Cryopreservation of bull semen: Evolution from egg yolk based to soybean based extenders

Effect of autologous platelet-rich plasma on the fertility and quality of cryopreserved buffalo bull semen: a comparative study using OptiXcell® and tris egg yolk extenders

BACKGROUND

Buffalo spermatozoa have a distinct membrane structure that makes them more vulnerable to cryopreservation, resulting in lower-quality post-thawed sperm. This decreases the success rate of artificial insemination in buffaloes. Understanding and addressing these specific vulnerabilities are essential for improving reproductive techniques in buffalo populations. The properties of cryopreserved buffalo bull semen were examined in this study regarding the impact of adding autologous platelet-rich plasma (PRP) to OptiXcell® or Tris egg yolk-based extenders. Ten buffalo bulls were used to collect semen. Each bull's ejaculate was separated into two main equal amounts, each of which was then diluted with either OptiXcell® or Tris egg yolk-based extender, supplemented with various PRP concentrations (5%, 10%, and 15%), and the control (0%), before being cryopreserved according to established protocols. Following equilibration and thawing, the quality and functionality of the sperm were evaluated, along with the antioxidant enzyme activities (GSH and TAC), malondialdehyde (MDA) content, and in vivo fertilization rate of the thawed semen.

RESULTS

All PRP concentrations in both extenders, particularly 10% PRP, improved the quality and functionality of the sperm in both equilibrated and frozen-thawed semen. Additionally, the antioxidant enzyme activities in both extenders were higher in the PRP-supplemented groups compared to the control group in thawed semen (P < 0.05). All post-thaw sperm quality, antioxidant enzyme activities, and functionality aside from DNA integrity were higher (P < 0.05) in the PRP-supplemented OptiXcell® than in the PRP-supplemented Tris egg yolk-based extender. The fertility of cryopreserved semen in the extenders supplemented with 10% and 15% PRP increased (P < 0.05) significantly more than that of the control extenders, with 10% PRP being the optimum concentration in OptiXcell® (80%) compared to that of Tris egg yolk-based extender (66.67%) and control of two extenders (53.33% and 46.67%, respectively).

CONCLUSIONS

Even though autologous PRP-supplemented extenders have a protective impact on equilibrated and cryopreserved semen, 10% PRP-supplemented OptiXcell® extenders are more effective at preserving post-thaw semen quality, functionality, and antioxidant capacity, which increases the in vivo fertility of buffalo bulls.

Evaluation of equine semen frozen in extenders free of egg yolk using two different freezing curves

A chemically defined cryopreservation extender that maintains seminal parameters is relevant. Fifteen ejaculates from 5 stallions (n= 5; r=3) were diluted in 5 extenders: 1) EDTA-glucose based extender with egg-yolk and dimethylformamide (EY); 2) commercial equine extender (CE); 3) CE with dimethylformamide (CE-3); 4) bovine commercial extender with liposomes (OP); 5) bovine commercial extender with soybean lecithin (BIO), and frozen using a slow and a rapid temperature descent curve. Post-thaw evaluations were: sperm kinematic parameters, viability and acrosome status, membrane lipoperoxidation and DNA fragmentation. Sperm data were analysed using an ANOVA or Friedman test (results mean ± SD). Paired comparison between the two freezing curves was analysed using the Wilcoxon test. Total and progressive motility were significantly higher (P<0.05) in the EY and CE-3 samples using the slow curve, whereas for the fast curve, total and progressive motility were significantly higher (P<0.05) in the EY samples compared to all the extenders and the samples frozen in CE-3 were significantly higher than the remaining extenders (P<0.05). The percentages of live acrosome intact sperm and of live non-peroxidized sperm were significantly higher (P<0.05) in the EY extender when using either of the freezing curves and in turn, were significantly higher (P<0.05) in samples frozen in CE-3 compared to the remaining extenders. Intact DNA was significantly lower (P<0.05) in the BIO extender, using the rapid curve. To conclude, the commercial equine extender with 3% dimethylformamide, without egg-yolk, could be a suitable alternative for extenders with egg-yolk.

A longer period of epididymal sperm interaction with extender components during cryopreservation improves sperm quality, decreases the size of sperm distal cytoplasmic droplets, and changes the number of nanoparticles in the extender

While cryopreservation of cauda epididymal sperm (SpCau) allows the preservation of post-mortem bulls' gametes, the process triggers sperm damage. Although improving post-thaw sperm quality, using egg yolk extenders (EY) raises biosafety concerns which forces the use of EY-free extenders (EYFE). Since EYFE are less efficient in preserving post-thaw sperm quality, a strategy for ejaculated sperm (SpEj) frozen with EYFE is to add an Equilibrium Time (ET) step period to the cryopreservation process. However, the ET effect on the quality of SpCau cryopreserved in EYFE remains unknown. Distinct from SpEJ, SpCau physiologically displays cytoplasmic droplets (CDs) in the flagellum that may benefit cell exchange during ET. We hypothesized that using ET in SpCau cryopreserved with EYFE impacts sperm morphofunctional features, CD area, and in vitro fertility ability. Extender nanoparticles were also assessed. Following collection from the cauda epididymis of six Nellore bulls by retrograde flow, SpCau were cryopreserved in EYFE BoviFree® (Minitube, Germany) using three ET protocols: ET0 (no-ET); ET2.5 (2.5 h-ET); and ET5 (5 h-ET). SpCau from ET2.5 and ET5 showed a higher (P ≤ 0.05) percentage of motility and integrity of plasma and acrosome membranes and a smaller (P ≤ 0.05) distal CD area. There are no differences in sperm abnormalities, oxidative stress, capacitation-like events, and in vitro fertility ability. However, a better sperm recovery was found after Percoll® selection for ET2.5 and ET5. Interestingly, the number of nanoparticles in the extender decreased in post-thawed samples. In conclusion, an ET of 2.5 or 5 h is required for an efficient SpCau cryopreservation using an EYFE.

Sesame oil as a partial substitute for egg yolk in goat semen extenders

This study aimed to evaluate the effects of replacing egg yolk extender with sesame oil on the quality of sperm in goats following incubation at 37°C, chilling at 4°C, and freezing. Semen samples were collected from four intact male goats. The individual semen sample was divided into six groups consisting of a control group and five treatment groups with different egg yolk-to-sesame oil ratios. Seminal plasma was removed, and the sperm pellet was diluted with experimental semen extenders. The control group contained an extender of 10 % egg yolk (SO0), and the experimental extenders were composed of 8.75 % egg yolk and 1.25 % sesame oil (SO1.25); 7.5 % egg yolk and 2.5 % sesame oil (SO2.5); 5 % egg yolk and 5 % sesame oil (SO5); 2.5 % egg yolk and 7.5 % sesame oil (SO7.5); and 10 % sesame oil (SO10). Each group of semen was divided into three groups, incubated at 37°C for 1 h, chilled at 4°C for 4 h, or frozen for 24 h. Five replicates were performed. Sperm quality was evaluated, including motility, viability, and functional membrane integrity. The SO1.25 group achieved the highest sperm quality rate among the treatment groups, and the extender did not have a negative effect compared to the control. However, the total replacement of egg yolk with sesame oil in an extender resulted in the lowest sperm quality. In conclusion, the ratios of egg yolk and sesame oil that were acceptable for goat semen cryopreservation were 8.75 % and 1.25 %, respectively.

Cryopreserving Rabbit Semen: Impact of Varying Sperm Concentrations on Quality and the Standardization of Protocol

This study aimed to investigate the impact of sperm concentrations on the in vitro quality of cryopreserved rabbit semen. The semen pools (n = 8, from 80 donors) were split into five aliquots with final sperm concentrations of 15, 25, 35, 55, and 75 × 106 per straw. The sperm motility parameters (CASA system) and membrane integrity (flow cytometric analysis) were both evaluated at various stages of the cryopreservation process: fresh semen dilution, cooling, equilibration, and immediately after and 30 min post-thawing. The results indicated the significant influence of the sperm concentration on the total motility (TM) and progressive motility (PM), with a consistent decline in all sperm variables over the time points. Notably, the semen with a final concentration of 15 × 106 exhibited a higher TM and PM after cooling and equilibration. The post-thawing quality (TM, PM) was higher (p < 0.05) in the mid-range sperm concentrations of 25 × 106 (49.9% and 19.7%) and 35 × 106 (46.2% and 19.7%) compared to the other concentrations. This study demonstrated that the sperm concentration per straw played a significant role in specific phases of the cryopreservation process. These findings contribute valuable insights for refining and standardizing the cryopreservation protocol for rabbit semen, emphasizing the importance of the sperm concentration.

