Effect of buffering systems on post-thaw motion characteristics, plasma membrane integrity, and acrosome morphology of buffalo spermatozoa

Cryopreservation Techniques for Ram Sperm

Germplasm storage and transportation in artificial insemination (AI) and other advanced technologies are facilitated by cryopreservation. In reproduction, the cryopreservation of sperm allows it to be transported across vast distances and used even after the sire's death. However, the technique of cryopreservation might damage sperm and limit their activity. Several cryobiological investigations have reported that the integrity of the sperm membrane is frequently involved in the physical and biological elements that affect sperm survival at low temperatures during the cryopreservation process. However, successful cryopreservation of ram sperm is still a work in progress because a considerable percentage of sperm do not survive the freezing and thawing process. Sperms are destroyed during cryopreservation of semen due to varying concentrations of cryoprotective chemicals and if semen is not cooled at optimal cooling rates. Hence, it is crucial to know the optimum cooling rates with freezing and thawing protocols for maximum recovery of viable and functional sperm cells for a successful cryo-freezing of ram spermatozoa. Therefore, the current study compiled and compared the research on the impact of different cryopreservation procedures, cooling rates, equilibration time, and thawing protocols on post-thaw ram semen quality.

Impact of antibiotics on spermatozoa quality and bacterial load of chilled-stored camels (Camelus dromedarius) semen

This experiment was conducted to assess the effect of different antibiotics in tris-fructose egg yolk-based diluent on bacterial load and sperm quality of dromedary camels during processing and cold storage. Ten semen ejaculates were collected from five male dromedary camels. Each sample was fractioned into four equally divided aliquots and diluted in one of four tris-fructose egg yolk. The first extender contained no antibiotic (NC). The second extender included streptomycin sulphate (1000 μg/ml) and benzyl penicillin (1000 IU/ml) (SP). The third extender was supplied with 250 μg/ml gentamicin sulphate (Gent). The fourth extender contained 500 μg/ml gentamicin sulphate,100 μg/ml tylosin tartrate, 300 μg/ml lincomycin hydrochloride and 600 μg/ml spectinomycin hydrochloride (GTLS). After dilution, the extended semen samples were cooled to 5 °C within 2 h and finally stored at 5 °C for 72 h. Microbial concentration, motility of spermatozoa, live spermatozoa, plasma membrane and acrosome integrity percentages were evaluated just after dilution at 35 °C, 0, 24, 48 and 72 h from the start of cooling to 5 °C. The results revealed that the diluent containing gentamicin had significantly (P<0.05) maximum motility percentage at the different examination intervals. The pattern of live spermatozoa percentage was varied between the different treatments at different examination intervals. The diluent supplied with Gent was distinguished with a significant peak percentage (P<0.05) of swelled spermatozoa among the other antibiotics supplied diluents. The number of colony-forming units isolated from the semen samples kept in diluent containing no antibiotics was significantly (P<0.05) higher than that isolated from the diluents supplemented with antibiotics. In conclusion, the semen diluents fortified with gentamicin generally keep the motility, acrosomal and plasma membrane integrity and live spermatozoa for 72-h preservation of dromedary semen.

Resveratrol supplementation into extender protects against cryodamage in dog post-thaw sperm

Antioxidants have multiple protective roles in a variety of cells and thus can be used to protect sperm against cryo-damage during freezing, which affects fertility. The antioxidant resveratrol (3,5,4-trihydroxytrans-stilbene; RSV) has been reported to protect the animal sperm during cryopreservation, including human sperm. In this study, we assessed the protective effects of RSV supplementation on dog sperm cryopreservation. Semen was collected from four dogs and the effect of different concentrations of RSV (0, 100, 200, and 400 µM) on post-thaw sperm quality was examined. After thawing, sperm motility was assessed using computer-aided sperm analysis, and the structural integrity of the plasma membrane, acrosome, and chromatin was examined. In addition, their mitochondrial activity and gene expression were also assessed. Dog sperm cryopreserved with 200 µM RSV showed significant improvement in post-thaw sperm motility and viability compared with that of the control group (P<0.05). Moreover, RSV-supplemented samples showed significantly higher numbers of sperm with an intact plasma membrane, active mitochondria, and structural integrity of acrosomes and chromatin than that of control samples (P<0.05). Furthermore, gene expression showed that RSV supplemented samples showed lower expression of pro-apoptotic (BAX), reactive oxygen species (ROS) modulator oxidative stress-related (ROMO1) and 8-oxoguanine DNA glycosylase 1 (OGG1) whereas higher expression levels of anti‐apoptotic (BCL2), protamine-2 (PRM2), protamine-3 (PRM3) and sperm acrosome‐associated 3 (SPACA3) genes than control. Our results suggest that RSV, at its optimum concentration, can be efficiently used as an antioxidant in the cryopreservation of dog sperm.

