Stallion sperm freezing with sucrose extenders: A strategy to avoid permeable cryoprotectants

Freezing Stallion Semen-What Do We Need to Focus on for the Future?

Artificial insemination (AI) is used frequently in the breeding of sport horses, apart from Thoroughbreds. Most AIs are carried out with cooled semen rather than frozen semen because of the difficulties in identifying a protocol that is suitable for freezing most ejaculates and the necessity to inseminate close to ovulation because of the short life of the thawed spermatozoa. More widespread use of frozen semen would improve biosecurity, allow greater choice of stallions, and offer more flexibility when managing deliveries of semen to the stud. It would even decrease the amount of antibiotics used in semen extenders, since the volume of frozen semen is smaller than when cooled semen is inseminated. However, there is considerable variability in the cryosurvival of spermatozoa from different stallions, leading to the classification of stallions as good or bad freezers. Improvements could be made at the level of stallion nutrition, the semen collection regimen, the extender, the removal of seminal plasma, and the cooling protocol, among others. Stallion sperm membranes are highly susceptible to lipid peroxidation, but research on antioxidants has failed to identify an additive that would benefit all stallions. In the future, biomarkers for sperm freezability could be used as an aid in identifying suitable ejaculates for cryopreservation.

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

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

Effects of egg yolk level, penetrating cryoprotectant, and pre-freeze cooling rate, on the post-thaw quality of stallion sperm

The current study determined the effect of the egg-yolk (phospholipid source) level (egg yolk [20% EY] vs. skim-milk + egg yolk [SM + 2% EY]), cryoprotectant (glycerol [Gly] vs. glycerol + methylformamide [Gly + MF]), and pre-freeze cooling rate (-0.1 vs. -1 vs. -5 °C/min) on post-thaw stallion sperm quality. In Experiment 1, ejaculates (n = 27) from 9 stallions (3 ejaculates each) with varied sperm quality (High, Average, or Low) were frozen in EY-Gly, SMEY-Gly, EY-Gly + MF, or SMEY-Gly + MF extenders. Sperm in each group were cooled from 22° to 5°C using either -0.1 °C/min or -1 °C/min linear cooling rates prior to freezing. In Experiment 2, ejaculates (n = 24) from 12 stallions (2 ejaculates each) with High or Average sperm quality were frozen in EY-Gly, EY-Gly + MF, or in BotuCrio (BC) extenders. Sperm in each group were cooled from 22° to 5°C using either -1 or -5 °C/min linear cooling rates prior to freezing. In Experiment 1, for stallions with High or Average sperm quality, either cooling rate generally resulted in lower sperm quality for the SMEY-based extenders than for the EY-based extenders (P < 0.05). Stallions with Low sperm quality were unaffected by any experimental treatment (P > 0.05). In Experiment 2, a -5 °C/min cooling rate yielded lower sperm quality in BC than in EY-Gly or EY-Gly + MF groups (P < 0.05); however, a -1 °C/min cooling rate yielded similar sperm quality among these treatments (P > 0.05). In summary, the phospholipid level in the freezing extender and the pre-freeze cooling rate, but not the penetrating cryoprotectant, affected the post-thaw quality of stallion sperm.

Cryopreservation of Semen in Domestic Animals: A Review of Current Challenges, Applications, and Prospective Strategies

Cryopreservation is a way to preserve germplasm with applications in agriculture, biotechnology, and conservation of endangered animals. Cryopreservation has been available for over a century, yet, using current methods, only around 50% of spermatozoa retain their viability after cryopreservation. This loss is associated with damage to different sperm components including the plasma membrane, nucleus, mitochondria, proteins, mRNAs, and microRNAs. To mitigate this damage, conventional strategies use chemical additives that include classical cryoprotectants such as glycerol, as well as antioxidants, fatty acids, sugars, amino acids, and membrane stabilizers. However, clearly current protocols do not prevent all damage. This may be due to the imperfect function of antioxidants and the probable conversion of media components to more toxic forms during cryopreservation.