The Effects of Glycerophospholipid Nanomicelles on the Cryotolerance of Frozen-Thawed Rooster Sperm

Semen banking is an efficient method of artificial insemination for commercial breeders. However, the cryopreservation process induces severe damages to plasma membranes, which leads to reduced fertility potential of thawed sperm. The replacement of membrane lipids with oxidized membrane lipids repairs the cell membrane and improves its stability. The aim of this study was to investigate the effects of glycerophospholipid (GPL) nanomicelles on the cryosurvival of thawed rooster semen. Semen samples were collected from six 29-week Ross broiler breeder roosters, then mixed and divided into five equal parts. The samples were diluted with the Beltsville extender containing different concentrations of GPL according to the following groups: 0 (GPL-0), 0.1% (GPL-0.1), 0.5% (GPL-0.5), 1% (GPL-1), and 1.5% (GPL-1.5), then diluted semen was gradually cooled to 4°C during 3 hours and stored in liquid nitrogen. The optimum concentration of GPL was determined based on the quality parameters of thawed sperm. Our results showed sperm exposed to GPL-1 had significantly increased motion parameters and mitochondrial activity. The percentages of viability and membrane integrity were significantly higher in the GPL-1, and GPL-1.5 groups compared with the other groups (p < 0.05). Moreover, the lowest rate of apoptosis and lipid peroxidation were observed in the GPL-1 and GPL-1.5 groups in comparison with the frozen control group. Our findings indicated that membrane lipid replacement with GPL nanomicelles (1% and 1.5%) could substitute for damaged lipids in membranes and protect sperm cells against cryoinjury.

Morphometric features, seminal profile and diluters effect on post-thaw semen quality of Munshiganj cattle in Bangladesh

The study investigates morphometric features, seminal profile and post-thaw semen quality of Munshiganj cattle. Morphometric features were measured using measuring tape from 20 Munshiganj cattle while coat color was measured by observing in naked eye. Fresh and post thaw semen quality parameters were analyzed using Computer Assisted semen analyzer (CASA). Coat color of Munshiganj male cattle were creamy white to dull pinkish and female were white to creamy. The mean body weight, body length, hearth girth, height at wither, head length, head width, ear length, ear width, fore leg length, hind leg length, tail length, tail doc circumference, horn length, horn diameter and mouth circumference were 362.80 kg, 137.31 cm, 160.66 cm, 135.21 cm, 50.97 cm, 20.58 cm, 19.75 cm, 9.88 cm, 73.02 cm, 74.84 cm, 106.10 cm, 20.75 cm, 13.60 cm, 16.12 cm and 43.00 cm, respectively. There was significant difference (p < 0.05) between male and female in terms of body weight (418.00 vs 307.60 kg), heart girth (173.74 vs 147.57 cm), head width (22.50 vs 18.67 cm), horn diameter (18.58 vs 13.66 cm) and mouth circumference (46.60 vs 39.40 cm). Average scrotal length was 16.76 cm while scrotal circumference was 32.70 cm. Age had significant effect (p < 0.05) on morphometric characteristics of Munshiganj male and female cattle. On the other hand, season had no significant effect on semen quality. Mean semen volume, sperm concentration, total motile, progressive, static, slow and live spermatozoa were 5.83 ± 0.88 ml, 1510.27 ± 844.07 million/ml, 91.9 ± 2.17 %, 63.80 ± 12.53 %, 8.10 ± 2.17 %, 0.10 ± 0.10 %, 91.38 ± 0.25 %, respectively. On the other hand, sperm head length and width, sperm tail length of Munshiganj cattle were 10.39 ± 0.16 μm, 4.26 ± 0.07 μm, 21.5 ± 0.52 μm, respectively. Individual breeding bull had a significant (p < 0.05) effect on post-thawed motile sperm percentage. Four different diluters (Triladyl, Steridyl, Tris-egg yolk-Citrate and Andromed) were used to compare the effects of diluter on post-thaw semen quality of Munshiganj cattle and found that diluter had no significant effect (p > 0.05) on post thaw semen quality except slow motility and proximal droplet percentages. Munshiganj cattle had a distinctive phenotypic feature with standard quality semen and had no effect of egg yolk free and egg yolk based diluters on post thaw semen quality.

Fluorescent enzyme-based biosensor for sensitive analysis of DNA damage in cryopreserved sperm

The freeze-thaw process can induce irreversible structural and functional changes in human sperm, particularly sperm DNA damage. Selecting a more accurate and sensitive detection method for evaluating sperm DNA integrity is crucial. To accurately assess sperm DNA integrity following the freeze-thaw process and significantly improve the clinical and scientific utilization of cryopreserved sperm. In this study, we utilized a novel fluorescent biosensor, assisted by terminal deoxynucleotidyl transferase (TdT) and Endonuclease IV, to detect DNA breakpoints during sperm cryopreservation. We evaluated the biosensor's performance by comparing it with the conventional DNA fragmentation index (DFI) measured using sperm chromatin structure analysis (SCSA). The cryopreserved group exhibited a significantly higher sperm DFI compared to the fresh group. No significant difference was observed between the antioxidant group and the cryopreserved group. However, the new method revealed a significant reduction in the number of DNA breakpoints in the antioxidant group compared to the cryopreserved group. The novel biosensor demonstrated superior accuracy and effectiveness in assessing sperm DNA integrity during cryopreservation compared to the conventional SCSA method. We believe that the biosensor holds significant potential for widespread use in the field of reproductive medicine.

Post-Thaw Parameters of Buck Semen Quality after Soy Lecithin Extender Supplementation with Fumaric Acid

The supplementation of cryopreservation media with antioxidants improves the post-thaw quality and fertilizing ability of spermatozoa. To maximize the fertility of frozen-thawed buck spermatozoa, further research is required to overcome obstacles that have yielded controversial results and standardize protocols. In the present work, the effect of adding fumaric acid (a well-described antioxidant) to a soy lecithin semen extender on certain quality parameters of spermatozoa following freezing and thawing was examined for the first time. Five sexually mature Skopelos bucks were used, and ejaculates were collected with an artificial vagina. The semen samples (98 samples, five replicates) were diluted (400 × 106 spermatozoa/mL) with OviXcell®, supplemented with fumaric acid (0 mM, 2.15 mM, 10 mM or 30 mM), equilibrated (5 °C; 3 h), packed (0.5 mL straws), frozen and stored (-196 °C) until further processing. After thawing, the spermatozoa total and progressive motility (CASA), viability (eosin-nigrosin), membrane functional integrity (HOST), acrosome integrity (SpermBlue®) and mitochondrial function (Rhodamine-123/SYBR-14/PI) were evaluated. Statistical analysis was performed with one-way ANOVA, followed by Duncan's test; significance was set at 0.05. The addition of 2.15 mM fumaric acid improved (p < 0.05) spermatozoa viability, membrane functional integrity, acrosome integrity and mitochondrial function compared to all other concentrations. The addition of 30 mM fumaric acid decreased (p < 0.05) spermatozoa viability and mitochondrial function compared to all other concentrations. These results indicate a beneficial effect of a 2.15 mM fumaric acid addition to a soy lecithin extender on post-thaw buck spermatozoa quality. Further research is required to evaluate the in vivo fertility of frozen-thawed buck spermatozoa treated with fumaric acid, as well as to elucidate the mechanism of action of fumaric acid in spermatozoa.

Canine sperm vitrification with nonpermeable cryoprotectants and coconut water extender

This study was aimed to assess the efficiency of coconut water extender with addition of soy lecithin and sucrose as nonpermeable cryoprotectants for canine semen vitrification, using a simple method that yields a high survival rate of spermatozoa for clinical use. Twelve ejaculates from 12 adult normozoospermic dogs were collected separately by digital manipulation and only the second semen fraction was used in this study. After evaluation of volume, concentration, viability, total and progressive motility, velocity parameters and morphology, semen was diluted with a coconut water extender (50% (v/v(volume per volume)) coconut water, 25% (v/v) distilled water and 25% (v/v) 5% anhydrous monosodium citrate solution) with addition of soy lecithin and fructose at 1% and 0.25M sucrose until final concentration of 100x10⁶ spermatozoa/ml. After equilibration at 5ºC for 60 minutes, semen was vitrified by "direct dropping method" into liquid nitrogen in spheres with a volume of 30 μl. After a week of storage the spheres were devitrified as three of them were dropped into 0.5 mL of CaniPlus AI medium (Minitüb, Germany), which was previously warmed in a water bath at 42ºC for 2 minutes and evaluated about the above mentioned parameters. It was found that vitrification resulted in a lower percentage of viable sperms, normal morphology, total and progressive motilities (p<0.05), but most of velocity parameters (VCL, VSL, VAP, LIN, ALH and BCF) did not differ (p>0.05) compared to fresh semen samples. In conclusion, our results demonstrate that vitrification with coconut water extender with addition of 1% soy lecithin and 0.25M sucrose as cryoprotectants, has an excellent potential for routine canine sperm cryopreservation.

