Comparison of the Effects of Five Semen Extenders on the Quality of Frozen-Thawed Equine Epididymal Sperm

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.

Effect of sperm and glycerol concentration on epididymal sperm motility parameters after thawing

The aim of this study was to evaluate the effect of different glycerol concentrations and different sperm concentrations on stallion epididymal sperm motility indicators after thawing. For statistical analysis, 25 stallions were used. Collection of the epidydimal spermatozoa was performed as a retrograde flush of cauda epididymis and ductus deferens within 12 h post castration. After evaluation, the resuspended spermatozoa were centrifuged, the supernatant removed and the spermatozoa resuspended in Gent semen extender to get three different groups with different concentrations of sperm (250 × 106 in ml, 500 × 106 in ml, 1000 × 106 in ml) and different final glycerol concentrations (2%, 4%, and 6%). Therefore, 9 different samples were finally obtained from each stallion. The spermatozoa were packed and placed in a fridge (4 °C) for 2 h, then placed in liquid nitrogen vapour (−80 to −100 °C) and after 25 min plunged into the liquid nitrogen and stored at −196 °C for at least 5 days. The selected straws were individually thawed in a 38 °C water bath for 30 s prior to post-freezing analysis. Motility indicators were assessed at 0, 60, 120, and 180 min after thawing. Parametric test was used for analysis; the measured indicators were total motility, progressive motility, curvilinear velocity, straightness, and average-path velocity. In this study, the best results were reached in samples diluted into a concentration of 1,000 × 106 in ml, regardless of the concentrations of glycerol.

Slow cooling is beneficial for storage of frozen-thawed equine spermatozoa

Cooled storage of semen after thawing can expand the use of frozen semen, providing the possibility of thawing and evaluating the semen at the storage site and subsequently shipping the semen. Our objectives were (1) to examine the motility and viability of frozen-thawed semen after cooled storage and (2) to compare two cooled-storage protocols for frozen-thawed semen. The samples (n=31) were either placed immediately in a passive cooling box for 8 or 24h (CB) or placed in a refrigerator at 4°C for 30 minutes and then transferred to a passive cooling box (REF). Total and progressive motility were similar at T0 and T8-REF and at T0.5 and T8.5-REF. However, a significant reduction was observed in total motility (-8.12%) between T0 and T8-CB, and in total (-9.96%) and progressive motility (-8.52%) between T0.5 and T8.5-CB (p<0.05). A significant reduction was also observed in total and progressive motility between T0 and T24, and between T0.5 and T24.5 for both storage protocols (CB and REF). Viability was lower in T8.5-CB (-11.87%), in T8.5-REF (-9.65%), in T24.5-CB (-13.52%), and in T24.5-REF (-12.32%) compared to T0.5 (p<0.05). Our results demonstrate that sperm motility and viability decrease during cooled storage. However, storing the samples at 4°C for 30 minutes before placing the semen in a passive cooling box could mitigate the adverse effect of cooling during short-term storage (8hr). Additionally, we observed individual variation between samples indicating that this protocol might not be suitable for all stallions. Our data shows that slow cooling and storage of frozen-thawed semen is a valid alternative that allows the expansion of frozen semen in breeding programs.

Efficiency of Ringer B. Braun solution on stallion epididymal sperm motility and viability compared to the commercial extender within 72 hours of storage

Collection of epididymal stallion sperm offers the opportunity to retain and use genetic material from the males after elective castration or even post mortem. The aim of the present study was to evaluate the effect of the Ringer B. Braun solution on stallion epididymal sperm viability and motility during liquid storage for 72 h at 4 °C and at 20 °C. Eight stallions (3–10 years old) were used in the study. Sperm from the cauda epididymis was harvested immediately after routine castration. The sperm from epididymis was washed out and diluted with Ringer B. Braun solution and with a commercial semen extender which was used as a control. Samples from each horse were divided into two parts: one part of samples was stored at 4 ± 1 °C as recommended for the commercial semen extender, the other one was stored at 20 ± 1 °C. Sperm viability, motility, and pH were checked one hour after collection and dilution, and after 24, 48 and 72 h of incubation. The results of sperm viability, subjective and progressive sperm motility showed slightly higher results in semen samples diluted with Ringer B. Braun solution in one hour compared to the commercial extender, by 2.40 ± 0.49% for viability (P > 0.05), by 0.30 ± 9.92% for subjective motility (P > 0.05) and by 5.70 ± 6.07% for progressive motility (P > 0.05). We suggest that Ringer solution could be used for a short term storage (1–24 h) of equine epididymal semen at a 4 °C temperature.