Diluent Containing Dimethylformamide Added With Sucrose Improves In Vitro Quality After Freezing/Thawing Stallion Sperm

The aim of this study was to investigate the effects of sucrose on post-thawed equine semen quality. Semen samples (n = 24) were collected from six stallions. They were diluted (200 × 10⁶ sperm/mL) in a freezing medium based on skimmed milk, egg yolk, dimethylformamide, and supplemented with sucrose at concentrations of 0 (Control), 25, 50, and 100 mM and in a commercial extender (BotuCrio). Subsequently, they were filled in straws (0.5 mL) and subjected to freezing and storage (-196°C). Immediately after thawing (37°C, 30 seconds), semen samples were evaluated for kinetics (CASA), plasma and acrosomal membrane integrity, and mitochondrial membrane potential (flow cytometry). The addition of 50 and 100mM sucrose to the freezing extender increased (P < .05) the parameters of TM, PM, VCL, VSL, and VAP, compared to the control group. The WOB parameter of the group supplemented with 100 mM sucrose was higher (P < .05) than the control group. Higher values ​​(P < .05) of ALH and BCF were observed in groups treated with sucrose (25, 50, and 100 mM), compared to BotuCrio. The semen frozen in the presence of 100 mM sucrose presented higher percentages (P < .05) of sperm with intact plasma and acrosomal membranes, and high mitochondrial membrane potential in relation to the other groups. It is concluded that the addition of sucrose to equine semen freezing extender increase motility (50 and 100 mM), plasma and acrosomal membrane integrity preserve, and high sperm mitochondrial membrane potential (100 mM) after thawing.

A review of methods for preserving male fertility

Male infertility is responsible for 50% of men's health problems and has always been a concern for personal and social issues. A survey of global statistics suggests an increase in infertility rate as one of the critical issues documented in studies. There are different ways of maintaining fertility in men, depending on their age. In this paper, we review the preservation methods used for fertility treatment in Iran and other countries. Available data were reviewed from Google Scholar, PubMed, Scopus, Web of Science, IranMedex, MEDLIB, IranDoc and Scientific Information Database and searched for articles published up to 2018, using the medical subject heading (MeSH) terms for cryopreservation, sperm, testicular, spermatogonia stem cell, male infertility and/or Iranian and in the world, to provide evidence from evaluation of fertility preservation the methods. Based the search strategy, 274 manuscripts were found. After reviewing the titles, abstracts and manuscripts in their entirety, 119 articles were obtained and selected according to the eligibility criteria. The 85 studies mentioned above were divided into three categories (sperm, testis, and spermatogonia stem cells (SSCs)), and methods of fertility preservation were investigated. Ways to maintain male fertility were different depending on age, and included sperm, testicular, and SSC freezing. The number of studies on testicular tissue and SSCs was low for human samples, and more studies are still needed. Sperm freezing at infertility centres is the top for male fertility preservation.

A preliminary study on the effects of E-Z Mixin® and EquiPlus® extenders supplemented with Edible Bird's Nest on the quality of chilled Arabian stallion semen

The aim of this study was to evaluate the effects of adding different concentrations of edible bird’s nest (EBN) which is secreted by swiftlet birds (Aerodramus fuciphagus), into EquiPlus® and E-Z Mixin® extenders on the quality of chilled Arabian stallion semen at various storage times (0, 24 and 48 h). Ten ejaculates were collected from five stallions, and diluted using the two extenders containing 0% (control), 0.12%, 0.24% and 0.24% of EBN + seminal plasma (SP). All the diluted semen samples were then cooled and stored at 5 °C, and examined at 0, 24 and 48 h. Sperm kinetic parameters were assessed using computer assisted sperm analysis (CASA) and viability were assessed using Hoechst33342/PI stain. In both extenders, total motility (TM) and progressive motility (PM) were significantly higher at 0.12% and 0.24% compared to 0.24% + SP at 24 and 48 h. At 0.12%, E-Z mixin® treated semen had significantly higher TM and PM than EquiPlus^® at 24 and 48 h. At 0.12% and 0.24%, average path velocity (VAP), straight-line velocity (VSL) and curvilinear velocity (VCL) were significantly higher in E-Z mixin® treated semen compared to EquiPlus^® at 24 and 48 h. Comparisons between the two extender types at different concentrations of EBN showed no significant difference in lateral head amplitude (ALH), linearity (LIN), straightness (STR), beat cross frequency (BCF) and viability, irrespective of the storage time. The percentage of viable was significantly higher in E-Z mixin® than EquiPlus® at 0 and 48 h in control and 0.12%. Supplementation of the E-Z mixin^® extender with 0.12% and 0.24% EBN concentrations in the absence of SP provided better CASA parameters such as TM, PM, VAP, VSL, and VCL at 24 and 48 h storage time. In conclusion, the results of this study indicated that chilled semen from Arabian stallion that was extended using E-Z mixin® and supplemented with 0.12% and 0.24% EBN concentrations performed better and yielded superior results in sperm kinetic parameters and % viable compared to EquiPlus® at 24 and 48 h storage time.