Human sperm parameter improvement associated with Ceratonia siliqua extract as a cryopreservation supplement after vitrification

OBJECTIVE

Given the destructive effects of oxidative stress on sperm structure, this study was conducted to investigate the antioxidant effects of different concentrations of Ceratonia siliqua plant extract on human sperm parameters after the freezing-thawing process.

METHODS

A total of 20 normozoospermic samples were frozen. Each sample was divided into two control groups (fresh and cryopreservation) and three cryopreservation experimental groups (containing C. siliqua extract at concentrations of 20, 30, and 40 μg/mL in the freezing extender). Motility, intracellular levels of reactive oxygen species (ROS), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), viability, and acrosome reaction parameters were evaluated.

RESULTS

Statistical analysis showed that the highest motility, viability, and PMI were associated with the 20 μg/mL concentration of C. siliqua extract. At all concentrations, intracellular ROS levels were significantly lower and the levels of MMP and the acrosome reaction were significantly higher than in the cryopreservation control group (p≤0.05).

CONCLUSION

C. siliqua extract supplements at concentrations of 20, 30, and 40 μg/mL improved sperm motility, viability, PMI, MMP, intracellular ROS, and the acrosome reaction.

Effect of modified CEP-3 diluents with aqueous soybean extract on liquid semen quality in Ongole crossbred bull

Background and Aim

Egg yolk (EY) is commonly used as an extracellular cryoprotectant in semen diluents but has some negative effects. Therefore, this study aimed to assess the potential of lecithin derived from plants, such as soybeans, as an alternative extracellular cryoprotectant and to characterize liquid semen quality of Ongole crossbred bulls using a modified caudal epididymis plasma-3 [CEP-3 (m)] as a base diluent and aqueous soybean extract (ASE).

Materials and Methods

A bull with progressive motility (PM) of fresh semen >70% was used. Two soybean extracts were also used, namely, ASE 1 and ASE 2, obtained by extraction procedures 1 and 2, respectively. The study was conducted using an experimental design with 11 treatments and ten replications, with diluents comprising different levels of ASE 1 and ASE 2, as well as a positive control with 10% EY. The parameters measured were motility (M) and its kinetic parameters, including PM, M, velocity curve linear, velocity straight linear, velocity average pathway, linearity, straightness, wobble, amplitude lateral head beat cross frequency, and hyperactivity using computer-assisted sperm analysis, viability, and spermatozoa abnormalities.

Results

The CEP-3(m) diluent formula and ASE 1 at a 30% level maintained the PM of spermatozoa up to day 5 (40.7% ± 16.1%) of cold storage. Meanwhile, the CEP-3(m) diluent formula and ASE 2 could only maintain PM >40% until day 3 (42.1% ± 13.5%) of cold storage at a 30% level. The CEP-3(m) diluent and ASE 1 at a level of 25%-30% supported spermatozoa life (viability) up to day 5 with a value >80% (81.8 ± 3.5; 86.4 ± 2.6). The abnormality value of spermatozoa in various diluents during cold storage on days 0-5 was below 20%.

Conclusion

Soybean extracts 1 and 2 can substitute EYs as extracellular cryoprotectants in modified CEP-3 basic diluents. Soybean extract 1 can support the life of spermatozoa up to day 5 but may cause the viscosity and movement of spermatozoa to be hyperactive. Soybean extract 2 can support the life of spermatozoa up to the 3rd day of cold storage and produces progressive (non-rotating) movement patterns. Further, research is recommended with higher levels of ASE 2.

Review: Development, adoption, and impact of assisted reproduction in domestic buffaloes

The domestic buffalo (Bubalus bubalis), also known as water buffalo, comprises two sub-species the River buffalo (B. bubalis ssp. bubalis; 50 chromosomes) and the Swamp buffalo (ssp. carabanensis; 48 chromosomes). Domestic buffaloes are a globally significant livestock species. In South Asia, the River buffalo is a primary source of milk and meat and has a very important role in food security. The River buffalo also supports high-value, differentiated food production in Europe and the Americas. The Swamp buffalo is an important draft animal and a source of food in Southeast Asia and East Asia. The growing importance of buffaloes requires that they undergo an accelerated rate of genetic gain for efficiency of production, product quality, and sustainability. This will involve the increased use of assisted reproduction. The initial application of reproductive technology in buffaloes had variable success as it relied on the adoption of procedures developed for cattle. This included artificial insemination (AI), sperm cryopreservation, and embryo technologies such as cloning and in vitro embryo production (IVEP). Reproductive technology has been progressively refined in buffaloes, and today, the success of AI and IVEP is comparable to cattle. Ovarian follicular superstimulation (superovulation) combined with in vivo embryo production results in low embryo recovery in buffaloes and has limited practical application. The contribution of elite female buffaloes to future genetic improvement will therefore rely mainly on oocyte pickup and IVEP. This will include IVEP from females before puberty to reduce generation intervals. This review provides for the first time a clear chronology on the development, adoption, and impact, of assisted reproduction in domestic buffaloes.

Fertility results after exocervical insemination using goat semen cryopreserved with extenders based on egg yolk, skim milk, or soybean lecithin

To evaluate the effects of four extenders on the post-thaw quality and fertility of goat semen, six Yunshang Black bucks' semen was collected, pooled, diluted with Andromed® (Andr®), Optidyl® (Opt®), P3644 Sigma l-phosphatidylcholine (l-α SL), and skim milk-based (Milk) extenders, and then cryopreserved. The sperm motilities, abnormalities, membrane and acrosome integrity, mitochondrial activity, apoptosis, and reactive oxygen species (ROS) production were evaluated after thawing. After exocervical insemination with the thawed semen, the pregnancy, lambing, and twinning rates were recorded and compared. The results showed that sperm motilities, membrane integrity, acrosome integrity, mitochondrial activity, and viable spermatozoa were significantly higher in the Andr® and Opt® groups than those in the l-α SL and Milk groups (p < .05). Furthermore, there was no difference between Andr® and Opt® (p > .05). The sperm abnormality was lower in semen frozen with the Andr® or Opt® extenders, as compared to the l-α SL or Milk extender (p < .05). Regarding, the viable cells with low ROS production, the optimal results were obtained in the semen frozen with Andr® and Opt® extenders. Following exocervical insemination, the pregnancy and lambing rates in the Milk group were significantly lower than those in the other groups (p < .05). No difference was found in the pregnancy and lambing rates between Andr®, Opt®, and l-α SL (p > .05). Furthermore, the twinning rates were similar between these four groups (p > .05). In conclusion, egg yolk or skim milk can be substituted by soybean lecithin during cryopreservation of goat semen.

Germplasm cryopreservation in bulls: Effects of gonadal tissue type, cryoprotectant agent, and freezing-thawing rates on sperm quality parameters

Germplasm preservation is crucial for reproductive programs involving farm and endangered species. This study describes the effects of slow-uncontrolled cryopreservation protocols on bovine sperm associated with testicular or epididymal tissues. Samples from the testis or epididymis (cauda) were cut into ∼0.5 or 1 cm³ fragments and cryopreserved using Me2SO (Dimethyl Sulfoxide) or glycerol-based cryoprotectants. Sperm were collected from testicular or epididymal tissue before and after freezing-thawing (38 °C or 40 °C) and kept at room temperature (RT) or 4 °C during handling. The parameters studied were viability, membrane integrity (HOS), motility, acrosome integrity, chromatin, and morphology. Pre-freezing parameters were lower in testicular sperm than epididymal: HOS+ and DNA integrity (P < 0.05). Normal-% pre-freezing testicular sperm morphology was lower than epididymal (43.3 ± 1.8% vs. 65.3 ± 14.8%). All testicular RT-kept sperm parameters decreased post-freezing, except for acrosome integrity, which remained constant (P > 0.05). There were no differences in Me2SO-frozen tissue sizes (P > 0.05). All epididymal RT-kept sperm parameters dropped post-freezing except for the constant DNA integrity (P > 0.05). 4^oC-kept sperm were fitter than those at RT (P < 0.05). 4^oC-kept testicular sperm viability, DNA, and membrane integrities declined after 38 °C or 40 °C thawing (P < 0.05). Acrosome integrity and motility remained unchanged after freezing (P > 0.05). 4^oC-kept epididymal sperm acrosome integrity, motility, and HOS+% severely dropped post-thawing (P < 0.05). Viability and DNA integrity were unchanged (38 °C vs. 40 °C; P > 0.05). Overall, post-freezing sperm morphology was unaffected (P > 0.05), but Dag defect was significantly lower in testicular samples (P < 0.05). Whole-epididymis parameters were maintained up to 24h at 4 °C (P > 0.05). In conclusion, testis-epididymis freezing protocols should use small tissue pieces, Me2SO-based cryoprotectants, and 4°C-kept samples to reduce sperm damage.

