Effect of Season on the Characteristics of Warmblood Stallion Spermatozoa Stored in a Liquid State at 5 °C

The aim of this study was to investigate the effect of season (breeding vs. non-breeding) on the characteristics of warmblood stallion spermatozoa during liquid storage. Ejaculates were collected from eight stallions during the breeding and non-breeding seasons (March-July and September-December, respectively) and were diluted in an EquiPro extender. Semen was stored for up to 96 h at 5 °C. Analysis of stored sperm included the assessment of motility (CASA system), acrosomes with normal apical ridges (NAR), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), and adenosine triphosphate (ATP) content. In sperm stored for up to 24 h, the values of the following parameters were higher (p ≤ 0.05) in March-July than in September-December: progressive motility (PMOT), PMI, MMP, beat cross frequency (BCF), and linearity (LIN). The values of the studied parameters decreased during storage, and the observed changes were affected by season. The values of NAR, PMI and MMP, average path velocity (VAP), straight line velocity (VSL), and curvilinear velocity (VCL) decreased (p ≤ 0.05) after 24 h of storage during the breeding season, whereas a significant decrease in these parameters was observed after prolonged storage (48 h or longer) during the non-breeding seasons. Cooled sperm of warmblood stallions collected during the breeding season was characterized by higher initial quality than the sperm collected during the non-breeding season. However, sperm sampled during the non-breeding season appeared to be more resistant to cold shock, which increases their suitability for cold storage at 5 °C. Stallion sperm sampled in both seasons were characterized by similar suitability for liquid storage. Further research is needed to assess the fertilizing capacity of stored sperm.

Effect of bicarbonate and polyvinyl alcohol on in vitro capacitation and fertilization ability of cryopreserved equine spermatozoa

BACKGROUND

Factors contributing to the limited success of in vitro fertilization in horses remain to be studied. In this work, we elucidated the effect of different essential capacitation media components, bicarbonate, and bovine serum albumin or polyvinyl-alcohol, and the incubation microenvironment on sperm parameters associated with capacitation, acrosome reaction, and their ability to activate oocytes via heterologous intracytoplasmic spermatozoa injection in equine cryopreserved spermatozoa.

METHODS

Frozen-thawed spermatozoa underwent incubation at different time intervals in either Tyrode's albumin lactate pyruvate medium (non-capacitating; NC) or Tyrode's albumin lactate pyruvate supplemented with bicarbonate, bicarbonate and polyvinyl-alcohol, bicarbonate and bovine serum albumin, polyvinyl-alcohol and bovine serum albumin alone. Protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels, sperm motility, and acrosome reaction percentages were evaluated. After determining the best condition media (capacitating; CAP), heterologous intracytoplasmic spermatozoa injection on pig oocytes was performed and the phospholipase C zeta sperm localization pattern was evaluated.

RESULTS

Incubation of frozen-thawed equine spermatozoa with bicarbonate and polyvinyl-alcohol in atmospheric air for 45 min induced an increase in protein kinase A-phosphorylated substrates and tyrosine phosphorylation levels compared to NC condition. Sperm incubation in bicarbonate and polyvinyl-alcohol medium showed an increase in total motility and progressive motility with respect to NC (p ≤ 0.05). Interestingly, three parameters associated with sperm hyperactivation were modulated under bicarbonate and polyvinyl-alcohol conditions. The kinematic parameters curvilinear velocity and amplitude of lateral head displacement significantly increased, while straightness significantly diminished (curvilinear velocity: bicarbonate and polyvinyl-alcohol = 120.9 ± 2.9 vs. NC = 76.91 ± 6.9 µm/s) (amplitude of lateral head displacement: bicarbonate and polyvinyl-alcohol = 1.15 ± 0.02 vs. NC = 0.77 ± 0.03 µm) (straightness: bicarbonate and polyvinyl-alcohol = 0.76 ± 0.01 vs. NC = 0.87 ± 0.02) (p ≤ 0.05). Moreover, the spontaneous acrosome reaction significantly increased in spermatozoa incubated in this condition. Finally, bicarbonate and polyvinyl-alcohol medium was established as CAP medium. Although no differences were found in phospholipase C zeta localization pattern in spermatozoa incubated under CAP, equine spermatozoa pre-incubated in CAP condition for 45 min showed higher fertilization rates when injected into matured pig oocytes (NC: 47.6% vs. CAP 76.5%; p ≤ 0.05).

CONCLUSION

These findings underscore the importance of bicarbonate and polyvinyl-alcohol in supporting critical events associated with in vitro sperm capacitation in the horse, resulting in higher oocyte activation percentages following heterologous intracytoplasmic spermatozoa injection. This protocol could have an impact on reproductive efficiency in the equine breeding industry.

Assessment of Sperm Motility with the Use of Computer-Aided Sperm Analysis (CASA)

Sperm motility assessment by computer-aided sperm analysis (CASA) is an objective and quantitative method evaluating many sperm motility parameters such as percentage groupings and sperm kinematics rapidly. It is superior to manual assessment of sperm motility, which has been shown to be inconsistent and not repeatable. Modern CASA systems have been expanded to also incorporate automated modules dealing with, among others, sperm morphology, sperm vitality, DNA fragmentation, and the acrosome reaction. This chapter provides the background for the necessity and usefulness of CASA. The focus is mainly on human spermatozoa but information on animal spermatozoa is also provided.

Effect of protein acetylation on capacitation of stallion sperm

Sperm capacitation is considered the main factor limiting conventional in vitro fertilization (IVF) in horses. A recent scientific breakthrough in sperm processing for IVF in horses has resulted in embryos and foals being produced; however, various aspects of the IVF process remain to be fully elucidated. Lysine acetylation has been shown to play a role in sperm capacitation in several species and the objective of this study was to detect and evaluate this process in the horse. Ejaculates of two stallions were collected and incubated in different conditions with deacetylase inhibitors to induce a hyperacetylation state. Although lysine acetylation was successfully detected in all experimental groups, sperm hyperacetylation could not be induced following incubation with deacetylase inhibitors. In addition, no hyperactivation was detected by kinematic sperm evaluation and tyrosine phosphorylation increased only in the positive control group. Treatments with high doses of deacetylase inhibitors increased acrosome reaction indicating a possible connection between induction of acrosome reaction and protein acetylation. Future studies investigating the effect of longer incubation periods with different doses of deacetylase inhibitors are warranted to elucidate the ability of protein acetylation to induce capacitation of stallion sperm.

Effect of exogenous sperm capacitation inducers on stallion sperm

Although under appropriate laboratory conditions, sperm from different mammalian species can be capacitated in vitro, the optimal conditions for sperm capacitation in the stallion have been elusive. This study evaluated the effect of different capacitating inducers in Whitten and Tyrode media and assessed their impact on capacitation-related factors. Stallion sperm were incubated with different combinations of capacitating inducers at 38.5 °C in an air atmosphere. Sperm quality variables such as motility, mitochondrial membrane potential, and lipid peroxidation were assessed. Membrane fluidity and intracellular calcium levels were evaluated as early markers of capacitation, while tyrosine phosphorylation events and the sperm's ability to perform acrosomal exocytosis were used as late capacitation markers. Finally, these sperm were evaluated using a heterologous zona pellucida binding assay. The findings confirm that capacitating conditions evaluated increase intracellular calcium levels and membrane fluidity in both media. Similarly, including 2 or 3 inducers in both media increased tyrosine phosphorylation levels and acrosomal exocytosis after exposure to progesterone, confirming that stallion sperm incubated in these conditions shows cellular and molecular changes consistent with sperm capacitation. Furthermore, the zona pellucida binding assay confirmed the binding capacity of sperm incubated in capacitation conditions, a key step for stallion in vitro fertilization success. Further studies are needed to evaluate the effect of these conditions on in vitro fertilization in the horse.