Fertilizing capacity of vitrified stallion sperm assessed utilizing heterologous IVF after different semen warming procedures

The aim of this study was to evaluate the fertilizing capacity of frozen or vitrified stallion sperm after assessing different warming procedures. In Experiment 1, different warming procedures were compared after sperm vitrification: immersion in extender at 43 °C (C), or in a water bath at 37 °C/30 s (W37), 43 °C/10 s (W43) or 60 °C/5 s (W60). With the W60 treatment, there were greater values (P < 0.05) for VCL (83.93 ± 3.6 μm/s) and ALH (3.00 ± 0.2 μm) than freezing and with the C group, and greater values (P < 0.001) for PM (35.33 ± 2.5 %) than with the W43 treatment. In Experiment 2, the fertilizing capacity of vitrified and frozen sperm was assessed utilizing heterologous IVF procedures, using cattle oocytes. Vitrification resulted in greater values (P < 0.05) than freezing for the number of bound sperm (1.36 ± 0.3 and 0.69 ± 0.2, respectively). There were no differences between frozen or vitrified sperm in pronuclear formation (26 hours post-insemination - hpi; 14.08 ± 4.2 % and 22.78 ± 4.8 %, respectively) or cleavage rate (32.77 ± 4.3 % and 39.66 ± 4.6 %, respectively). In conclusion, vitrified stallion sperm warmed in a water bath at 60 ºC had the capacity to penetrate cattle oocytes, leading to pronuclear formation and hybrid embryo cleavage after heterologous IVF.

Vitrification of Donkey Sperm: Is It Better Using Permeable Cryoprotectants?

Simple Summary

Conventional donkey sperm-freezing using permeable cryoprotectants has been successfully performed, and good sperm parameters have been obtained after thawing. Unfortunately, artificial insemination of jennies with cryopreserved semen has given unsatisfactory results. Vitrification by directly dropping the sperm into the liquid nitrogen following the spheres methodology has been developed in human beings as an alternative to conventional freezing. This technique has shown to be a species-specific methodology and the concentration of cryoprotectants should be optimized in donkeys. Additionally, in this study, a permeable cryoprotectant (glycerol) has been tested for the first time for donkey sperm vitrification. According to our findings, vitrification of donkey sperm was effectively carried out using an extender supplemented with sucrose or bovine serum albumin (BSA) as non-permeable agent. When glycerol, a permeable agent, was compared to sucrose 0.1 M and BSA 5%, sperm quality significantly decreased. Therefore, donkey sperm vitrification in the absence of permeable agents obtained better results and gives a new approach to create a pattern for future studies of fertility trials.

