Action of swim-up and caffeine on equine frozen sperm

Cryopreservation of equine semen is crucial to semen commercialization. However, it reduces sperm motility and longevity. Thus, sperm selection methods and addition of motility-activating substances to sperm, such as caffeine, may improve sperm quality of equine frozen semen. The objective of the current work was to evaluate the effects of caffeine on recovery and quality parameters of frozen-thawed sperm subjected to swim-up selection to be used in intracytoplasmic sperm injection (ICSI) in assisted reproductive techniques. Stallion semen were frozen and after thawing different caffeine concentrations were added to the samples performing four treatments control (no caffeine), 3, 5, and 7.5 mM caffeine. Sperm kinematic and motility were assessed by computer-assisted sperm analysis (CASA). Then, the four treated samples were submitted to the swim-up sperm selection, and the number of recovered sperm and morphology were evaluated at four times 20, 40, 60, and 80 min. The swim-up increased the recovery proportion of normal morphology sperm without (80.1±1%) or with caffeine addition (3mM: 81.2±1%, 5mM: 79.9±1% and 7.5 mM 78.9±1%) compared to the thawed semen (70±2%). However, the addition of 5 mM caffeine induced an increase in sperm motility (38.9±2.8 vs. 32.6±3.4%, P<0.05), and sperm recovery after swim-up (7.9x10⁶ vs. 3.4x10⁶ sperm/ml, P<0.05) compared to the control. The addition of 5 mM caffeine to frozen-thawed equine semen before swim-up selection improved sperm motility and increased the sperm recovery rate while not decreasing the percentage of morphologically normal sperm. Thus, caffeine addition to frozen-thawed equine semen before swim-up selection has potential clinical application in improving sperm quality for use in ICSI.

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.

L-carnitine added to post-thawed semen acts as an antioxidant and a stimulator of equine sperm metabolism

The objective of this study was to enhance the in vitro sperm quality and in vivo fertility of frozen-thawed equine semen by the addition of l-carnitine (LC) to post-thawed semen. Different concentrations of LC were added to thawed samples to obtain four treatments control and 0.5, 1 and 2 mM LC. In the in vitro experiments, sperm motility and kinematics, membrane integrity and intracellular calcium ion concentration ([Ca²⁺ ]_i ) were investigated, and the antioxidant bioactivity of LC was assessed by measuring hydrogen peroxide and nitrite concentrations (NO₂ ^- ). The fertility rate was assessed via the artificial insemination of mares. The treatment with 1 mM LC increased sperm [Ca²⁺ ]_i (60.6 ± 0.05 AU), reduced nitrite concentration (39.1 ± 14.9 µM/µg protein), increased the sperm straightness percentage (STR: 78.3 ± 5.3%) and increased the pregnancy rate (75%) as compared to the control ([Ca²⁺ ]_i 48.4 ± 0.05 AU, NO₂ ^- concentration 63.1 ± 14.4 µM/µg protein, STR 67.5 ± 7.9%, 12.5% pregnancy rate, p < 0.05). These results suggest that 1 mM LC acts as an antioxidant and stimulator of sperm metabolism in post-thawed equine semen, increasing the fertility rate. Thus, addition of LC might be an alternative to improve the fertility of poor quality post-thawed equine semen.

Does Coenzyme Q10 Exert Antioxidant Effect on Frozen Equine Sperm?

During semen cryopreservation, the sensitivity of equine sperm to oxidative stress is increased by the eliminated seminal plasma. Thus, antioxidant addition to the semen extender can be helpful to the sperm survival after freezing and thawing. This work aimed to test whether coenzyme Q10 (CoQ10) added in different concentrations to the INRA 82 freezing extender has antioxidant function on equine sperm to improve its fertilizing ability. Semen samples from five stallions were frozen with the extenders: (T1) INRA 82, control, (T2) T1+ 5 μM CoQ10, (T3) T1+ 25 μM CoQ10, and (T4) T1+ 50 μM CoQ10. After sample thawing, sperm motility and kinetics characteristics were evaluated using a computer-assisted sperm analysis and sperm membrane functionality and integrity were evaluated with a hypo-osmotic swelling test and an epifluorescence microscopy, respectively. The nitrite (NO₂^-) and hydrogen peroxide (H₂O₂) concentrations of the semen samples were measured with spectrophotometry. There was no difference on the sperm characteristics among all treatments (P > .05). However, the 25 μM CoQ10 (T3) decreased NO₂^- concentration (6.7 ± 2.2 μM/μg protein) compared with the treatments T1, T2, and T4 (64.3 ± 3.7, 59.4 ± 5.3, 45.1 ± 8.6 μM/μg protein), respectively, as well H₂O₂ concentration (1.8 ± 0.3 μM/μg protein) compared with the control (4.6 ± 0.4 μM/μg protein) and 5 μM CoQ10 treatments (4.8 ± 0.2 μM/μg protein, P < .05). In conclusion, 25 μM CoQ10 plays a significant role as antioxidant to the frozen equine sperm, decreasing NO₂^- and H₂O₂ concentrations. Thus, its addition to the INRA 82 freezing extender may be beneficial to the fertilizing ability of equine semen.