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.

Extend the Survival of Human Sperm In Vitro in Non-Freezing Conditions: Damage Mechanisms, Preservation Technologies, and Clinical Applications

Preservation of human spermatozoa in vitro at normothermia or hypothermia maintaining their functions and fertility for several days plays a significant role in reproductive biology and medicine. However, it is well known that human spermatozoa left in vitro deteriorate over time irreversibly as the consequence of various stresses such as the change of osmolarity, energy deficiency, and oxidative damage, leading to substantial limitations including the need for semen examinations, fertility preservation, and assisted reproductive technology. These problems may be addressed with the aid of non-freezing storage techniques. The main and most effective preservation strategies are the partial or total replacement of seminal plasma with culture medium, named as extenders, and temperature-induced metabolic restriction. Semen extenders consist of buffers, osmolytes, and antioxidants, etc. to protect spermatozoa against the above-mentioned adverse factors. Extended preservation of human spermatozoa in vitro has a negative effect on sperm parameters, whereas its effect on ART outcomes remains inconsistent. The storage duration, temperature, and pre-treatment of semen should be determined according to the aims of preservation. Advanced techniques such as nanotechnology and omics have been introduced and show great potential in the lifespan extension of human sperm. It is certain that more patients will benefit from it in the near future. This review provided an overview of the current knowledge and prospects of prolonged non-freezing storage of human sperm in vitro.

Boar Sperm Cryopreservation Improvement Using Semen Extender Modification by Dextran and Pentaisomaltose

The long-term storage of boar sperm presents an ongoing challenge, and the modification of the cryoprotective compounds in semen extenders is crucial for improving cryopreservation’s success rate. The aim of our study was to reduce the percentage of glycerol in the extender by elimination or substitution with biocompatible, non-toxic polysaccharides. For boar semen extender improvement, we tested a novel modification with the polysaccharides dextran and pentaisomaltose in combination with unique in silico predictive modeling. We targeted the analysis of in vitro qualitative sperm parameters such as motility, viability, mitochondrial activity, acrosome integrity, and DNA integrity. Non-penetrating polysaccharide-based cryoprotective agents interact with sperm surface proteins such as spermadhesins, which are recognized as fertility markers of boar sperm quality. The in silico docking study showed a moderate binding affinity of dextran and pentaisomaltose toward one specific spermadhesin known as AWN, which is located in the sperm plasma membrane. Pentaisomaltose formed a hydrophobic pocket for the AWN protein, and the higher energy of this protein–ligand complex compared with dextran was calculated. In addition, the root mean square deviation (RMSD) analysis for the molecular dynamics (MD) of both polysaccharides and AWN simulation suggests their interaction was highly stable. The in silico results were supported by in vitro experiments. In the experimental groups where glycerol was partially or entirely substituted, the use of pentaisomaltose resulted in improved sperm mitochondrial activity and DNA integrity after thawing when compared with dextran. In this paper, we demonstrate that pentaisomaltose, previously used for cryopreservation in hematopoietic stem cells, represents a promising compound for the elimination or reduction of glycerol in extenders for boar semen cryopreservation. This novel approach, using in silico computer prediction and in vitro testing, represents a promising technique to help identify new cryoprotectants for use in animal breeding or genetic resource programs.

Spermatozoa Survival in Egg Yolk-Based and Soybean-Based Extenders at Ambient and Chilling Temperature in Domestic Turkeys (Meleagris gallopavo)

Populations of many galliform species have declined mainly due to habitat loss and over-hunting, notably the Congo peacock, which has been classified as a vulnerable species by the International Union for Conservation of Nature (IUCN). The domestic turkey, being a species of least concern, which has been reported to be closely related to peacocks, could serve as a model for the optimization of assisted reproductive technologies for the Congo peacock. This study was aimed at developing a suitable turkey semen extender for artificial insemination in field conditions. Semen was collected using the dorso-abdominal massage technique from seven turkey toms and analyzed. Ejaculates with >70% motility and >80% live spermatozoa were pooled and divided into four aliquots (four treatments). Each of the four treatments was extended in a soybean-based extender or an egg yolk-based extender, with or without L-ascorbic acid. Two liquid preservation protocols (ambient temperature (35 °C) and chilled (4 °C)) were employed, and quality parameters including motility, viability and morphology were evaluated. The results show that the two extenders were similar with regard to semen quality parameters, and L-ascorbic acid supplementation of the turkey semen extenders improved semen quality during liquid storage.

The Natural Cryoprotectant Honey for Fertility Cryopreservation

Honey is a mixture of 25 sugars with other bioactive substances (i.e., organic acids, enzymes, antioxidants, and vitamins) and has been known as a highly nutritious functional food. Traditionally, it has been widely used in medicinal applications to cure various diseases. The effectiveness of honey in different applications has been used for its antimicrobial activity, absorption of hydrops, cleansing, removing odor, assisting granulation, recovery of nutrition, and formation of tissue and epithelium, which proved that honey has dehydrating and preserving properties to make it ideal for the cryopreservation of cells and tissues. Cryopreservation is an advanced preservation technique for tissue, cells, organelles, or other biological specimen storage, performed by cooling the sample at a very low temperature. It is the most common approach to improved preserving fertility (sperm, embryos, and oocytes) in different species that may undergo various life-threatening illnesses and allows for the genetic screening of these cells to test the sample for diseases before use. However, with toxic cryoprotectant (CPA), cryopreservation of fertility has been challenging because of their particular structure and sensitivity to chilling. Honey’s unique composition, as well as its dehydrating and preserving properties, qualify it to be used as a natural cryoprotectant. The aim of this study is to emphasize the ability of honey as a natural cryoprotectant in cryopreservation. The articles for this review were searched from Google Scholar, PubMed, Science Direct, Web of Science, and Scopus, using the keywords, honey, cryopreservation, natural cryoprotectant/CPAs, extenders, and fertility. Honey, as a natural cryoprotectant in fertility cryopreservation, yielded satisfactory results, with respect to improved post-thaw quality and viability. It is now proved as a non-toxic and highly efficient natural cryoprotectant in fertility preservation because its increasing viscosity at low temperature can provide a protective barrier to cells by reducing ice formation. Furthermore, its antioxidant property plays a vital role in protecting the cells from thermal damage by reducing the reactive oxygen species (ROS). This review provides a road map for future studies to investigate the potential of honey in the cryopreservation of other cells and tissue and contribute to the scientific research, regarding this remarkable natural product.

Chlorogenic Acid Improves Quality of Chilled Ram Sperm by Mitigating Oxidative Stress

Simple Summary

Sheep sperm is extremely sensitive to reactive oxygen species (ROS) and can produce a large amount of ROS during chilling storage, leading to a decline in semen quality. Adding antioxidants is an important method to improve semen quality. Chlorogenic acid (CGA) is a kind of plant extract with an antioxidant capacity, which can effectively eliminate free radicals and improve the antioxidant capacity of semen. However, its role in the chilling storage of Hu ram semen is not clear. Therefore, CGA with different concentrations was added to chilling storage extender to investigate its effect on chilled ram sperm. The results of this study revealed that CGA with proper concentration had a positive effect on chilled Hu ram sperm and 0.8 mg/mL CGA had the best effect.