Abstract

Vitrification by direct exposure of sperm to liquid nitrogen is increasing in popularity as an alternative to conventional freezing. In this study, the effect of permeable cryoprotectant agents for donkey sperm vitrification was compared to an extender containing non-permeable cryoprotectants. First, three different concentrations of sucrose (0.1, 0.2, and 0.3 molar, M) and bovine serum albumin, BSA (1, 5, and 10%) were compared. Secondly, the concentration of non-permeable agents producing the most desirable results was compared to an extender containing glycerol as permeable agent. Vitrification was performed by dropping 30 μL of sperm suspension directly into LN2 and warming at 42 °C. Sperm motility (total, TM; and progressive, PM) and plasma membrane integrity, PMI (mean ± SEM) were statistically compared between treatments. Sucrose 0.1 M showed a significantly higher percentage of total sperm motility (21.67 ± 9.22%) than sucrose 0.2 M (14.16 ± 4.50%) and 0.3 M (8.58 ± 6.22%); and no differences were found in comparison to the control (19.71 ± 10.16%). Vitrification with sucrose 0.1 M or BSA 5% obtained similar results for TM (21.67 ± 9.22% vs. 19.93 ± 9.93%), PM (13.42 ± 6.85% vs. 12.54 ± 6.37%) and PMI (40.90 ± 13.51% vs. 37.09 ± 14.28); but both showed higher percentages than glycerol (TM = 9.71 ± 4.19%; PM = 5.47 ± 3.17%; PMI = 28.48 ± 15.55%). In conclusion, donkey sperm vitrification in spheres using non-permeable cryoprotectants exhibited better sperm motility and viability parameters after warming than sperm vitrification using extenders containing permeable cryoprotectants.

Is sperm cryopreservation in absence of permeable cryoprotectants suitable for subfertile donkeys?

Sperm from fertile donkeys have been successfully frozen in absence of permeable cryoprotectants. The aim of this study was to determine whether this cryopreservation method is suitable for subfertile donkeys in comparison to conventional sperm freezing with glycerol. Ejaculates were collected from four Andalusian Donkeys: three fertile and one subfertile. Semen was frozen with an extender containing glycerol (GLY), or adding instead sucrose 0.25 molar and 1% bovine serum albumin (SUC) as non-permeable cryoprotectants. After thawing, samples were assessed for total (TM, %) and progressive (PM, %) sperm motility by CASA, plasma membrane integrity (PMI, %) by epifluorescence microscopy and DNA integrity (DFI, %) by SCSA. Results (mean ± SD) were compared between extenders in fertile and subfertile donkeys using the Student's t test. No differences between GLY and SUC treatments were found in the fertile group for the sperm parameters assessed. In subfertile donkey ejaculates, GLY resulted in significantly higher values than SUC for TM (25.5 ± 3.1 vs. 19.6 ± 1.9) and PM (13.3 ± 5.1 vs. 4.0 ± 1.2), respectively. In conclusion, considering all the sperm parameters assessed, sperm freezing in absence of permeable cryoprotectants may not be still an option for cryopreservation of subfertile donkey sperm.

Seasonal variations in sperm DNA fragmentation and pregnancy rates obtained after artificial insemination with cooled-stored stallion sperm throughout the breeding season (spring and summer)

The aim of this study was to assess seasonal variations during different periods of the breeding season (spring and summer) on stallion sperm DNA fragmentation and in vivo fertility associated with cooled-stored semen samples. Ejaculates were collected from eleven stallions and assessed for sperm motility (assessed by computer-assisted sperm analysis) and plasma membrane integrity (evaluated under fluorescence microscopy). Sperm DNA fragmentation (evaluated by the Sperm Chromatin Dispersion test) was assessed in cooled-stored semen at 5 °C for up to 24 h. Artificial insemination was performed throughout the breeding season. Mares were inseminated with cooled-stored semen (up to 24 h) every other day until ovulation. Pregnancy rates per cycle were determined detecting the embryonic vesicle by ultrasonography fifteen days after ovulation. Values (mean ± SD) for progressive sperm motility were significantly higher (P < 0.05) in spring (53.57 ± 9.97%) in comparison to summer (41.37 ± 10.81%). No significant differences in plasma membrane integrity were found between seasons (P > 0.05). Sperm DNA fragmentation was significantly lower (P < 0.01) in spring in comparison to summer after 0h (4.81 ± 1.87% vs. 8.77 ± 5.78%), 6h (9.00 ± 3.19% vs. 18.73 ± 8.22%) and 24h (14.6 ± 4.13% vs. 30.14 ± 9.85%) of cooled-storage. Pregnancy rates per cycle were also significantly higher (P < 0.01) in spring (50%) in comparison to summer (37%). There was a moderate negative relationship between positive pregnancies and sperm with fragmented DNA (r = - 0.619; P < 0.001). Semen samples associated with moderate fertility levels (Pregnancy rate < 50%) showed a higher percentage of sperm with fragmented DNA compared to samples obtaining higher fertility levels. In conclusion, seasonal variations were found during the breeding season, obtaining lower sperm DNA fragmentation and higher pregnancy rates in spring. Additionally, samples with the highest proportion of sperm with fragmented DNA showed the lowest fertility levels throughout the breeding season.