Effect of sperm treatment with lysolecithin on in vitro outcomes of equine intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) in horses is currently employed for clinical and commercial uses, but the protocol could be optimized to improve its efficiency. We have hypothesized that destabilization of plasma and acrosomal membranes prior to injection would positively impact the developmental potential of equine zygotes generated by ICSI. This study evaluated effects of the sperm treatment with lysolecithin on plasma and acrosomal membranes and on oocyte activation ability, initially following heterologous ICSI on bovine oocytes and subsequently employing equine oocytes. The effects of the lysolecithin -treatment on the efficiency of conventional and piezo-assisted equine ICSI were evaluated. To do this, the equine sperm were treated with different concentrations of lysolecithin and the sperm plasma membrane, acrosome and DNA integrity were evaluated by flow cytometry. The results showed that a lysolecithin concentration of 0.08 % destabilized the membranes of all sperm and affected DNA integrity within the range described for the species (8-30 %). In addition, the heterologous ICSI assay showed that lysolecithin treatment was detrimental to the sperm's ability to activate the oocyte, therefore, chemical oocyte activation was used after equine ICSI after injection with lysolecithin -treated sperm. This group showed similar developmental rate to the control group with and without exogenous activation. In conclusion, lysolecithin pre-treatment is not necessary when using ICSI to produce equine embryos in vitro. The results from the current study provide additional insight regarding the factors impacting ICSI in horses.

Progesterone and estradiol regulate sperm hyperactivation and in vitro fertilization success in mice

Progesterone (P) and 17β-estradiol (Eβ) form the well-known hormone pair that regulates sperm capacitation. Here, we examined the regulatory effects of P and Eβ on sperm hyperactivation in mice and evaluated the in vitro fertilization (IVF) success. Although P enhanced hyperactivation, Eβ dose-dependently suppressed the P-enhanced hyperactivation. Moreover, P increased IVF success, whereas Eβ suppressed the P-induced increase in IVF success in a dose-dependent manner. Thus, P and Eβ competitively regulate hyperactivation and IVF success in mice. Since P and Eβ concentrations generally change during the estrous cycle, sperm are speculated to capacitate in response to the oviductal environment and fertilize the oocyte.

Predicting the Outcome of Equine Artificial Inseminations Using Chilled Semen

This study aimed to determine whether an analysis of stallion ejaculate could accurately predict the likelihood of pregnancy resulting from artificial insemination in mares. This study involved 46 inseminations of 41 mares, using 7 standardbred stallions over a 5-week period at an Australian pacing stud. Semen quality was assessed immediately after collection and again after chilling at ~5 °C for 24 h. The assessment involved evaluating ejaculate volume, sperm concentration, and motility parameters using an iSperm^® Equine portable device. After the initial evaluation, a subpopulation of cells was subjected to a migration assay through a 5 µm polycarbonate filter within a Samson™ isolation chamber over a 15 min period. The cells were assessed for their concentration, motility parameters, and ability to reduce the membrane impermeant tetrazolium salt WST-1. The data, combined with the stallion and mare's ages, were used to predict the likelihood of pregnancy, as confirmed by rectal ultrasound sonography performed 14 days post ovulation. The criteria used to predict pregnancy were optimized for each individual stallion, resulting in an overall accuracy of 87.9% if analyzed pre-chilling and 95% if analyzed post-chilling. This study suggests that an analysis of stallion ejaculate can be used to predict the likelihood of pregnancy resulting from artificial insemination in mares with a high level of accuracy.

Modulatory effect of MG-132 proteasomal inhibition on boar sperm motility during in vitro capacitation

A series of biochemical and biophysical changes during sperm capacitation initiates various signaling pathways related to protein phosphorylation leading to sperm hyperactivation, simultaneously with the regulation of proteasomal activity responsible for protein degradation and turnover. Our study aimed to unveil the role of the proteasome in the regulation of boar sperm motility, hyperactivated status, tyrosine phosphorylation, and total protein ubiquitination. The proteolytic activity of the 20S proteasomal core was inhibited by MG-132 in concentrations of 10, 25, 50, and 100 μM; and monitored parameters were analyzed every hour during 3 h of in vitro capacitation (IVC). Sperm motility and kinematic parameters were analyzed by Computer Assisted Sperm Analysis (CASA) during IVC, showing a significant, negative, dose-dependent effect of MG-132 on total and progressive sperm motility (TMOT, PMOT, respectively). Furthermore, proteasomal inhibition by 50 and 100 μM MG-132 had a negative impact on velocity-based kinematic sperm parameters (VSL, VAP, and VCL). Parameters related to the progressivity of sperm movement (LIN, STR) and ALH were the most affected by the highest inhibitor concentration (100 μM). Cluster analysis revealed that the strongest proteasome-inhibiting treatment had a significant effect (p ≤ 0.05) on the hyperactivated sperm subpopulation. The flow cytometric viability results proved that reduced TMOT and PMOT were not caused by disruption of the integrity of the plasma membrane. Neither the protein tyrosine phosphorylation profile changes nor the accumulation of protein ubiquitination was observed during the course of capacitation under proteasome inhibition. In conclusion, inhibition of the proteasome reduced the ability of spermatozoa to undergo hyperactivation; however, there was no significant effect on the level of protein tyrosine phosphorylation and accumulation of ubiquitinated proteins. These effects might be due to the presence of compensatory mechanisms or the alteration of various ubiquitin-proteasome system-regulated pathways.

Effects of Extenders Supplementation with Gum Arabic and Antioxidants on Ram Spermatozoa Quality after Cryopreservation

Semen cryopreservation is very important in animal agriculture to maximize the number of daughters of genetically superior males and to distribute the cryopreserved semen of good males all over the world. However, the freezing process generates some damage to sperm that reduce their fertilizing ability after thawing. Moreover, egg yolk, which is the most common animal-origin cryoprotectant used in semen dilution, is considered a source of biosecurity risk. In the current study, we aimed to compare the replacement of egg yolk in the extender by gum arabic (5%) along with supplementation with antioxidant cysteine or ascorbic acid on semen quality and freezability in Noemi rams in vitro. Semen from six rams were collected with an artificial vagina two times per week. Semen evaluation parameters such as color, volume, pH, general motility, percentage motility, concentration and cell viability ratio were assessed. Spermatozoa motility and concentration were estimated with the computer-assisted semen analysis system. The semen samples were frozen using a Tris extender containing either 15% egg yolk or 5% gum arabic. For antioxidant-supplemented extenders, cysteine or ascorbic acid was dissolved at concentrations of 0.10, 0.50 or 1.0 mM in egg yolk or gum arabic extender. The semen from each ejaculate of each ram were resuspended with a specific extender with glycerol (5%); the final volume after dilution was 1 mL semen to 4 mL extender. The samples were then cooled to 4 °C for 120 min, loaded into 0.5 mL straws and frozen in liquid nitrogen for 7 days. Supplementation of gum arabic or egg yolk extenders for ram semen with antioxidants such as cysteine or ascorbic acid has beneficial effects on semen quality after cold storage or cryopreservation. However, supplementation of a 5% gum arabic extender with cysteine at 0.5 or 1 mM concentration or ascorbic acid at 0.5 mM concentration improved the quality of spermatozoa postcryopreservation. It could be concluded that gum arabic is a good alternative for egg yolk in Noemi ram semen extenders. Antioxidants are necessary to support the addition of gum arabic to the extender to help the ram spermatozoa to survive freezing-thawing and oxidative stresses.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