Abstract

The purpose of this study was to investigate whether the addition of chlorogenic acid (CGA) to a sheep semen extender could improve the quality of chilled sheep sperm. Ejaculates (n = 80) were collected from five Hu rams with an artificial vagina. The ejaculates were mixed and divided into five equal parts, diluted with a CGA-free Tris–egg yolk extender (control), or supplemented with 0.2, 0.4, 0.8, and 1.2 mg/mL. The sperm kinematic parameters (viability, progressive motility), functional integrity of plasma membrane and acrosome, adenosine triphosphate (ATP) concentration and antioxidant parameters (Catalase (CAT), Superoxide dismutase (SOD) activity, total antioxidant capacity (T-AOC), ROS level and Malondialdehyde (MDA) content) were evaluated during storage of the semen. The results indicated that: PM, plasmatic membrane integrity and acrosomal integrity in 0.8 mg/mL CGA were higher (p < 0.05) from day 1 to 5. The ROS level in CGA groups was lower than the control (p < 0.05). CAT, SOD, ATP, and T-AOC were highest at 0.8 mg/mL concentration within 1 to 5 days. The above results indicated that the right concentration of CGA improved the quality of Hu ram sperm during chilling storage.

The effects of egg yolk-based and egg yolk-free diluents on the post-thaw quality of bull spermatozoa

The aim of this study was to evaluate the effects of 3 different commercially available extenders – AndroMed® (soy lecithin-based), Optidyl® (with the addition of ionized egg yolk), and BULLXcell® (with the addition of fresh egg yolk) – on bull spermatozoa quality, which was evaluated using the parameters of spermatozoa motility, viability, plasma membrane damage, acrosome damage, and mitochondrial activity after thawing and during a 2 h long thermoresistance test. The spermatozoa quality indicators were appraised by computer-assisted semen analysis and a flow cytometer. Significant differences (P < 0.01) between bulls were registered in all indicators measured. The highest average values of spermatozoa total motility and viability were achieved using BULLXcell® extender (44.33%; 52.06%). Variances in comparing this extender with Optidyl® and AndroMed® were −0.83%, −2.64%; −8.33%, −9.51%. The differences found between the egg yolk-based diluents (BULLXcell® and Optidyl®) and AndroMed® were significant (P < 0.01). Therefore, the more valuable extenders for bull semen dilution were egg yolk-based extenders, which provided higher post-thaw spermatozoa survival and quality than the soy lecithin-based extender.

Assessment of coconut water added to Numida meleagris egg yolk as cryoprotectant for goat semen

Effects were assessed of the dilutants TRIS and ACP - 101c® with the addition of different guinea fowl (Numida meleagris) egg yolk concentrations. Fifteen ejaculates were collected from five goats of the Anglo Nubian breed. The ejaculates were pooled and then divided into 12 groups, two control groups (GC1 TRIS, with 2.5% Gallus gallus domesticus hen egg yolk GOGD), (GC2 Control Group ACP - 101c®, with the addition of 2.5% Gallus gallus domesticus hen egg yolk GOGD) and ten experimental groups (EG), containing TRIS and ACP added with different concentrations of egg yolk from guinea hen (Numida meleagris) (TRIS 2,5% GONM; TRIS 5% GONM; TRIS 10% GONM; TRIS 15% GONM; TRIS 20% GONM; ACP® 2,5% GONM; ACP® 5% GONM; ACP® 10% GONM; ACP® 15% GONM; ACP® 20% GONM). Then cryopreservation was carried out and the samples stored in liquid nitrogen (-196 °C). After seven days, the samples were thawed and assessed for spermatic kinetics, immunofluorescence and sperm morphology. Analysis of GOMN by the CASA system showed that the various parameters were similar to those of GOGD (P>0.05). The membrane integrity, mitochondrial potential and the acrosome were not influenced by the treatment (P>0.05) nor by the dilutant used for cryopreservation (P>0.05). The spermatic morphology was also preserved by the different GOGD and GONM concentrations in the ACP® and TRIS dilutants, with no statistically significant differences (P<0.05). It was concluded that Numida meleagris egg yolk, as external membrane cryoproctant added to the dilutants ACP-101c® and TRIS, improved goat semen quality.

The Use of κ-Carrageenan in Egg Yolk Free Extender Improves the Efficiency of Canine Semen Cryopreservation

κ-Carrageenan is a plant polysaccharide derived from red seaweeds reported to possess potential medicinal and antioxidants activities. The present study aimed to identify the cryoprotective effects of κ-carrageenan on the quality of frozen-thawed canine semen. Twenty-eight ejaculates were collected and diluted in a Tris egg-yolk-free extender supplemented with various concentrations of κ-carrageenan (0.0%, 0.1%, 0.2%, 0.3%, and 0.5%). The addition of κ-carrageenan to the extender at a 0.2% concentration induced a significant increase in the total motility (TM) and the rapid progressive motility (RPM) of canine sperm. Among the experimental groups, the highest percentage of sperms with intact acrosomes was found in the 0.5% κ-carrageenan group (p < 0.05). Apoptosis levels were significantly lower in the 0.1% and 0.2% κ-carrageenan treatment. Moreover, sperm in the κ-carrageenan supplemented group showed a significantly higher expression of antiapoptotic (Bcl-2) and lower expression of NADPH oxidase (NOX5), spermine synthase (SMS), and spermine oxidase (SMOX) genes than those in the control group. In conclusion, the addition of κ-carrageenan to the freezing extender improved the overall efficiency of frozen-thawed dog spermatozoa.

The Role of the Natural Antioxidant Mechanism in Sperm Cells

Molecular studies of the causes of male infertility revealed a significant contribution of oxidative stress. When excessive amounts of reactive oxygen species (ROS) are produced or antioxidant activity fails, the equilibrium between oxidation and reduction is disrupted, causing oxidative stress (OS). High levels of ROS can have an adverse effect on sperm function through the initiation of DNA damage, lipid peroxidation, loss of membrane integrity and increased permeability, inactivation of cellular enzymes, and cell apoptosis. In addition to endogenous factors such as immature sperm, leukocytes, and varicocele, potential causes of excessive ROS can also be found exogenously in males with testicular hyperthermia or exposed to environmental toxicity. To maintain the optimal functioning of sperm cells, it is, therefore, necessary to balance the redox potential, i.e., to balance ROS by antioxidants. The purpose of this review is to present the antioxidant defense systems in semen.

The addition of crocin in the freezing medium extender improves post-thaw semen quality

Semen cryopreservation is arguably the most important method or technique contributing to the advancement of modern animal production. However, the quality of sperm after thawing is still highly variable. The addition of antioxidant compounds to the freezing medium has been used customarily to counteract the harmful effects of Reactive Oxygen Species (ROS) that are produced during the freeze/thaw process. Crocin, a potent antioxidant, improves the fertilizing capacity of spermatozoa. In this study, we evaluated the potential of crocin (0, 0.5 and 1 mM) as an extender additive to diminish the damaging effects of cryopreservation on bovine spermatozoa. Post-thaw semen quality was assessed by means of motility, viability and lipid peroxidation (LPO). We further investigated the effect of crocin supplementation upon freezing on sperm quality parameters during their incubation at 37°C for up to 2 hr. Overall, the data assessment indicates that crocin facilitated a general improvement of the quality of freeze/thawed spermatozoa, under the present experimental conditions. Crocin (1 mM) maintained a higher percentage of alive spermatozoa with intact acrosome with rapid and progressive motility, compared to the control extender. Moreover, the spermatozoa cryopreserved in the presence of crocin exhibited higher values in CASA kinematic parameters (VCL, VSL, VAP, ALH) immediately after thawing. Furthermore, the positive effect of crocin on motility parameters was also sustained over a period of 2 hr incubation at 37°C. This effect of crocin may be attributed to the observed inhibition of LPO during the incubation period. Thus, the results indicate that the addition of crocin (especially at a final concentration of 1 mM) in the freezing extender medium may benefit the preservation of the quality parameters of spermatozoa that are compromised by the freeze/thaw heat shock and the stress during handling for IVF or artificial insemination.