Is the protective effect of egg yolk against osmotic and cryogenic damage on dog spermatozoa dose-dependent?

Egg yolk (EY) is conventionally used to reduce sperm cryodamage, however, there has not be evaluation of whether there is a dose-dependent effect with inclusion of EY in semen extender. To enhance the knowledge about the protective effect of EY during cryopreservation of dog semen, a specific study was designed to evaluate the dose-dependent protection of the EY against osmotic and cryogenic damage of dog sperm. In the first experiment, sperm stored in an extender that contained graded EY concentrations (0 %, 5 %, 10 %, and 20 %) were diluted with hypo- or hyper-osmotic solutions (final osmolality of 75, 150, 300, 500, 1000 mOsm/kg). Results from sperm kinetic, membrane integrity (MI), mitochondrial activity, and normal morphology evaluations indicated osmotic stress has especially marked effects on the kinetic capacity of spermatozoa, however, there were no direct effects on mitochondrial activity. In both hypo- and hyper-osmotic conditions, EY had a protective effect regardless of concentration. In the second experiment, semen samples were diluted in extenders at increasing EY concentrations (0 %, 5 %, 10 %, and 20 %) and cryopreserved. Effects on sperm kinetics, membrane and acrosome integrity and mitochondrial membrane potential indicated there was improved sperm viability after thawing when the EY concentration was 5 % and 10 %, and lesser viability when it was 20 %. These results indicate, for the first time, that EY reduces osmotic and cryogenic damage when used at 5 % or 10 % concentrations, and that these concentrations can be used to protect dog spermatozoa more effectively than the conventionally used concentration (20 %).

A comparison of semen diluents on the in vitro and in vivo fertility of liquid bull semen

The aim of this study was to assess the effect of semen diluent on calving rate (CR) following artificial insemination with liquid bull semen stored for up to 3 d postcollection. In experiment 1, the effect of storing liquid semen maintained at a constant ambient temperature in 1 of 7 different diluents [Caprogen (homemade), OptiXcell, BioXcell, BullXcell, INRA96, NutriXcell, or AndroMed (all commercially available)] on total and progressive motility was assessed on d 0, 1, 2, and 3 postcollection. In experiment 2, the field fertility of liquid semen diluted in Caprogen, BioXcell, or INRA96 and inseminated on d 1, 2, or 3 postcollection was assessed in comparison to frozen-thawed semen (total of n = 19,126 inseminations). In experiment 3, the effect of storage temperature fluctuations (4 and 18°C) on total and progressive motility following dilution in Caprogen, BioXcell, and INRA96 was assessed on d 0, 1, 2, and 3 postcollection. In experiment 1, semen stored in Caprogen, BioXcell, and INRA96 resulted in the highest total and progressive motility on d 1, 2, and 3 of storage compared with OptiXcell, BullXcell, NutriXcell, and AndroMed. In experiment 2, an effect of diluent on CR was found as semen diluted in BioXcell had a lower CR on d 1, 2, and 3 of storage (46.3, 35.4, and 34.0%, respectively) in comparison with Caprogen (55.8, 52.0, and 51.9%, respectively), INRA96 (55.0, 55.1, and 52.2%, respectively), and frozen-thawed semen (59.7%). Effects were found of parity, cow fertility sub-index, as well as the number of days in milk on CR. In experiment 3, when the storage temperature of diluted semen fluctuated between 4 and 18°C, to mimic what occurs in the field (nighttime vs. daytime), BioXcell had the lowest total and progressive motility in comparison to Caprogen and INRA96. In conclusion, diluent significantly affected sperm motility when stored for up to 3 d. Semen diluted in INRA96 resulted in a similar CR to semen diluted in Caprogen and to frozen-thawed semen, whereas that diluted in BioXcell resulted in a decreased CR. Consistent with this finding, semen diluted in BioXcell was less tolerant of temperature fluctuations than that stored in Caprogen or INRA96. Given that it can be used directly off the shelf, INRA96 may be a suitable alternative to Caprogen for the storage of liquid bull semen.