Relationships between Biomarkers of Oxidative Stress in Seminal Plasma and Sperm Motility in Bulls before and after Cryopreservation

This study aimed at evaluating the relationship between biomarkers of oxidative stress (OS) in seminal plasma and sperm motility in bulls before and after cryopreservation. Three ejaculates per bull were collected from 20 young bulls. Each ejaculate was analyzed for motility before and after cryopreservation (by CASA), and the SP concentration of Advanced Oxidation Protein Products (AOPP), thiols, and carbonyl groups (CT) were examined. Then, based on their motility, the ejaculates were grouped into: high motility fresh (HMF), low motility fresh (LMF), high motility thawed (HMT), and low motility thawed (LMT) groups. Higher AOPP and thiol concentrations on SP were related (p < 0.05) to the higher LIN and BCF and lower ALH of fresh semen. In addition, AOPP and thiols were significantly higher in HMF than LMF. As a confirmation of this, the Receiver Operating Characteristic (ROC) curve analysis showed that AOPP and thiol concentrations in SP were able to discriminate between HMF and LMF ejaculates (Area Under the Curve of 71.67% and 72.04%, respectively). These observations give an alternative perspective on the relationship between sperm motility and the OS parameters of SP, which need further investigations.

Effect of cholestanol and cholesterol-loaded cyclodextrin on stallion sperm function and capacitation post-cryopreservation

Cryopreservation of stallion semen is less efficient than other species such as bovine. This is mainly because of the greater susceptibility of stallion sperm to the freezing damage that generates oxidative stress and plasma membrane injury, resulting in DNA fragmentation and cell death. These data suggest the need to develop new strategies of sperm cryopreservation that can improve the efficiency of this technique in stallions by reducing or preventing membrane damage and cell death. The present study aimed to evaluate the effect of adding membrane stabilizers to the freezing medium and assess the quality and in vitro capacitation of stallion sperm after thawing. Semen samples from three stallions frozen with membrane stabilizers (cholesterol-loaded cyclodextrin and cholestanol-loaded cyclodextrin) were evaluated in two experiments: i) sperm quality and functional analysis after thawing, and ii) sperm quality and functional analysis after 4 h of post-thaw incubation in capacitating conditions. Plasma membrane integrity, mitochondrial membrane potential, membrane lipid disorder, intracellular Ca²⁺, tyrosine phosphorylation, acrosome reaction, DNA damage, sperm motility, and binding to the zona pellucida were assessed. The results showed that cholesterol-loaded cyclodextrin was the stabilizer that most efficiently reduced the membrane disruption and post-thaw cell damage. In addition, this stabilizer made it possible to obtain in vitro capacitated sperm showing higher plasma membrane integrity, mitochondrial membrane potential, sperm motility, binding to the zona pellucida and better response to in vitro capacitating conditions.

Developing a reproducible protocol for culturing functional confluent monolayers of differentiated equine oviduct epithelial cells

We describe the development of two methods for obtaining confluent monolayers of polarized, differentiated equine oviduct epithelial cells (EOEC) in Transwell inserts and microfluidic chips. EOECs from the ampulla were isolated post-mortem and seeded either (1) directly onto a microporous membrane as differentiated EOECs (direct seeding protocol) or (2) first cultured to a confluent de-differentiated monolayer in conventional wells, then trypsinized and seeded onto a microporous membrane (re-differentiation protocol). Maintenance or induction of EOEC differentiation in these systems was achieved by air-liquid interface introduction. Monolayers cultured via both protocols were characterized by columnar, cytokeratin 19-positive EOECs in Transwell inserts. However, only the re-differentiation protocol could be transferred successfully to the microfluidic chips. Integrity of the monolayers was confirmed by transepithelial resistance measurements, tracer flux and the demonstration of an intimate network of tight junctions. Using the direct protocol, 28% of EOECs showed secondary cilia at the apical surface in a diffuse pattern. In contrast, re-differentiated polarized EOECs rarely showed secondary cilia in either culture system (>90% of the monolayers showed <1% ciliated EOECs). Occasionally (5-10%), re-differentiated monolayers with 11-27% EOECs with secondary cilia in a diffuse pattern were obtained. Additionally, nuclear progesterone receptor expression was found to be inhibited by simulated luteal phase hormone concentrations, and sperm binding to cilia was higher for re-differentiated EOEC monolayers exposed to estrogen-progesterone concentrations mimicking the follicular rather than luteal phase. Overall, a functional equine oviduct model was established with close morphological resemblance to in vivo oviduct epithelium.

Effects of In Vitro Interactions of Oviduct Epithelial Cells with Frozen-Thawed Stallion Spermatozoa on Their Motility, Viability and Capacitation Status

Simple Summary

The use of assisted reproductive techniques, which involve the manipulation of sperm and oocytes in the laboratory, support owner production of valuable animals’ offspring. However, several limitations remain underlining the need to further optimize existing protocols as well as to develop new strategies. For example, the required conditions to make equine spermatozoa competent to fertilize an oocyte in vitro (IVF) have not been established. Therefore, our initial goal was to optimize different conditions associated with frozen equine sperm manipulations in order to improve their quality. We observed that simple factors such as sample concentration, incubation period and centrifugation time affect the sperm motility. Since in vivo fertilization involves the interaction between spermatozoa and epithelial cells in the mare’s oviductal tract, our next goal was to mimic this environment by establishing primary cultures of oviductal cells. Using this in vitro system, we were able to select a sperm population capable of fertilization. In short, this study provides a novel protocol that improves the yield of fertilization-capable sperm obtained from equine frozen spermatozoa.

Abstract

Cryopreservation by negatively affecting sperm quality decreases the efficiency of assisted reproduction techniques (ARTs). Thus, we first evaluated sperm motility at different conditions for the manipulation of equine cryopreserved spermatozoa. Higher motility was observed when spermatozoa were incubated for 30 min at 30 × 10⁶/mL compared to lower concentrations (p < 0.05) and when a short centrifugation at 200× g was performed (p < 0.05). Moreover, because sperm suitable for oocyte fertilization is released from oviduct epithelial cells (OECs), in response to the capacitation process, we established an in vitro OEC culture model to select a sperm population with potential fertilizing capacity in this species. We demonstrated E-cadherin and cytokeratin expression in cultures of OECs obtained. When sperm–OEC cocultures were performed, the attached spermatozoa were motile and presented an intact acrosome, suggesting a selection by the oviductal model. When co-cultures were incubated in capacitating conditions a greater number of alive (p < 0.05), capacitated (p < 0.05), with progressive motility (p < 0.05) and with the intact acrosome sperm population was observed (p < 0.05) suggesting that the sperm population released from OECs in vitro presents potential fertilizing capacity. Improvements in handling and selection of cryopreserved sperm would improve efficiencies in ARTs allowing the use of a population of higher-quality sperm.