Epigallocatechin 3-gallate improves the quality of bull semen cryopreservation

To determine the effects of epigallocatechin-3-gallate (EGCG) on the cryopreservation of bovine semen, epigallocatechin-3-gallate dissolved with double distilled water to 0.2, 0.4, 0.6 and 0.8 mg/ml were added to the cryopreservation diluent of the bull semen. Then, we used computer-assisted analysis of semen kinematic parameters, staining method to detect membrane function, acrosome integrity, enzyme-linked immunosorbent assay to detect catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malondialdehydes (MDA) and reactive oxygen levels. The results showed that adding 0.6 mg/L of epigallocatechin-3-gallate could improve the cryopreserved sperm quality, which significantly increased the total motility, distance average path, distance straight line, distance curved line, average path velocity, curvilinear-velocity, straight-line velocity, amplitude of lateral head displacement and beat/cross frequency, as well as sperm CAT, GSH-Px and SOD levels (p < 0.05), whilst reducing the reactive oxygen species and MDA levels (p < 0.05). Hence, these results indicate that the addition of 0.6 mg/ml of EGCG has a protective effect on the cryopreservation of the bovine semen.

Application of High Hydrostatic Pressure (HHP) to Improve Cryopreservation of Young Bull Semen

The objective of the study was to determine the effect of high hydrostatic pressure (HHP) on quality of cryopreserved semen of young bulls. Semen for this study was collected from 8 bulls aged between 13 and 18 months at monthly intervals, from June to September. After collection, semen was diluted in a commercial Bioxcell® extender (one part at 1:1 and a second part to give a sperm concentration of 20 million/0.2 mL), filled into straws and treated with HHP at 30 MPa for 90 min. After HHP treatment, pre-diluted semen (1:1) was diluted to a sperm concentration 20 million/0.2 mL and filled into straws. In addition, part of the semen diluted to a concentration of 20 million/0.2 mL was not treated with HHP (control). All of it was held at +4°C and frozen in a freezer after 2.5-h equilibration. Semen was thawed in a water bath at 38°C and subjected to estimation of the percentage of motile sperm both subjectively and using a computer-assisted semen analyzer and cytometric assessment of sperm cell membrane integrity. Subjective motility and fast progressive motility were significantly higher with pre-diluted (1:1) and HHP treated semen compared to control (P<0.05). No significant differences were observed in percentage of membraneintact spermatozoa between control and experimental groups. Additionally, the influence of HHP on the sperm of individual bulls was assessed. In bull number 2, the HHP treatment after semen pre-dilution significantly improved progressive motility from 54.1 to 63.4 percent (P<0.05). In bull number 4, the HHP treatment after semen pre-dilution significantly improved subjective motility, rapid motility and progressive motility by 12.5, 16.8 and 16.3 percent, respectively (P<0.05). No effect was seen for 6 bulls. It is concluded that for some bulls, the application of HHP before semen freezing may improve the cryopreservation outcome. However, this requires further research in this area, also to determine the fertilizing capacity of bull semen exposed to high hydrostatic pressure.

Association between Fatty Acid Composition, Cryotolerance and Fertility Competence of Progressively Motile Bovine Spermatozoa

An association between progressive motility (PM) and spermatozoa fertility competence has been suggested. However, the mechanism that underlies PM is not clear enough. We examined physiological characteristics and fatty acid composition of fresh spermatozoa with high and low PM. Additional analysis of fatty acid composition and structural characteristics was performed on spermatozoa samples with high and low progressively motile spermatozoa's survival (PMSS), i.e., the ratio between the proportion of progressively motile spermatozoa after and before cryopreservation. Finally, a fertility field trial was conducted to examine the association between the number of PM spermatozoa within the insemination straw post thawing and conception rate. Analysis of fresh spermatozoa revealed a higher omega-6 to omega-3 ratio in ejaculates with low PM relative to those with high PM (p < 0.01). The proportion of polyunsaturated fatty acids was higher in low-PMSS fresh samples (p < 0.05) relative to their high-PMSS counterparts. Fresh samples with high-PMSS expressed a higher mitochondrial membrane potential (p < 0.05) and a higher proportion of viable cells that expressed reactive oxygen species (ROS; p < 0.05). Post-thawing evaluation revealed a reduced proportion of progressively motile sperm, with a prominent effect in samples with high PM relative to low PM, defined before freezing (p < 0.01). No differences in spermatozoa mitochondrial membrane potential or ROS level were found post-thawing. A fertility study revealed a positive correlation between the number of progressively motile spermatozoa within a standard insemination straw and conception rate (p < 0.05). Considering these, the bull PMSS is suggested to be taken into account at the time of straw preparation.

Cholesterol-loaded cyclodextrin attenuates dilution effect and improves quality of bovine low sperm insemination doses during cryopreservation

In the present study, the effect of cholesterol-loaded cyclodextrin (CLC) on the quality of low sperm doses at post-thaw was evaluated. Twenty four ejaculates (6 from each bull) were collected and split into eight aliquots. First four aliquots were diluted up to 20-, 15-, 10- and 5-million sperm/0.25 ml, and remaining four were treated with CLC at the rate of 1 mg/120 million spermatozoa, followed by dilution up to 20-, 15-, 10- and 5-million sperm/0.25 ml. The diluted semen was equilibrated, cryopreserved and evaluated post-thaw. The averages of total motility, progressive motility, average path velocity, straight linear velocity, membrane intact spermatozoa and noncapacitated spermatozoa were higher (p < .05) in CLC-treated sperm doses compared to control ones. However, the moribund spermatozoa, capacitated spermatozoa and acrosome-reacted spermatozoa were reduced (p < .05) in CLC-treated spermatozoa compared to control. The curvilinear velocity and linearity did not differ (p > .05) between control and CLC-treated sperm doses. In conclusion, treatment of spermatozoa with CLC at the rate of 1 mg/120 million spermatozoon attenuates the dilution effect and improves the quality of bovine low sperm insemination doses during cryopreservation; hence it could be a favourable cryoprotectant for preserving bovine semen at higher dilutions.

Dynamics of mitochondrial membrane potential and DNA damage during cryopreservation of cattle and buffalo bull spermatozoa

Understanding the changes in the spermatozoa during cryopreservation is indispensable for tailoring and increasing the efficiency of cryopreservation process success. However, the dynamics of damage to sperm organelles during different stages of cryopreservation is underexplored. This study assessed the mitochondrial membrane potential (MMP) and DNA damage during different stages of cryopreservation, viz. immediately after ejaculation, after equilibration and after freezing and thawing in cattle and buffalo spermatozoa using flow cytometry. Proportion of spermatozoa with high MMP decreased significantly after equilibration (from 66.06±4.59 to 42.58±6.30 in Holstein bulls and from 60.32±5.51 to 39.98±7.58 in buffalo bulls). Sperm DNA integrity [DNA fragmentation index (DFI %)] in Holstein Friesian (HF) bulls did not differ significantly between fresh and equilibrated samples but a significantly higher % DFI was observed in frozen-thawed semen samples as compared to both fresh and equilibrated samples. In contrast, % DFI in buffalo spermatozoa did not differ among the three stages of cryopreservation. It was concluded that mitochondrial damages occur during equilibration while chromatin damages occur during freezing and thawing of cattle bull spermatozoa; whereas buffalo bull spermatozoa were lesser susceptible to DNA damage during cryopreservation as compared to cattle spermatozoa.

Effects of Extender Type, Storage Time, and Temperature on Bull Semen Parameters

Seminal parameters can be evaluated in situ, or samples can be delivered to a diagnostic centre. How storage conditions affect ejaculates up to evaluation is unclear. We assessed, in 25 commercial bulls electroejaculated in the field, the impact of time until evaluation (0-2 h, 4-6 h, and 24 h post-ejaculation), holding temperature (5 °C vs. room temperature), and extender (AndroMed^®, BIOXcell^® or INRA96^®) on semen quality. Acrosome integrity, sperm viability and morphology, CASA-total and progressive motility, pH, and colony-forming units were assessed. Semen quality was preserved for up to 4-6 h post-ejaculation, except for INRA96^® at 5 °C. Regardless of extender or temperature, motility decreased from 4 to 6 h up to 24 h, with the best values obtained with BIOXcell^® at 5 °C. pH differed from 4 to 6 h up to 24 h, acidifying when stored at room temperature. Microbiological load was stable over time with AndroMed^® and BIOXcell^®, and increased at room temperature with INRA96^®. Our results suggest that AndroMed^® and BIOXcell^® can preserve semen quality for up to 6 h, either at 5 °C or room temperature, while INRA96^® only at room temperature. These results help to fix adequate protocols for short-term storage and shipment of bovine semen collected under field conditions.