Cryopreservation of stallion spermatozoa using different cryoprotectants and combinations of cryoprotectants

The present study investigates the effects of five cryoprotectants (CPAs) and cryoprotectant combinations on the post-thaw total motility, progressive motility, viability, mitochondrial membrane potential and acrosome integrity in stallion spermatozoa. In Experiment 1, the objective was to compare the impact of different concentrations (2.5%, 3.5% and 5%) of a single CPA, including glycerol (Gly), ethylene glycol (EG), dimethyl sulphoxide (DMSO), methyl formamide (MF), and dimethylformamide (DMF) for stallion spermatozoa cryopreservation. In Experiment 2, two or more CPAs were used to assess whether this improved post-thaw spermatozoa quality. Gly, MF and DMF, were used to prepare seven combinations of freezing extender with different mixtures of cryoprotectant, and the 3.5% Gly, MF and DMF were used as a control group. The results show that post-thaw total motility, progressive motility, viability, and mitochondrial membrane potential for all concentrations of EG and DMSO were less than the 3.5% and 5% Gly and MF and 2.5% and 3.5% DMF (P<0.05). Use of the 3.5% concentration resulted in the greater post-thaw total motility and progressive motility than the 2.5% and 5% concentrations for all CPAs. The results for the use of different combinations of cryoprotectant indicate there are differences in progressive motility and viability. The viability with the use of Gly(2/3)+MF(1/3) was 44.65% and was greater than the Gly(1/3)+MF(1/3)+DMF(1/3) (30.96%), MF(2/3)+DMF(1/3) (35.05%), Gly (32.21%) and MF(33.76%) (P<0.05). The progressive motility with the use of the MF(2/3)+Gly(1/3) combination was 36.0% and was greater than in the DMF (25.0%) and MF(2/3)+DMF(1/3) (22.7%) (P<0.05). These results suggest that using the appropriate cryoprotectant combination instead of a single cryoprotectant can improve horse spermatozoa cryopreservation.

Interaction of milk proteins and Binder of Sperm (BSP) proteins from boar, stallion and ram semen

BACKGROUND

Mammalian semen contains a family of closely related proteins known as Binder of SPerm (BSP proteins) that are added to sperm at ejaculation. BSP proteins extract lipids from the sperm membrane thereby extensively modifying its composition. These changes can ultimately be detrimental to sperm storage. We have demonstrated that bovine BSP proteins interact with major milk proteins and proposed that this interaction could be the basis of sperm protection by milk extenders. In the present study, we investigated if homologous BSP proteins present in boar, stallion and ram seminal plasma display a similar affinity for the milk proteins in order to assess whether the mechanism of sperm protection by milk for these species could be general.

METHODS

Skim milk was incubated with seminal plasma proteins (boar, stallion and ram), chromatographed on a Sepharose CL-4B column and protein fractions were analyzed by immunoblotting.

RESULTS

Boar, stallion and ram BSP proteins displayed affinity for a milk protein fraction (F1) mainly composed of α-lactalbumin, β-lactoglobulin, and κ-casein. They also had affinity for another milk protein fraction (F2) composed mostly of casein micelles. However, stallion BSP showed higher affinity for the fraction (F1).

CONCLUSIONS

These results further extend our view that the association of BSP proteins with milk proteins could be a general feature of the mechanism of mammalian sperm protection by milk to prevent detrimental effect of prolonged exposure of sperm to seminal plasma.

Liposomes as an alternative to egg yolk in stallion freezing extender

Egg yolk is normally used as a protective agent to freeze semen of equine and other species. However, addition of egg yolk in extenders is not without disadvantages and the demand to find cryoprotective alternatives is strong. The objective of this study was to test the cryoprotective capacities of liposomes composed of egg yolk phospholipids. Two experiments were conducted: 1) the first to determine the optimal composition and concentration of liposomes to preserve post-thaw motility and membrane integrity of spermatozoa; 2) the second to assess in vivo the cryoprotective capacities of these liposomes. In Experiment 2, post-thaw motility and membrane integrity of spermatozoa were also analyzed. Experiment 1 demonstrated that liposomes composed of phospholipids E80 (commercial lecithins from egg yolk composed mainly of phosphatidylcholine and phosphatidylethanolamine) and of Hank's salts-glucose-lactose solution (E80-liposomes) were the most efficient in preserving post-thaw motility. The optimal concentration was 4 % (v/v). In Experiment 2, fertility rate after artificial insemination of semen frozen with E80-liposomes was 55 % (22/40) compared with 68 % (27/40) with the control extender containing egg yolk (EY) (p = 0.23). Post-thaw motility parameters were higher with EY than with E80-liposomes (p < 0.0001). For post-thaw membrane integrity no difference was observed between the two extenders (p = 0.08). Liposomes composed of egg yolk phospholipids appeared to be a promising alternative to replace egg yolk in semen freezing extenders in equine species.