Knockout serum replacement is an efficient serum substitute for cryopreservation of human spermatozoa

The freeze-thaw procedure causes irreversible structural and functional changes in human spermatozoa. In order to decrease the detrimental effects of cryopreservation and improve the quality of post-thawed spermatozoa, the constituents of the freezing solution attracted considerable attention. In this study, for the first time, we evaluated the efficacy of knockout serum replacement (KSR) as a substitute for human serum albumin (HSA) for cryopreservation of human spermatozoa. Twenty semen samples were collected from normozoospermic men and divided them into five equal groups. One of the aliquots was diluted with glycerol-based medium as a control group (CON). The other four aliquots were diluted with the sucrose solution containing 5% HSA (H5), 10% HSA (H10), 5% KSR (K5), and 10% KSR (K10). The diluted samples were frozen and preserved in liquid nitrogen. Post thawed sperm parameters including motion characteristics, viability, membrane integrity, mitochondrial activity, acrosome integrity and DNA intactness in all of the sucrose-based groups were comparable with glycerol-based medium. The replacement of HSA by 10% KSR in the freezing medium resulted in significantly higher post-thawed viability, acrosome integrity and DNA intactness compared with other sucrose-based groups. In conclusion, the addition of 10% KSR to the sucrose-based freezing solution improves the quality of post-thawed human spermatozoa and may have potential to develop chemically defined freezing medium.

Ejaculated compared with epididymal stallion sperm vitrification

The aim of this study was to evaluate the effect of trehalose and lactose extenders on ejaculated and epididymal stallion sperm vitrification. Ejaculated semen samples were collected from seven fertile stallions, and cauda epididymis samples were collected from ten stallion carcasses after slaughter. Both the ejaculated and the epididymis samples were diluted and vitrified using INRA 96® and bovine serum albumin as well as trehalose or lactose. As a control, ejaculated and epididymal samples were collected and frozen using the conventional method. Vitrification was performed by immersing sperm suspensions directly in LN2. After thawing or devitrification, there was assessment of samples for sperm motility using computer-assisted analysis. Viability was assessed using SYBR-14 and propidium iodide (PI) and acrosome integrity by fluorescein using isothiocyanate combined with peanut agglutinin (FITC-PNA) and PI. Epididymal sperm vitrification with trehalose (EPT) or lactose (EPL) resulted in greater progressive sperm motility than sperm of the control sample (EPC). After post-thaw/devitrification of sperm in the EPT group, sperm motility was greater (P<0.001) compared to that using EPL (50.72 ± 5.09% compared with 34.21 ± 3.02%). The results from assessment of ejaculated sperm samples after undergoing the vitrification process indicated cells were less viable (P<0.001) than the control (EJC) sample. In conclusion, vitrification of epididymal stallion sperm using trehalose might be a beneficial alternative for the long-term storage of sperm samples with great economic value. Spermatozoa from vitrified ejaculates of stallions, however, had lesser motility and viability rates than samples subjected to conventional freezing.

Cryopreservation of Andalusian donkey (Equus asinus) spermatozoa: Use of alternative energy sources in the freezing extender affects post-thaw sperm motility patterns but not DNA stability