Effects of Apigenin and Astragalus Polysaccharide on the Cryopreservation of Bull Semen

The purpose of this study was to determine the effects of apigenin and astragalus polysaccharides on the cryopreservation of bovine semen. Apigenin, astragalus polysaccharides, or their combination were added to a frozen diluent of bovine semen. Afterwards, Computer Assisted Semen Analysis (CASA), membrane functionality, acrosome integrity, mitochondrial integrity, CAT, SOD, GSH-Px, MDA, and ROS detection were conducted. The results showed that adding 0.2 mmol/L AP or 0.5 mg/mL APS could improve the quality of frozen sperm. Compared to 0.2 mmol/L AP alone, the combination of 0.2 mmol/L AP and 0.3 mg/mL APS significantly increased the total motility (TM), average path distance (DAP), straight line distance (DSL), average path velocity (VAP), curvilinear velocity (VCL), wobble (WOB), and sperm CAT and SOD levels (p < 0.05), while reducing the ROS and MDA levels (p < 0.05). These results indicated that the addition of 0.2 mmol/L AP or 0.5 mg/mL APS alone has a protective effect on the freezing of bovine semen. Compared to the addition of 0.2 mmol/L AP, a combination of 0.2 mmol/L AP and 0.3 mg/mL APS could further improve the quality of frozen semen.

Semen extenders: An evaluative overview of preservative mechanisms of semen and semen extenders

Reproduction is fundamental for all living things as it ensures the continued existence of a species and an improved economy in animal husbandry. Reproduction has developed since history, and diverse processes, such as artificial insemination and in vitro fertilization, have been developed. Semen extenders were discovered and developed to protect sperm from harmful factors, such as freeze and osmotic shock, oxidative stress, and cell injury by ice crystals. Semen extenders preserve sperm by stabilizing its properties, including sperm morphology, motility, and viability and membrane, acrosomal, and DNA integrity. Therefore, semen extenders must provide a favorable pH, adenosine triphosphate, anti-cooling and anti-freeze shock, and antioxidant activity to improve semen quality for fertilization. Hence, this review provides precise data on different semen extenders, preservative mechanisms, and essential additives for semen extenders in different animals.

Cryopreservation of dog semen in a Tris extender with two different 1% soybean preparations compared with a Tris egg yolk extender

Egg yolk is widely used as a cryoprotectant in dog semen extenders, but there is a risk of contamination with animal pathogens. In addition, egg yolk may vary in composition, making it difficult to standardize the extender. Lecithin is an animal protein-free alternative to egg yolk for semen cryopreservation. Recently, it was shown that 1% of soybean lecithin type II-S was better than 2% for freezing canine semen. The aim of the study was to compare two different types of soybean lecithin, with egg yolk as a control. Ejaculates from eight dogs were divided into three equal parts and diluted with a Tris-based extender, containing either 20% egg yolk, 1% soybean lecithin Type II-S or 1% soybean lecithin Type IV-S. The samples were then frozen. Sperm motility was evaluated by computer-assisted sperm analysis (CASA), acrosome integrity (FITC-PNA/PI) and sperm membrane integrity (SYBR-14/PI) post-thaw, as well as after 2 and 4 hr incubation at 37°C. Post-thaw sperm chromatin structure assay and plasma membrane integrity were evaluated by flow cytometry. Total motility, sperm plasma membrane integrity and acrosome integrity were significantly better in the egg yolk extender than in the two soybean lecithin-based extenders. Individual motility post-thaw differed more than in the fresh samples, illustrating individual differences in tolerance to the cryostress. The DNA Fragmentation Index (% DFI) was significantly lower in the Tris egg yolk (TEY) extender compared to any of the soybean-based extenders. The number of high green stained spermatozoa were significantly higher in Type IV-S compared to the control TEY extender. In conclusion, egg yolk was superior to the two lecithin-based extenders to cryopreserve canine semen.

Cholesterol-cyclodextrin complex as a replacement for egg yolk in bull semen extender: sperm characteristics post-thawing and in vivo fertility

Egg yolk, a major semen extender constituent, lacks a defined composition, therefore, there are biosecurity concerns with use of egg yolk. Cryopreservation of bull semen without inclusion of animal protein in the semen extender, therefore, is an important consideration. Cholesterol may be delivered and incorporated into the sperm plasma membrane by cyclodextrins to protect sperm during cryopreservation. The aim of this study was to determine suitability of a cholesterol-cyclodextrin semen extender, without inclusion of egg yolk, for cryopreservation of bull semen. Bull semen was collected and cryopreserved in either egg yolk or with inclusions of three different concentrations of cholesterol-cyclodextrin complex (0.5, 1 or 2 mg/mL semen) in Tris-glycerol (TG) extender. Sperm motion characteristics examined using the computer-assisted sperm analysis, and plasma membrane and acrosome integrity examined using flow cytometry, were similar for all extenders. The inclusion of the greatest concentration of cholesterol-cyclodextrin complex (2 mg/mL semen) followed by dilution in TG extender resulted in lesser pregnancy rates (P <  0.05). There was a pregnancy rate of as great as 56 % when sperm cryopreserved in 0.5 mg/mL cholesterol-cyclodextrin Tris-glycerol extender were used for artificial insemination following imposing of a hormonal treatment regimen for synchrony of timing of ovarian functions among cows for conducting fixed-time artificial insemination (FTAI). Results indicate cholesterol-cyclodextrin Tris-glycerol extender, with a chemically defined composition and without inclusion of egg yolk, may be used to cryopreserve bull sperm with there being acceptable pregnancy rates when this semen is used for FTAI.

Semen extender and seminal plasma alter the extent of neutrophil extracellular traps (NET) formation in cattle

During artificial insemination in bovine, the deposition of semen into the uterus results in an immune reaction which is based on polymorphonuclear neutrophils activity, including the formation of neutrophil extracellular traps. The formation of neutrophil extracellular traps as a reaction of neutrophils to spermatozoa was recently described. However, it is not completely clear which components of the semen are responsible for this reaction. The objective of this study was to quantify and compare the formation of neutrophil extracellular traps following in vitro incubation of bovine polymorphonuclear neutrophils with semen and extenders of different origins and conditions. We investigated the interactions between bovine polymorphonuclear neutrophils and different semen extenders, various seminal plasma concentrations from young and old bulls as well as sexed and non-sexed semen and their corresponding extenders. Three different semen extenders from two companies in fresh and frozen-thawed conditions were compared. Fresh semen extenders showed higher neutrophil extracellular traps induction than did frozen-thawed ones. The formation of neutrophil extracellular traps were also dependent on the presence of seminal plasma. We could show that seminal plasma alone, without any sperm cells, induced the reaction and that the addition of at least 1% seminal plasma already resulted in the formation of neutrophil extracellular traps. Furthermore, seminal plasma from young bulls led to significant higher neutrophil extracellular traps induction. No difference between non-sex-sorted and sex-sorted sperm and its extenders was observed. Taken together, different semen extenders as well as the amount and origin of seminal plasma influence neutrophil extracellular traps formation, whereas sex-sorted sperm did not affect the reaction.

Cross-species efficacy of a chemically-defined, soy lecithin-based cryomedium for semen banking in imperiled wild felids

Felid semen has historically been frozen using an egg yolk-based cryopreservation medium. However, the use of egg introduces several potential concerns, such as variability in composition, microbial contamination, and regulatory issues. In the present study, our aim was to compare a chemically-defined, soy-based medium (SOY) to a commercial egg yolk-based medium (TEY) for the cryopreservation of sperm in four imperiled small cat species. Semen was collected from adult male cats (n = 6 black-footed cats; n = 6 sand cats; n = 4 fishing cats; and n = 7 Pallas' cats) via electroejaculation, split into two aliquots, and cryopreserved in SOY or TEY. Frozen-thawed samples were evaluated for sperm motility and rate of progressive motility (up to 24 h post-thaw) and acrosome status (0 and 6 h). No difference in post-thaw traits were observed between treatments in all four species. Heterologous IVF using oocytes collected laparoscopically from domestic cats demonstrated no difference among freezing treatments in percentage of mature oocytes that cleaved or the mean number of blastomeres at 48 h post-insemination. More spermatozoa frozen with SOY were bound to the zona pellucida in the sand cat (P = 0.018), but no treatment effect was observed in the other three species. These findings collectively demonstrate that SOY may be a preferable alternative to TEY for sperm cryopreservation in these four wild felid species.