The Presence of D-Penicillamine during the In Vitro Capacitation of Stallion Spermatozoa Prolongs Hyperactive-Like Motility and Allows for Sperm Selection by Thermotaxis

Assisted reproductive technologies (ARTs) in the horse still yield suboptimal results in terms of pregnancy rates. One of the reasons for this is the lack of optimal conditions for the sperm capacitation in vitro. This study assesses the use of synthetic human tubal fluid (HTF) supplemented with D-penicillamine (HTF + PEN) for the in vitro capacitation of frozen/thawed stallion spermatozoa by examining capacitation-related events over 180 min of incubation. Besides these events, we explored the in vitro capacity of the spermatozoa to migrate by thermotaxis and give rise to a population of high-quality spermatozoa. We found that HTF induced higher levels of hyperactive-like motility and protein tyrosine phosphorylation (PTP) compared to the use of a medium commonly used in this species (Whitten's). Also, HTF + PEN was able to maintain this hyperactive-like motility, otherwise lost in the absence of PEN, for 180 min, and also allowed for sperm selection by thermotaxis in vitro. Remarkably, the selected fraction was enriched in spermatozoa showing PTP along the whole flagellum and lower levels of DNA fragmentation when compared to the unselected fraction (38% ± 11% vs 4.4% ± 1.1% and 4.2% ± 0.4% vs 11% ± 2% respectively, t-test p < 0.003, n = 6). This procedure of in vitro capacitation of frozen/thawed stallion spermatozoa in HTF + PEN followed by in vitro sperm selection by thermotaxis represents a promising sperm preparation strategy for in vitro fertilization and intracytoplasmic sperm injection in this species.

Update on mammalian sperm capacitation: how much does the horse differ from other species?

In contrast to various other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. In particular, stallion spermatozoa fails to penetrate the zona pellucida, most likely due to incomplete activation of stallion spermatozoa (capacitation) under in vitro conditions. In other mammalian species, specific capacitation triggers have been described; unfortunately, none of these is able to induce full capacitation in stallion spermatozoa. Nevertheless, knowledge of capacitation pathways and their molecular triggers might improve our understanding of capacitation-related events observed in stallion sperm. When sperm cells are exposed to appropriate capacitation triggers, several molecular and biochemical changes should be induced in the sperm plasma membrane and cytoplasm. At the level of the sperm plasma membrane, (1) an increase in membrane fluidity, (2) cholesterol depletion and (3) lipid raft aggregation should occur consecutively; the cytoplasmic changes consist of protein tyrosine phosphorylation and elevated pH, cAMP and Ca2+ concentrations. These capacitation-related events enable the switch from progressive to hyperactivated motility of the sperm cells, and the induction of the acrosome reaction. These final capacitation triggers are indispensable for sperm cells to migrate through the viscous oviductal environment, penetrate the cumulus cells and zona pellucida and, finally, fuse with the oolemma. This review will focus on molecular aspects of sperm capacitation and known triggers in various mammalian species. Similarities and differences with the horse will be highlighted to improve our understanding of equine sperm capacitation/fertilizing events.

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.

Lyophilized seminal plasma can improve stallion semen freezability

The aim of this study was to evaluate the effect of lyophilized seminal plasma (LSP) on stallion semen freezability. Seminal plasma from 30 stallions was lyophilized to obtain a pool of LSP. Fifteen ejaculates from five stallions were supplemented before freezing with 0 mg/mL (Control), 1.44 mg/mL (LSP1), 5.04 mg/mL (LSP2) or 8.68 mg/ mL (LSP3) of LSP. Total antioxidant capacity (TAC) of LSP was assessed using Oxygen Radical Absorbance Capacity (ORAC) assay. Post-thaw motility and kinetics, sperm viability, normal morphology and membrane integrity were evaluated. Completely randomized mixed models were fitted for data analyses. The results was analyzed based on freezability of semen samples. TAC for LSP pool was 13679.4±911.6 μmol Trolox 100/g (ORAC units). Semen supplementation with LSP1 and LSP2 showed a positive effect on post-thaw total motility and membrane integrity. Supplementation with LSP3 showed a decrease in post-thaw total and progressive motility, straight line velocity and sperm viability. For poor freezability semen samples, supplementation with LSP1 and LSP2, showed higher post-thaw total motility and membrane integrity than good freezability semen samples. In conclusion, supplementation with LSP can improve the post-thaw seminal quality of stallion semen with poor freezability.

Melatonin reduces cAMP-stimulated capacitation of ram spermatozoa

The presence of melatonin receptors on the surface of ram spermatozoa has led to speculation about melatonin having a role in sperm functionality. The aim of this study was to elucidate the mechanism through which melatonin regulates ram sperm capacitation induced by a cocktail containing cAMP-elevating agents. Cocktail samples capacitated in the presence of 1µM melatonin showed lower percentages of capacitated spermatozoa (chlortetracycline staining; P<0.001) together with a decrease in protein tyrosine phosphorylation (P<0.01) and lower levels of reactive oxygen species (ROS) and cAMP (P<0.05) compared with cocktail samples without the hormone. Determination of kinematic parameters, together with principal component and cluster analyses, allowed us to define four sperm subpopulations (SP). After 3h of incubation with cAMP-elevating agents, the percentages of spermatozoa belonging to SP1 (high straightness) and SP4 (less-vigorous spermatozoa with non-linear motility) increased while SP2 and SP3 (rapid spermatozoa starting hyperactivation or already hyperactivated) decreased compared with the control sample. The presence of melatonin at 100 pM and 10nM restored these subpopulations to values closer to those found in the control sample. These results indicate that melatonin at micromolar concentrations modulates ram sperm capacitation induced by cAMP-elevating agents, reducing ROS and cAMP levels, whereas at lower concentrations melatonin modifies motile sperm subpopulations. These findings warrant further studies on the potential use of melatonin for controlling capacitation in artificial insemination procedures.