The aim of this study was to compare the effect of three sugars and Equex paste in a freezing extender for donkey sperm cryopreservation. Ejaculates (n = 18) were collected from six Andalusian donkeys of proven fertility were pooled (two ejaculates per pool) and cryopreserved using a freezing extender containing three different sugars (glucose, fructose and sorbitol), with or without the addition of Equex paste. Sperm quality was assessed before and after freezing-thawing for motility, morphology, plasma membrane integrity, acrosome integrity and DNA integrity. The use of sorbitol in the freezing extender improved total and progressive sperm motility (P < 0.05) and amplitude of lateral head displacement (P < 0.01), but it reduced the values for other sperm motility variables compared with glucose (P < 0.001). The use of fructose resulted in a reduction in values for most CASA variables (P < 0.05), whereas addition of Equex paste did not have any beneficial effect on values for these variables (P > 0.05). Glucose was more effective in maintaining sperm morphology (P < 0.05), while there was no beneficial effect with the addition of Equex paste (P > 0.05). Supplementation of fructose and Equex paste in the freezing extender decreased plasma membrane integrity (P < 0.05) as compared with glucose, but there were no differences between treatments for acrosome and DNA integrity (P > 0.05), even after 24 h of incubation. The use of different sugar sources in the extender could affect the in vitro post-thaw quality of cryopreserved donkey spermatozoa, with sorbitol being an interesting alternative for improving the sperm quality. Results of the present study indicate the use of Equex paste could negatively affect post-thaw outcomes for sperm viability in this species.

Vitrification of stallion sperm using 0.25 ml straws: Effect of volume, concentration and carbohydrates (sucrose/trehalose/raffinose)

Sperm vitrification is a rapid freezing method in which carbohydrates are used as cryoprotectants. The aim of this study was to determine the optimal volume, concentration and type of carbohydrates for stallion sperm vitrification using 0.25 ml straws in comparison to conventional freezing. Ejaculates (n = 54) were collected from six stallions. For vitrification, straws were filled with different volumes (30, 70, 100 μl), sperm concentrations (50, 100, 200 × 10⁶ sperm/ml) and extenders containing sucrose (20, 100, 200 mM), trehalose (50, 100, 200 mM) and raffinose (50, 100, 200 mM) and plunged into LN₂. Conventional freezing was performed in 0.5 ml straws frozen in LN₂ vapors. Sperm motility, plasma and acrosome membrane integrities and DNA fragmentation were compared among treatments. The use of straws filled with 100 μl at 100 × 10⁶ sperm/ml with the extender containing 100 mM trehalose resulted in greater values for sperm quality than the other concentrations, volumes and carbohydrates. With vitrification, there were greater values (mean ± SEM; P < 0.05) than freezing for progressive motility (48.2 ± 2.3 compared with 37.3 ± 2.2%), plasma membrane integrity (82.8 ± 1.5 compared with 74.1 ± 1.9%), and intact acrosomes (50.2 ±  1.2 compared with 43.1 ± 1.4%); and less DNA fragmentation (6.4 ± 0.7 compared with 8.2 ± 0.3%). In conclusion, stallion sperm can be vitrified in 0.25 ml straws filled with 100 μl of sperm at 100 x 10⁶ sperm/ml using an extender with 100 mM of trehalose, obtaining better sperm quality after warming than conventional freezing.

Optimization of donkey sperm vitrification: Effect of sucrose, sperm concentration, volume and package (0.25 and 0.5 mL straws)

The aim of this study was to assess the effect of different factors affecting vitrification success of donkey sperm: extender, sperm concentration, volume and storage vessel type. In Experiment 1, sucrose supplementations at 0.25 and 0.1 M were compared using two base extenders (containing or not egg-yolk); in Experiment 2, three sperm concentrations were assessed: 100, 200 or 300 million sperm/mL; and in Experiment 3, three different sperm volumes (100, 160 and 200 μL) and two different storage vessels (0.25 and 0.5 mL straws) were assessed. Sperm motility variables (CASA), plasma membrane and acrosome (evaluated under fluorescence microscopy) and sperm DNA integrity (flow cytometry) were evaluated after warming with comparisons of protocols. There was a greater total (55.7 ± 16.4%) and progressive (44.0 ± 11.5%) motility using the extender with egg-yolk and 0.1 M sucrose. There were no effects of sperm concentrations on vitrification results (P > 0.05). The 0.25 mL covered straw showed higher values than the 0.5 mL straw for total (50.0 ± 17.3% vs 2.0 ± 6.7%) and progressive (40.5 ± 14.9% vs 0.9 ± 1.5%) motility, plasma membrane (43.9 ± 14.4% vs 14.0 ± 16.4%) and acrosome integrity (51.5 ± 13.6% vs 28.0 ± 14.7%), respectively. In conclusion, values for donkey sperm quality variables after vitrification were greater using an extender containing egg-yolk and 0.1 M sucrose, at 300 million sperm/mL in 0.25 mL straws with outer covers.