The role of environmental optimization for storing bulls' sperm cells

Artificial insemination has achieved a dynamic increase in genetic progress, and this is due to the improvement of sperm preservation technology. In recent years, a lot of attention has been paid to optimizing bull sperm storage environment and objectifying methods of sperm quality analysis. This review presents bull sperm preservation methods and ways to modify their storage environment. The main purpose of sperm preparation for artificial insemination is to obtain sperm with a high percentage of viable, motile sperm with normal morphology and low DNA fragmentation rates. Currently conducted experiments indicate the possibility of improving the quality of insemination doses produced using various components enriching common diluents. However, despite extensive research, no better results have been achieved than obtaining insemination doses with sperm viability that exceeds just over 60%. Obtaining a very good quality of frozen semen seems to be still unachievable today.

Effect of low-density lipoproteins and trehalose on the quality of cryopreserved bovine semen

Background: In artificial insemination, chicken egg yolk is added to bovine semen to protect it during the cryopreservation process, although it contains substances that can affect the microbiological quality and metabolism of sperm. Objective: To evaluate post-thaw quality of bovine cryopreserved semen added with centrifuged and non-centrifuged egg yolk, low-density lipoproteins (LDL), and trehalose (T). Methods: Ten ejaculates from five bulls were cryopreserved under the treatments T1: pure egg yolk (PEY) at 20% v/v, T2: centrifuged egg yolk (CEY) at 20% v/v, T3: LDL at 8% v/v, T4: T at 100 mM, and T5: T at 100 mM plus LDL at 8% v/v (TLDL). Spermatic motility and kinetics, functional membrane integrity (FMI), structural membrane integrity (SMI), sperm vitality (SV) and abnormal morphology (AM) were assessed using the Sperm Class Analyzer (SCA®) system, hypoosmotic test (HOST), SYBR/PI probes, and eosin–nigrosin staining, respectively. A completely randomized design was used. Normal distribution of the variables was validated through the Kolmogórov– Smirnov test. A generalized linear model was used to determine sources of variation. Means were compared using the Tukey test. Results: Inclusion of CEY or LDL had a similar effect on sperm protection, and were superior for motility, kinetics and membrane integrity compared to the other treatments (p<0.05). CEY was superior for progressive motility (p<0.05). The cryoprotective action of LDL was similar to TLDL for motility and kinetics, SMI, SV, and AM (p<0.05). Inclusion of PEY and T resulted in the lowest semen quality (p<0.05). The use of T resulted in a reduction in FMI and SMI (p<0.05). No differences in AM between treatments were found (p>0.05). Conclusions: Egg yolk can be replaced by centrifuged egg yolk or low-density lipoproteins in the freezing extender used for bovine semen used in artificial insemination.

Improving the Rabbit Semen Cryopreservation Protocol: Comparison Between Two Extenders and Inseminating Doses

This study has been designed to optimize the semen freezing protocol in rabbits, in this regard we compared a Tris-citrate-glucose (TCG) extender with a commercial one (Cortalap®), that to the best of our knowledge has never been used up to now on the in vitro freezability and fertilizing ability of cryopreserved rabbit semen. Two different inseminating semen doses were considered. Five pooled semen samples were divided into two subsamples and each of them were diluted to a ratio 1:1 (v:v) with a freezing extender composed of TCG or Cortalap® containing 16% of dimethylsulfoxide and 0.1 mol/L of sucrose. The extended semen was filled into 0.25 mL plastic straws and frozen above a liquid nitrogen surface. After thawing (50°C/10 seconds) we determined sperm motility, viability, membrane functionality, acrosome and DNA integrity. Our results showed that the Cortalap® extender significantly improved the in vitro post-thaw sperm quality, in comparison to TCG. When we compared the extenders in vivo, no significant differences in the reproductive performances were observed independently by inseminating doses used. In this study we demonstrated that Cortalap® extender can be used as an alternative to TCG. Thus, the Cortalap® being a ready to use extender, implies a reduction of time, mistakes and microbial contaminations during its preparation. This discovery results as significant because it provides beyond an important contribution to the creation of the first Italian semen cryobank of rabbit breeds and also for livestock rabbit farms based on artificial insemination (AI) program.

Soy lecithin as a potential alternative to powdered egg yolk for buck sperm cryopreservation does not protect them from mitochondrial damage

The aim of this study was to address whether soy lecithin (SL) was an effective non-penetrating cryoprotectant for buck sperm cryopreservation in the presence of seminal plasma. There was also an attempt to determine the optimal concentration of BHT as an antioxidant in powdered egg yolk (PEY) or in SL based media. Two ejaculates were collected from six bucks and mixed ejaculates were aliquoted into washed, using centrifugation procedures, and unwashed samples. In Experiment 1, washed sperm were re-suspended in PEY (15%) or SL (1%) media, while unwashed semen was only diluted in SL medium. In Experiment 2, washed and unwashed sperm were diluted in PEY and SL media, respectively, with there being different BHT concentrations (0.6, 2.0 and 5.0 mM). In both experiments, after 4 h of refrigeration, there were no differences neither in sperm viability nor plasma membrane functional integrity (HOST) between groups when there were evaluations using eosin-nigrosine staining. After thawing, however, there was a negative effect on motility of washed sperm preserved in SL media. Furthermore, results from cytometry evaluations indicated there was a larger population of thawed sperm with intact plasma (SYBR-14+/PI-) and acrosome (PE-PNA-) membranes, but inactive mitochondria (Mitotracker deep red-) when SL media were used. When there was BHT supplementation, there was only a slight enhancement of motility of spermatozoa preserved in PEY media with 5 mM BHT. In conclusion, when effectiveness and efficiencies are considered, PEY is the non-penetrating cryoprotectant that should be utilized for buck sperm cryopreservation.

Effects of Leucosporidium-derived ice-binding protein (LeIBP) on bull semen cryopreservation

We examined the effect of ice‐binding protein derived from Leucosporidium (LeIBP) on the cryopreservation of bull semen and compared it with that derived from previously reported Antifreeze Protein III (AFPIII). Six concentrations of LeIBP (10^–1 ~ 10⁴ μg/ml) and AFPIII (10^–1 ~ 10⁴ μg/ml) were added to the bull semen extender, respectively. Sperm kinematic parameters were measured to examine sperm toxicity and cryopreserved sperm quality. Measures of antioxidant activity such as superoxide dismutase (SOD), reduced glutathione/oxidative glutathione (GSH/GSSG), and total antioxidant capacity (TAC) were analysed to identify the effect of LeIBP on sperm quality. In addition, sperm viability was analysed using a flow cytometer and fluorescence microscope by SYBR14/PI staining. The results showed that the LeIBP groups (0.1, 1 and 10 μg/ml) were less toxic, and the quality of the sperm were dramatically improved in the extenders containing 0.1 μg/ml LeIBP among concentrations of LeIBP and AFPIII. The SOD activity of LeIBP was greater than that of AFPIII and control. In addition, sperm viability was enhanced in the LeIBP‐treated group. In summary, LeIBP is a useful cryoprotective adjuvant for bull sperm cryopreservation, and the most efficient concentration of LeIBP is 0.1 μg/ml.

Cryopreservation of bison semen without exogenous protein in extender and its fertility potential in vitro and in vivo following fixed-time artificial insemination

Successful cryopreservation of bison semen is fundamental for restoration of genetic diversity in Canada's wood bison. Conventional bovine semen extenders contain animal products, such as egg yolk and milk, which are undesirable because of biosecurity risks and undefined composition. In this study, we examined the efficacy of an exogenous protein-free extender containing cholesterol-cyclodextrin complex (CC) to cryopreserve bison semen. The study also provided an opportunity to determine the effectiveness of different ovulation synchronization protocols for fixed-time artificial insemination in bison. Semen was collected from wood bison bulls via electroejaculation and cryopreserved in either Tris-egg yolk-glycerol (called 'TEYG') extender or pretreated with CC (2 mg/mL semen) and diluted in Tris-glycerol (collectively called 'CC-TG') extender. Post-thaw sperm motion characteristics and in vitro fertilization of cattle oocytes confirmed that CC alone without egg yolk protected bison sperm during cryopreservation process. In the first fertility trial, however, no pregnancy was obtained following fixed-time artificial insemination of bison cows with CC-TG extender. In a follow-up trial, low concentration of CC (1 mg/mL semen) resulted in better post-thaw sperm motion characteristics, fertility rate, and birth of live calves following fixed-time artificial insemination. Results showed that 1 mg CC/mL semen completely replaced egg yolk in bison semen extender. In addition, both follicular ablation and steroid treatment protocols provided ovulation synchrony to permit successful application of fixed-time artificial insemination in bison. This is the first report on the birth of live bison calves following fixed-time artificial insemination using semen cryopreserved in a defined extender.