Stage-specific metabolomic changes in equine oviductal fluid: New insights into the equine fertilization environment

A repeatable protocol for equine in vitro fertilization (IVF) has remained elusive. This is likely, in part, due to suboptimal composition of capacitation or IVF media that are currently in use. Hence, we aimed to analyse the metabolome of equine oviductal fluid (OF) at the pre- (PRE) and immediate post-ovulatory (PST) stages using proton magnetic resonance spectroscopy (¹H NMR). Oviductal fluid from eight PRE and six PST mares were used to prepare a total of five samples per group. A total of 18 metabolites were identified. The five metabolites with the highest concentrations in the OF samples were lactate, myoinositol, creatine, alanine and carnitine. Only fumarate and glycine showed significant differences in their concentrations between PRE and PST OF samples, with higher concentrations in the PST samples. In a preliminary study, stallion spermatozoa (n = 3 ejaculates) were incubated with different concentrations of PST OF from one mare (0, 0.0625, 0.125, 0.25, 0.5 or 1%; v:v). After 4 h of sperm incubation, protein tyrosine phosphorylation (PY) by western blotting, sperm motility, and acrosomal status were evaluated. An increase of PY was observed in sperm from two stallions when treated with 0.0625% and 0.125% of OF; however no change in PY was noted in the other stallion. There were no effects of OF on spermatozoa motility or acrosome status. These results provide the first information on the metabolomics of equine OF at different stages of the estrus cycle, and present the possibility that OF may affect PY in stallion spermatozoa.

pH-dependent effects of procaine on equine gamete activation†

Procaine directly triggers pH-dependent cytokinesis in equine oocytes and induces hypermotility in stallion spermatozoa, an important event during capacitation. However, procaine-induced hyperactivated motility is abolished when sperm is washed to remove the procaine prior to sperm-oocyte co-incubation. To understand how procaine exerts its effects, the external Ca2+ and Na+ and weak base activity dependency of procaine-induced hyperactivation in stallion spermatozoa was assessed using computer-assisted sperm analysis. Percoll-washed stallion spermatozoa exposed to Ca2+-depleted (+2 mM EGTA) procaine-supplemented capacitating medium (CM) still demonstrated hyperactivated motility, whereas CM without NaCl or Na+ did not. Both procaine and NH4Cl, another weak base, were shown to trigger a cytoplasmic pH increase (BCECF-acetoxymethyl (AM)), which is primarily induced by a pH rise in acidic cell organelles (Lysosensor green dnd-189), accompanied by hypermotility in stallion sperm. As for procaine, 25 mM NH4Cl also induced oocyte cytokinesis. Interestingly, hyperactivated motility was reliably induced by 2.5-10 mM procaine, whereas a significant cytoplasmic cAMP increase and tail-associated protein tyrosine phosphorylation were only observed at 10 mM. Moreover, 25 mM NH4Cl did not support the latter capacitation characteristics. Additionally, cAMP levels were more than 10× higher in boar than stallion sperm incubated under similar capacitating conditions. Finally, stallion sperm preincubated with 10 mM procaine did not fertilize equine oocytes. In conclusion, 10 mM procaine causes a cytoplasmic and acidic sperm cell organelle pH rise that simultaneously induces hyperactivated motility, increased levels of cAMP and tail-associated protein tyrosine phosphorylation in stallion spermatozoa. However, procaine-induced hypermotility is independent of the cAMP/protein tyrosine phosphorylation pathway.

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.

Analysis of the equine "cumulome" reveals major metabolic aberrations after maturation in vitro

Background

Maturation of oocytes under in vitro conditions (IVM) results in impaired developmental competence compared to oocytes matured in vivo. As oocytes are closely coupled to their cumulus complex, elucidating aberrations in cumulus metabolism in vitro is important to bridge the gap towards more physiological maturation conditions. The aim of this study was to analyze the equine “cumulome” in a novel combination of proteomic (nano-HPLC MS/MS) and metabolomic (UPLC-nanoESI-MS) profiling of single cumulus complexes of metaphase II oocytes matured either in vivo (n = 8) or in vitro (n = 7).

Results

A total of 1811 quantifiable proteins and 906 metabolic compounds were identified. The proteome contained 216 differentially expressed proteins (p ≤ 0.05; FC ≥ 2; 95 decreased and 121 increased in vitro), and the metabolome contained 108 metabolites with significantly different abundance (p ≤ 0.05; FC ≥ 2; 24 decreased and 84 increased in vitro). The in vitro “cumulome” was summarized in the following 10 metabolic groups (containing 78 proteins and 21 metabolites): (1) oxygen supply, (2) glucose metabolism, (3) fatty acid metabolism, (4) oxidative phosphorylation, (5) amino acid metabolism, (6) purine and pyrimidine metabolism, (7) steroid metabolism, (8) extracellular matrix, (9) complement cascade and (10) coagulation cascade. The KEGG pathway “complement and coagulation cascades” (ID4610; n = 21) was significantly overrepresented after in vitro maturation. The findings indicate that the in vitro condition especially affects central metabolism and extracellular matrix composition. Important candidates for the metabolic group oxygen supply were underrepresented after maturation in vitro. Additionally, a shift towards glycolysis was detected in glucose metabolism. Therefore, under in vitro conditions, cumulus cells seem to preferentially consume excess available glucose to meet their energy requirements. Proteins involved in biosynthetic processes for fatty acids, cholesterol, amino acids, and purines exhibited higher abundances after maturation in vitro.

Conclusion

This study revealed the marked impact of maturation conditions on the “cumulome” of individual cumulus oocyte complexes. Under the studied in vitro milieu, cumulus cells seem to compensate for a lack of important substrates by shifting to aerobic glycolysis. These findings will help to adapt culture media towards more physiological conditions for oocyte maturation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5836-5) contains supplementary material, which is available to authorized users.

Effect of cumulus cell removal and sperm pre-incubation with progesterone on in vitro fertilization of equine gametes in the presence of oviductal fluid or cells

In spite of many attempts to establish an in vitro fertilization (IVF) technique in the equine, no efficient conventional IVF technique is available. The presence of oviductal fluid or oviductal cells during IVF helps to improve embryo production in vitro but is not sufficient to reach high fertilization rates. Thus, our aim was to perform equine IVF either after sperm pre-incubation with oviductal fluid or in the presence of oviductal cells, and to evaluate the effect of cumulus removal from the oocyte or sperm pre-incubation with progesterone. In experiments 1 and 2, IVF was performed in the presence of porcine oviduct epithelial cells. The removal of cumulus cells from equine oocytes after in vitro maturation tended to increase the percentage of fertilization when fresh sperm was used (1/33 vs. 4/31, p > 0.05) but had no effect when frozen sperm was used (1/32 vs. 1/32). Equine sperm pre-incubation with progesterone did not significantly influence the fertilization rate when fresh or frozen sperm was used (2/14 vs. 2/18 for fresh, 1/29 vs. 1/25 for frozen). In experiments 3 and 4, IVF was performed after pre-incubation of sperm with porcine oviductal fluid. The removal of cumulus cells tended to increase the percentage of fertilization when fresh sperm was used (1/24 vs. 3/26, p > 0.05). Sperm pre-incubation with progesterone did not significantly influence the fertilization rate when fresh or frozen sperm was used (2/39 vs. 2/36 for fresh, 2/37 vs. 1/46 for frozen), but two 3-4 cell stage zygotes were obtained with fresh sperm pre-incubated with progesterone. This is an encouraging result for the setting up of an efficient IVF procedure in equine.

Novel methods to detect capacitation-related changes in spermatozoa

Prior to interaction with the oocyte, spermatozoa must undergo capacitation, which involves a series of physio-chemical transformations that occur in the female tract. As capacitation is a pre-requisite for successful fertilisation, it is a topic of great interest for sperm biologists, but the complexity of the numerous biochemical and biophysical processes involved make it difficult to measure. Capacitation is an extremely complex event that encompasses numerous integrated processes that can occur concurrently during this window of time. The identification of techniques to accurately assess and quantify capacitation is therefore crucial to gain a meaningful insight into this fascinating sperm maturation event. Whilst there are extensive reviews in the literature that focus on the functional changes to spermatozoa during capacitation, few have examined the methods required to measure these changes. The aim of this review is to highlight frequently used methods to quantify different stages of capacitation and identify promising novel techniques. Factors that are able to modulate various capacitation processes will also be discussed. The overall outcome is to provide researchers with a toolbox of methods that can be used to gain a deeper understanding of the intricacies of capacitation in spermatozoa.