Vitrification of Large Volumes of Stallion Sperm in Comparison With Spheres and Conventional Freezing: Effect of Warming Procedures and Sperm Selection

Stallion sperm was vitrified using straws in comparison with spheres and conventional freezing. Vitrification was performed plunging 30 μL of sperm (spheres) or 0.5 mL straws into liquid nitrogen (LN₂) and conventional freezing using 0.5 mL straws frozen in LN₂ vapors. Sperm vitrified in straws were submitted to different warming procedures (42°C/20 seconds; 60°C/15 seconds) and single-layer centrifugation (SLC). Total (TM, %) and progressive sperm motility (PM, %), plasma membrane (IMS, %) and acrosome integrity (AIS, %) were statistically compared between treatments (mean ± SEM). Significant higher values (P < .001) were obtained after vitrification using spheres in comparison with conventional freezing and vitrification in straws for TM (54.46 ± 3.2 vs. 36.47 ± 3.2 vs. 2.50 ± 1.2, %), PM (38.63 ± 3.4 vs. 15.11 ± 2.0 vs. 1.9 ± 0.9, %), IMS (65.40 ± 2.8 vs. 50.50 ± 2.8 vs. 21.63 ± 2.1, %), and AIS (48.89 ± 2.8 vs. 15.46 ± 1.7 vs. 4.69 ± 0.9, %). No differences were found between warming procedures. Single-layer centrifugation after warming at 42°C/20 seconds obtained higher values (P < .05) than unselected samples for TM (32.52 ± 5.8%), PM (14.22 ± 2.8%), IMS (60.01 ± 3.2%), and AIS (44.5 ± 2.2%), whereas selection after 60°C/15 seconds increased TM (23.11 ± 4.3%) and IMS (67.11 ± 3.9%). In conclusion, vitrification in spheres obtained better sperm quality than conventional freezing and vitrification in straws. Warming procedures did not affect the sperm quality but SLC could be a strategy to enhance the quality of the samples after sperm vitrification using 0.5 mL straws.

Influence of Different Combinations of Permeable and Nonpermeable Cryoprotectants on the Freezing Capacity of Equine Sperm

This study was aimed to evaluate the effect of permeable cryoprotectants in combination with trehalose or sucrose on the freezing capacity of stallion sperm. For this purpose, the ejaculates (n = 24) were collected from four healthy mature Turkmen stallions. The ejaculates were pooled and diluted with one of the extenders containing a combination of 5% of permeating (dimethylacetamide [DMA]; dimethylformamide [DMF] or glycerol) and 50 mM of nonpermeating cryoprotectant agents (CPAs) (sucrose or trehalose) to a final concentration of 200 × 10⁶ spermatozoa/mL. The extended samples were cryopreserved and thawed using a standard protocol. The samples were evaluated for motion kinetics, morphological abnormalities, plasma membrane functionality (PMF), viability, and lipid peroxidation. The results showed that the sperm cryopreserved in extender containing DMA produced higher (P ≤ .05) total motility, straightness, straight line velocity, curvilinear velocity, and lower (P ≤ .05) lipid peroxidation (malondialdehyde [MDA] concentration) compared with DMF and glycerol groups. Overall, both DMA and DMF have shown higher (P ≤ .05) sperm motion kinetics, viability, PMF, and lower (P ≤ .05) morphological abnormalities and MDA concentration compared with the glycerol. However, except morphological abnormalities, all of the other parameters did not differ between trehalose and sucrose. Likewise, there was no interaction between permeating and nonpermeating CPAs (P ≥ .05) except in terms of sperm abnormalities (P ≤ .05). In conclusion, the use of DMA or DMF as alternative CPAs of glycerol could be more effective for successful cryopreservation of stallion sperm. The nonsignificant interaction between permeating and nonpermeating CPAs for most of the post-thaw sperm parameters negates possible synergism among these compounds.