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.

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.

Preservation of Epididymal Stallion Sperm in Liquid and Frozen States: Effects of Seminal Plasma on Sperm Function and Fertility

Three separate experiments were conducted to improve preservation of stallion epididymal sperm. In the first one, two different cooling extenders (Kenney and Gent) were compared. Sperm viability and motility patterns were assessed in 10 different epididymal sperm samples after 0 hours, 24 hours, 48 hours, 72 hours, and 96 hours of preservation at 4°C. No significant differences were observed in any of the evaluated parameters either between extenders or throughout the storage period. The second set of experiments was designed to determine whether supplementing thawing medium (INRA Freeze) with seminal plasma had any impact on the quality of frozen-thawed epididymal sperm. Ten epididymal frozen-thawed sperm samples coming from separate stallions were used and different functional parameters (sperm membrane integrity and lipid disorder, motility, intracellular Ca²⁺ levels, and intracellular concentrations of peroxides and superoxides) were evaluated after incubation with or without 50% seminal plasma. Supplementing thawing medium with seminal plasma had no impact on sperm function and survival. The third experiment was an in vivo study. Twenty-five mares were inseminated with epididymal frozen-thawed sperm and seminal plasma, and 21 were bred with epididymal frozen-thawed sperm only. Pregnancy rates obtained for mares artificially inseminated with epididymal frozen-thawed sperm and seminal plasma were significantly (P < .05) higher than those observed when seminal plasma was not infused (64% vs. 19%). Taken together, our data indicate that the quality of epididymal stallion sperm can be maintained at 4°C for up to 96 hours. In addition, not only does supplementing frozen-thawed epididymal sperm with seminal plasma have any damaging effect on their quality but it may also improve pregnancy rates after artificial insemination.

Effects of Different Freezing Protocols on Motility, Viability, Mitochondrial Membrane Potential, Intracellular Calcium Level, and DNA Integrity of Cryopreserved Equine Epididymal Sperm

The aim of the present study was to evaluate the effect of different freezing procedures on sperm motion, viability, the acrosome status, mitochondrial membrane potential (MMP), intracellular calcium content, and DNA integrity on epididymal stallion sperm. Therefore, the sperm of 10 healthy stallions was harvested by retrograde flushing after testectomy, diluted with a semen extender containing defined milk proteins and a freezing extender containing egg yolk and glycerol and frozen according to 4 different protocols, using a programmable freezer and a floating rack performing a slow (processes 1 and 2) or a fast cooling rate (processes 3 and 4, respectively). Post-thaw total motility and slow sperm values were lower when using process 4 compared with processes 1 and 2 (P < .05) after 1 hour of incubation. Progressive motility was lower in process 4 compared with process 1 immediately after thawing and after 1 hour of incubation (P < .05). The amount of rapid sperm was lower when using process 4 compared with process 1 immediately after thawing (P < .05). After 1 hour of incubation, the amount of rapid sperm was lower when using process 4 compared with processes 1 and 2 (P < .05). Higher values for viable sperm were seen in processes 1 and 2 compared with process 4 (P < .05) after 1 hour of incubation. Immediately after thawing, more viable sperm with high MMP (hMMP) were observed when using process 3 compared with process 2 (P < .05). After 1 hour of incubation, a significantly higher amount of viable hMMP sperm were detected when using processes 1 and 2 compared with process 4 (P < .05). Process 2 yielded a lower percentage of sperm containing low calcium (lCa) than process 3 immediately after thawing (P < .05). After 1 hour of incubation, the lowest amount of lCa sperm was observed using process 4 (P < .05). The subpopulation of viable/hMMP/lCa sperm was higher when using process 3 compared with process 2 immediately after thawing (P < .05). After 1 hour of incubation, the lowest amount of this subpopulation was detected in process 4 (P < .05). The DNA integrity was similar in all groups. In conclusion, a slow cooling rate with a controlled rate freezer resulted in best sperm quality after thawing. Using a floating rack in nitrogen vapor as an alternative to a programmable freezer, equilibration in a cooled environment is advantageous.