Effects of lidocaine on equine ejaculated sperm and epididymal sperm post-castration

In equids, it is common to inject lidocaine into the testicles at the time of routine castration to provide analgesia. The effects of lidocaine on equine sperm have not been evaluated in vitro or on epididymal sperm collected following castration. The aims of this study were to determine effects of clinically relevant doses of lidocaine on equine spermatozoa in vitro using freshly collected semen and to compare the characteristics of epididymal spermatozoa after routine castration with or without intra-testicular lidocaine administration. We hypothesized that increasing concentrations of lidocaine would decrease total motility (TM), progressive motility (PM), velocity of the average path (VAP), velocity of the curved line (VCL), linearity (LIN), normal morphology (M) and membrane integrity (MI). We also hypothesized that injection of intra-testicular lidocaine would decrease TM, PM, VAP, VCL, LIN, M, and MI following routine castration, epididymal flushing and cryopreservation. In experiment 1, sperm was collected from four stallions and mixed with lidocaine at concentrations of 1 μg/ml, 10 μg/ml, 100 μg/ml, 1,000 μg/ml and 10,000 μg/ml. M and MI were compared to the control sample at 0 and 48 h. Motility parameters were analyzed at 0, 2, 4, 6, 24, and 48 h. In experiment 2, 12 stallions were castrated under general anesthesia. One testicle was removed without the use of intra-testicular lidocaine and the other testicle was removed 10 min after injection of 10 ml of 2% lidocaine. Results: In experiment 1, fresh sperm showed no significant difference (p < 0.05) compared to control at either 1 μg/ml or 10 μg/ml concentrations of lidocaine. There were significant decreases in PM, VAP, VCL, and LIN at concentrations of 100μg/ml-10,000 μg/ml and for TM at lidocaine concentrations of 1,000-10,000 μg/ml compared to control. Morphology did not change at any lidocaine concentration. Membrane integrity decreased significantly at 10,000 μg/ml lidocaine. In the second experiment 1.03 ± 0.42 μg/ml lidocaine was detected in the epididymal flush of stallions treated with lidocaine. There were no significant differences in any measured parameters between the control and the lidocaine treated testicles. Intra-testicular lidocaine injection at the time of castration did not affect any measured parameters after epididymal flush. Lidocaine concentrations higher than 100 μg/ml in-vitro resulted in decreased motility parameters of the spermatozoa independent of exposure time.

Hyperactivated stallion spermatozoa fail to exhibit a rheotaxis-like behaviour, unlike other species

The journey of spermatozoa through the female genital tract is facilitated by rheotaxis, or the cell's preference to swim against a flow, as well as thigmotaxis, the wall tracking behaviour, which guides them to the site of fertilisation. The aim of this study was to characterise the rheotactic and thigmotactic response of stallion sperm within a microfluidic channel. Stallion sperm rheotaxis was assessed within the microfluidic channel with regard to: (i) A range of flow velocities, (ii) Varying media viscosity and (iii) Sperm hyperactivation. Sperm distribution across the microfluidic channel was also studied and compared to human and ram sperm. Stallion sperm progressed furthest at a velocity range of 10-30 µm/s, with an optimum velocity of 20 µm/s. A flow viscosity of 2.5cP or greater reduced sperm rheotaxis (P < 0.05). Stallion sperm that were hyperactivated were unable to exhibit rheotaxis within the microfluidic channel, whereas, both hyperactivated human and ram sperm did exhibit positive rheotaxis under the same conditions. The number of sperm swimming near the microfluidic channel walls was higher than in the microfluidic channel centre (P < 0.05). This is the first study to illustrate that stallion sperm are rheotactically responsive and increasing viscosity reduces this response. We also demonstrated that sperm are predominantly inclined to swim along a surface and uniquely, hyperactivated stallion sperm are non-progressive and do not exhibit a rheotactic response unlike other species.

Effects of a micronutrient supplementation combined with a phosphodiesterase type 5 inhibitor on sperm quantitative and qualitative parameters, percentage of mature spermatozoa and sperm capacity to undergo hyperactivation: A randomised controlled trial

The main objective of this study was to evaluate the effects of a micronutrient supplementation (MS) combined with avanafil on sperm function. Oligoasthenospermic men (n = 217) were treated daily for 90 days with either an MS (45 men, Group A), l-carnitine (44 men, Group B), MS plus avanafil (43 men, Group C) or avanafil (43 men, Group D); another group of 42 men with oligoasthenospermia (Group E) received no treatment. Sperm parameters were evaluated before and after the end of treatment in each Group A, B, C and D respectively. The same sperm parameters were measured in each participant of Group E before and at the 90-day experimental period. Within Groups A, C or D, the total percentage of motile spermatozoa, the hypoosmotic swelling test (HOST) result and the percentage of hyperactivated spermatozoa after incubation under conditions known to induce sperm capacitation were significantly greater after MS or MS plus avanafil treatment, or avanafil treatment than before the respective treatment. We suggest that MS or MS plus avanafil combined administration or avanafil alone improves sperm membrane permeability with an overall result improvement in sperm motility, outcome of HOST and increase in the percentage of hyperactivated spermatozoa.

CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC

To fertilize an egg, sperm must reside in the female reproductive tract to undergo several maturational changes that are collectively referred to as capacitation. From a molecular point of view, the HCO₃^--dependent activation of the atypical soluble adenylyl cyclase (ADCY10) is one of the first events that occurs during capacitation and leads to the subsequent cAMP-dependent activation of protein kinase A (PKA). Capacitation is also accompanied by hyperpolarization of the sperm plasma membrane. We previously reported that PKA activation is necessary for CFTR (cystic fibrosis transmembrane conductance regulator channel) activity and for the modulation of membrane potential (Em). However, the main HCO₃^- transporters involved in the initial transport and the PKA-dependent Em changes are not well known nor characterized. Here, we analyzed how the activity of CFTR regulates Em during capacitation and examined its relationship with an electrogenic Na⁺/HCO₃^- cotransporter (NBC) and epithelial Na⁺ channels (ENaCs). We observed that inhibition of both CFTR and NBC decreased HCO₃^- influx, resulting in lower PKA activity, and that events downstream of the cAMP activation of PKA are essential for the regulation of Em. Addition of a permeable cAMP analog partially rescued the inhibitory effects caused by these inhibitors. HCO₃^- also produced a rapid membrane hyperpolarization mediated by ENaC channels, which contribute to the regulation of Em during capacitation. Altogether, we demonstrate for the first time, that NBC cotransporters and ENaC channels are essential in the CFTR-dependent activation of the cAMP/PKA signaling pathway and Em regulation during human sperm capacitation.

