₂), rapid progressive (SP₃) and medium progressive (SP₄), representing 14.5%, 45.4%, 18.7%, and 21.4% respectively. Findings in the present study indicate the importance of continuing development of reliable protocols regarding the standardisation of computer-based semen analyses in reptilian species.

Quantitative assessment of heavy metal effects on sperm function using computer-aided sperm analysis and cytotoxicity assays

One known environmental risk factor impacting on human reproduction is heavy metal pollution. Although some metals (e.g., Cu, Se and Zn) have protective effects on the male reproductive system in low doses, heavy metals can accumulate to toxic levels and result in poor semen quality and decreased sperm function. We investigated the effect of CuSO₄ and CdCl₂ (10, 50, 100 and 250 µg/ml or 500 µg/ml) on human sperm motility and vitality by using computer-aided sperm analysis (CASA) and two cytotoxicity assays (WST-1 and XTT). Several sperm motility parameters were significantly reduced after 5 hr of exposure to the highest concentrations of CuSO₄ (250 µg/ml) and CdCl₂ (500 µg/ml). The WST-1 assay also revealed significantly lower absorbance values for 50, 100 and 250 µg/ml CuSO₄ and for 500 µg/ml CdCl₂ ; however, no significant effect was seen with XTT. The calculated average IC₅₀ value was 50.31±  4.34 µg/ml for CuSO₄ and 392.32  ±76.79 µg/ml for CdCl₂ . The effects of these metals were confirmed with MgCl₂ , a positive control. This study provides threshold concentrations for the harmful effect of CuSO₄ and CdCl₂ on human spermatozoa and recommends the use of WST-1 as vitality assay in future in vitro studies.

Sperm kinematic characterization of alpaca (Vicugna pacos L.) during the reproductive season

Semen analysis is a key factor when determining the fertility ability in males. South American camelids, and in particular the alpaca, have been studied very little when compared with other farm animals. The aim of this work was to perform the kinematic characterization of alpaca spermatozoa collected directly from the deferent duct by using CASA-Mot (Computer Assisted Semen Analysis for Motility) technology. Samples were obtained every three days throughout the reproductive season during two periods and with a break of seven days in the middle. During both periods, the quality of the sample's motility and kinematics increased over the first two days and then subsequently decreased. This pattern was similar in all animals. It was concluded that the introduction of resting times can be useful to improve sperm quality for artificial insemination purposes in natural conditions.