Characterization of extracellular Ca2+ -dependent full-type hyperactivation in ejaculated boar spermatozoa preincubated with a cAMP analog

Ejaculated boar spermatozoa exhibit two types of hyperactivation: full and non-full. Full-type hyperactivation is characterized by the asymmetrical bending of the entire middle piece-principal piece and a twisting/figure-eight-like trajectory, and can be induced by simple incubation with CaCl₂ after preincubation with a cAMP analog (Sp-5,6-dichloro-1-β-D-ribofuranosyl-benzimidazole-3',5'-cyclic monophosphorothioate [cBiMPS]). Here, we compared the sperm flagellar motility after treatments with elevators of [Ca²⁺ ]_i (cBiMPS/CaCl₂ , thimerosal, procaine, and 4-aminopyridine) to characterize the regulatory mechanism of extracellular Ca²⁺ -dependent, full-type hyperactivation in ejaculated boar spermatozoa, and examined the possible involvement of Transient receptor potential cation channel subfamily C member 3 (TRPC3) in this event using the specific inhibitor Pyr3. Full-type hyperactivation was induced by a 60-min incubation with CaCl₂ following a 180-min preincubation with cBiMPS but without Ca²⁺ . Thimerosal-treated spermatozoa exhibited full-type hyperactivation in a manner independent of extracellular Ca²⁺ ; conversely, this was not observed in procaine- or 4-aminopyridine-treated spermatozoa. A 20-min treatment with Pyr3 between preincubation with cBiMPS and incubation with CaCl₂ , significantly suppressed the normal phenotype. These observations indicated that mechanisms underlying full-type hyperactivation in spermatozoa incubated with CaCl₂ after preincubation with cBiMPS are different from those in the thimerosal-treated spermatozoa. Furthermore, indirect immunofluorescence localized TRPC3 in the upper segment of the middle piece, which bends asymmetrically during full-type hyperactivation but not in non-full-type hyperactivation, suggesting that TRPC3 may be involved in the extracellular Ca²⁺ -dependent full-type hyperactivation in ejaculated boar spermatozoa.

Exposure to follicular fluid during oocyte maturation and oviductal fluid during post-maturation does not improve in vitro embryo production in the horse

Most wild equids and many domestic horse breeds are at risk of extinction, so there is an urgent need for genome resource banking. Embryos cryopreservation allows the preservation of genetics from male and female and is the fastest method to restore a breed. In the equine, embryo production in vitro would allow the production of several embryos per cycle. Intracytoplasmic sperm injection (ICSI) is used to generate horse embryos, but it requires expensive equipment and expertise in micromanipulation, and blastocyst development rates remain low. No conventional in vitro fertilization (IVF) technique for equine embryo production is available. The development of culture conditions able to mimic the maturation of the oocyte in preovulatory follicular fluid (pFF) and the post-maturation in oviductal fluid (OF) may improve embryo production in vitro. Our aim was to analyse the effect of in vitro maturation in pFF and incubation in OF on in vitro maturation of equine oocytes, fertilization using conventional IVF or ICSI, and embryo development after culture in synthetic oviductal fluid (SOF) or DMEM-F12. Oocytes collected from slaughtered mares or by ovum pick up were matured in vitro in pFF or semi-synthetic maturation medium (MM). The in vitro maturation, fertilization and development rates were not statistically different between pFF and MM. After in vitro maturation, oocytes were incubated with or without OF. Post-maturation in OF did not significantly improve the fertilization and development rates. Thus, in our study, exposure to physiological fluids for oocyte maturation and post-maturation does not improve in vitro embryo production in the horse.

Stallion Sperm Cryopreservation Using Various Permeating Agents: Interplay Between Concentration and Cooling Rate

In this study, modeling and experimental approaches were used to investigate the interplay between cooling rate and protectant concentration for cryopreservation of stallion sperm. Glycerol (GLY), ethylene glycol (EG), dimethylformamide (DMF), propylene glycol (PG), and dimethyl sulfoxide (DMSO) were tested as cryoprotective agents (CPAs), using concentrations up to 1500 mM and cooling rates ranging from 5°C to 55°C min^-1. Modeling of the extent of sperm dehydration during freezing was done using previously determined values of the sperm membrane permeability to water to predict optimal cooling rates for cryopreservation. Sperm cryosurvival was experimentally determined through flow cytometric assessments on membrane intactness and using computer-assisted analysis of motility. Sperm could withstand exposure to 1500 mM concentrations prefreeze for all CPAs tested. The overall highest cryosurvival rates were obtained with DMF, followed by GLY and EG, whereas the use of PG and DMSO resulted in poor cryosurvival rates. Cryosurvival with DMF increased with increasing concentration, reaching a plateau at 500 mM, whereas for GLY and EG, an optimum concentration between 250 and 500 mM resulted in maximal survival. An optimal cooling rate was only observed at low CPA concentrations, whereas at higher concentrations, cryosurvival rates were not affected by the cooling rate. In the case of DMF, survival remained relatively high in the investigated range of concentrations and cooling rates, whereas with GLY and EG, a much narrower combination of CPA concentration and cooling rate resulted in optimal cryosurvival. Sperm cryopreserved with DMF showed altered motility characteristics indicating hyperactivation, which was not observed with GLY and EG. Optimal cooling rates that were predicted from calculated dehydration curves did not match experimentally determined optimal cooling rates.

Pronuclear formation by ICSI using chemically activated ovine oocytes and zona pellucida bound sperm

Background

In order to improve ICSI, appropiate sperm selection and oocyte activation is necessary. The objective of the present study was to determine the efficiency of fertilization using ICSI with chemically activated ovine oocytes and sperm selected by swim up (SU) or swim up + zona pellucida (SU + ZP) binding.

Results

Experiment 1, 4–20 replicates with total 821 in vitro matured oocytes were chemically activated with ethanol, calcium ionophore or ionomycin, to determine oocyte activation (precense of one PN). Treatments showed similar results (54, 47, 42 %, respectively) but statistically differents (P < 0.05) than mechanical activated oocytes in sham, ICSI and sham injection (13, 25, 32 %, respectively) (10–17 replicates; n = 429).

Experiment 2: Twelve ejaculates and 28 straws of semen were used (11–19 replicates). Sperm were selected by SU in BSA-TCM 199-H medium. A total of 2,294 fresh sperm and 2,760 from frozen-thawed semen were analyzed after SU or SU + ZP binding. Fresh sperm selected by SU showed acrosome reaction (AR) of 59 %, the sperm selected by SU + ZP binding increased AR to 91 %. In comparison, the AR of frozen-thawed sperm using SU or SU + ZP binding was 77 and 86 %, respectively (P < 0.05).

Experiment 3: fertilization in 200 mechanical activativated oocytes (17 replicates) was 4 %, but fertilization increased in ethanol activated oocytes after ICSI (12-28 %) (5–6 replicates). When fresh sperm only selected by SU were injected to 123 oocytes, a fertilization rate (28 %) was achieved; in sperm selected by SU + ZP was 25 % (73 oocytes). In comparison, in frozen-thawed sperm selected by SU, fertilization was 13 % (70 oocytes), whereas sperm from SU + ZP binding displayed 12 % (51 oocytes) (P > 0.05).

Conclusions

Chemical activation induces higher ovine oocyte activation than mechanical activation. Ethanol slightly displays higher oocyte activation than calcium ionophore and ionomicine. Sperm selection with SU + ZP increased AR/A and AR/D rates in comparison with SU in fresh and frozen-thawed sperm. According to this, in terms of fertilization rates, chemical activation after ICSI increased oocyte PN formation compared to mechanical activation. Also, fresh sperm treated with SU and SU + ZP were significantly different than frozen-thawed sperm, but between sperm treatments no significant differences were obtained.

Why doesn't conventional IVF work in the horse? The equine oviduct as a microenvironment for capacitation/fertilization

In contrast to man and many other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. The apparent inability of stallion spermatozoa to penetrate the zona pellucida in vitro is most likely due to incomplete activation of spermatozoa (capacitation) because of inadequate capacitating or fertilizing media. In vivo, the oviduct and its secretions provide a microenvironment that does reliably support and regulate interaction between the gametes. This review focuses on equine sperm-oviduct interaction. Equine sperm-oviduct binding appears to be more complex than the presumed species-specific calcium-dependent lectin binding phenomenon; unfortunately, the nature of the interaction is not understood. Various capacitation-related events are induced to regulate sperm release from the oviduct epithelium and most data suggest that exposure to oviduct secretions triggers sperm capacitation in vivo However, only limited information is available about equine oviduct secreted factors, and few have been identified. Another aspect of equine oviduct physiology relevant to capacitation is acid-base balance. In vitro, it has been demonstrated that stallion spermatozoa show tail-associated protein tyrosine phosphorylation after binding to oviduct epithelial cells containing alkaline secretory granules. In response to alkaline follicular fluid preparations (pH 7.9), stallion spermatozoa also show tail-associated protein tyrosine phosphorylation, hyperactivated motility and (limited) release from oviduct epithelial binding. However, these 'capacitating conditions' are not able to induce the acrosome reaction and fertilization. In conclusion, developing a defined capacitating medium to support successful equine IVF will depend on identifying as yet uncharacterized capacitation triggers present in the oviduct.

A journey through people, places, and projects in equine assisted reproduction

A research study is a product of not only a question and its pursuit but also the people, places, and facilities available at the time. My work in equine assisted reproduction has progressed from embryo transfer to oocyte maturation, oocyte transfer, intracytoplasmic sperm injection, embryo biopsy, embryo vitrification, and cloning, as a result of collaborations with an array of remarkable people. This is a summary of some of the stories behind the studies.

An alkaline follicular fluid fraction induces capacitation and limited release of oviduct epithelium-bound stallion sperm

Induction of hyperactivated motility is considered essential for triggering the release of oviduct-bound mammalian spermatozoa in preparation for fertilization. In this study, oviduct-bound stallion spermatozoa were exposed for 2 h to: i) pre-ovulatory and ii) post-ovulatory oviductal fluid; iii) 100% and iv) 10% follicular fluid (FF); v) cumulus cells, vi) mature equine oocytes, vii) capacitating and viii) non-capacitating medium. None of these triggered sperm release or hyperactivated motility. Interestingly, native FF was detrimental to sperm viability, an effect that was negated by heat inactivation, charcoal treatment and 30 kDa filtration alone or in combination. Moreover, sperm suspensions exposed to treated FF at pH 7.9 but not pH 7.4 showed Ca(2+)-dependent hypermotility. Fluo-4 AM staining of sperm showed elevated cytoplasmic Ca(2+) in hyperactivated stallion spermatozoa exposed to treated FF at pH 7.9 compared to a modest response in defined capacitating conditions at pH 7.9 and no response in treated FF at pH 7.4. Moreover, 1 h incubation in alkaline, treated FF induced protein tyrosine phosphorylation in 20% of spermatozoa. None of the conditions tested induced widespread release of sperm pre-bound to oviduct epithelium. However, the hyperactivating conditions did induce release of 70-120 spermatozoa per oviduct explant, of which 48% showed protein tyrosine phosphorylation and all were acrosome-intact, but capable of acrosomal exocytosis in response to calcium ionophore. We conclude that, in the presence of elevated pH and extracellular Ca(2+), a heat-resistant, hydrophilic, <30 kDa component of FF can trigger protein tyrosine phosphorylation, elevated cytoplasmic Ca(2+) and hyperactivated motility in stallion sperm, but infrequent release of sperm pre-bound to oviduct epithelium.

The future of computer-aided sperm analysis

Computer-aided sperm analysis (CASA) technology was developed in the late 1980s for analyzing sperm movement characteristics or kinematics and has been highly successful in enabling this field of research. CASA has also been used with great success for measuring semen characteristics such as sperm concentration and proportions of progressive motility in many animal species, including wide application in domesticated animal production laboratories and reproductive toxicology. However, attempts to use CASA for human clinical semen analysis have largely met with poor success due to the inherent difficulties presented by many human semen samples caused by sperm clumping and heavy background debris that, until now, have precluded accurate digital image analysis. The authors review the improved capabilities of two modern CASA platforms (Hamilton Thorne CASA-II and Microptic SCA6) and consider their current and future applications with particular reference to directing our focus towards using this technology to assess functional rather than simple descriptive characteristics of spermatozoa. Specific requirements for validating CASA technology as a semi-automated system for human semen analysis are also provided, with particular reference to the accuracy and uncertainty of measurement expected of a robust medical laboratory test for implementation in clinical laboratories operating according to modern accreditation standards.

Effects of α-tocopherol and freezing rates on the quality and heterologous in vitro fertilization capacity of stallion sperm after cryopreservation

The effects of supplementation of α-tocopherol and different freezing rates (FRs) on the ability of stallion sperm to fertilize bovine oocytes with intact zona pellucida were investigated, in an attempt to develop a model to assess cryopreserved sperm function. Semen was obtained from four purebred Lusitano stallions (n = 4). Each ejaculate was subjected to cryopreservation with a commercial extender (Ghent, Minitub Iberia, Spain), without any supplementation (control) or supplemented with 2-mM α-tocopherol. The semen was exposed to two different FRs between 5 °C and -15 °C: slow (5 °C/min) and moderate (10 °C/min). After thawing, the viability (SYBR®-14 and propidium iodide [PI]), mitochondrial membrane potential (JC-1, 5,5',6,6'-tetrachloro-1,1',3,3'tetraethylbenzimidazolyl carbocyanine iodine) and membrane lipid peroxidation (C11-BODIPY(581/591)) of each sample were determined by flow cytometry. Moreover, the heterologous IVF rate was measured to evaluate the fertilization capacity of postthaw semen in the four different treatments. For both extenders, the viability was higher for spermatozoa cooled slowly (39.40 ± 2.17 vs. 17.59 ± 2.25-control; 31.96 ± 2.19 vs. 11.46 ± 1.34-Tocopherol; P < 0.05). The α-tocopherol extender improved (P < 0.05) postthaw lipid peroxidation (10.28 ± 0.70 vs. 15.40 ± 0.95-slow FR; 10.14 ± 0.40 vs. 13.48 ± 0.34-moderate FR); however, it did not improve viability and mitochondrial membrane potential. Regarding the IVF rate, in the moderate FR, α-tocopherol supplementation reported a higher percentage of IVF (20.50 ± 2.11; P < 0.05), comparing with the control (14.00 ± 1.84). Regarding the slow FR, no significance differences were observed for percentage of IVF between the two extenders and the FRs. However, it seems that the α-tocopherol supplementation improved the IVF rate. In conclusion, this research reported that bovine oocytes intact zona pellucida can be used to evaluate the quality of postthaw stallion semen and α-tocopherol supplementation in the stallion freezing extender might exert a protective effect against oxidative damage during heterologous IVF.