The effects of metabolic substrates glucose, pyruvate, and lactate added to a skim milk-based semen extender for cooled storage of stallion sperm

Under in vitro conditions, stallion sperm might preferentially use energy substrates that primarily undergo mitochondrial metabolism. The present study sought to determine the effects of glucose, pyruvate, lactate, or their combinations on the quality of stallion sperm subjected to cooled storage at different temperatures, when using a skim milk-based semen extender. In Experiment 1, no substrate (Control), glucose (40 mM; Glu-40), pyruvate (2 mM, 19.8 mM; Pyr-2, Pyr-19), lactate (2 mM, 19.8 mM; Lac-2, Lac-19, respectively), or their combinations (G/P/L-2 or G/P/L-19, respectively) were added to a milk-based extender and their effects were determined on motion characteristics, viability/acrosomal intactness (VAI), lipid peroxidation status (VLPP), and DNA integrity (COMP_α-t) of sperm incubated for 1 h at 37 °C, or sperm stored for 24 h at either 10 or 20 °C. At any period and temperature tested, Glu-40, G/P/L-2, and G/P-L-19 resulted in similar motion characteristics (P > 0.05) but were higher than that of other treatment groups (P < 0.05). Mean VAI was highest in Glu-40 (P < 0.05). Mean VLPP was highest in G/P/L-2 and G/P/L-19 groups (P < 0.05), and mean COMP_α-t was lowest in Control, Glu-40, G/P/L-2 and G/P/L-19 groups (P < 0.05). All measures of sperm quality were higher in semen stored at 10 °C than 20 °C (P < 0.05). In Experiment 2, increasing concentrations of either pyruvate or lactate (Pyr-40, Lac-40 or Pyr-80, Lac-80) were added to the extender as energy substrates and compared to glucose (40 mM), following storage for 72 h at either 10 or 20 °C. Groups Glu-40 and Pyr-40 yielded similar sperm motion characteristics and VAI, while VLPP and COMP_α-t were reduced in these treatment groups, as compared to Pyr-80, Lac-40, and Lac-80 (P < 0.05). All measures of sperm quality were higher in semen stored at 10 °C vs 20 °C (P < 0.05). This study demonstrates that at storage temperatures of 10 or 20 °C, stallion sperm quality is optimized by the presence of glucose in a skim milk-based semen extender. The addition of substrates that readily support oxidative phosphorylation (i.e., pyruvate or lactate) did not improve the quality of stallion sperm over that of glucose alone and resulted in deleterious effects on sperm quality over time. These effects appeared to be associated with oxidative stress. Use of pyruvate (40 mM) as an alternative energy substrate to glucose generally yielded similar results to that of glucose when sperm were stored at 10 °C only.

Melatonin supplementation improved cryopreserved Thai swamp buffalo semen

The production of reactive oxygen species (ROS) during cryopreservation process impairs the sperm characteristics and fertilizing ability. However, melatonin, an antioxidant, could protect spermatozoa against this cell damage during cryopreservation. Therefore, we attempted to evaluate whether the melatonin supplementing in the semen extender could improve the sperm quality of swamp buffalo during cryopreservation. The semen collected from six swamp buffalo bulls were diluted with tris-citrate egg yolk extender supplementing with 0, 0.1, 0.5, 1.0, 2.0 and 3.0 mM of melatonin. The parameters of sperm viability and motility were evaluated using computer-assisted semen analyser (CASA) after cryopreservation on days 1, 7, 15 and 30. The group supplemented with 1.0 mM melatonin exhibited the higher viability after cryopreservation on days 1, 7, 15 and 30 with 58.346 ± 2.1^a , 57.586 ± 2.0^a , 55.082 ± 1.8^a and 55.714 ± 1.8^a , respectively, and showed the best results of motility parameters. However, higher concentration of melatonin at 3.0 mM impaired all the parameters. In conclusion, the addition of melatonin at 1 mM to semen extender could exert the best protection against sperm damage in swamp buffalo bull during cryopreservation.

The effect of astaxanthin supplementation on the post-thaw quality of dog semen

Astaxanthin is a member of the carotenoid family well known for its anti-cancer, anti-diabetic, anti-inflammatory and antioxidant nature. This study was designed to investigate the effects of astaxanthin supplementation of the extender (buffer 2) on post-thaw dog semen quality. Semen from four healthy dogs was collected by digital manipulation twice a week. The ejaculates were pooled, washed, divided into four equal aliquots, diluted with the extender supplemented with different concentrations of astaxanthin (0, 0.5, 1 and 2 µM) and cryopreserved. The results showed that 1 µM astaxanthin was the optimum concentration that led to significantly higher (p < .05) post-thaw motility, kinematic parameters and viability than the other groups. In comparison with the control group, sperm samples supplemented with 1 µM astaxanthin showed significantly higher (p < .05) sperm counts with intact membranes (55.7 ± 0.6% vs. 51.3 ± 0.9%), intact acrosome (58.4 ± 0.7% vs. 53.5 ± 0.6%), active mitochondria (54.9 ± 0.5% vs. 42.6 ± 0.6%) and normal chromatin (67.6 ± 0.9% vs. 61.7 ± 0.6%). Furthermore, astaxanthin-supplemented samples showed significantly lower expression levels (p < .05) of pro-apoptotic (BAX), oxidative induced DNA damage repair (OGG1), oxidative stress-related (ROMO1) genes and higher expression levels of anti-apoptotic (BCL2), and sperm acrosome-associated (SPACA3) genes compared to the control. Thus, supplementation of 1 µM astaxanthin in semen extender results in improved freeze-thaw sperm quality of the dog.

Evaluation of pigeon egg yolk for post thaw quality, enzyme leakage and fertility of buffalo (Bubalus bubalis) bull spermatozoa

Egg yolk is used as a cryoprotectant in semen preservation. However, its composition varies according to the species which may influence its effectiveness during the freeze-thaw process. Therefore, study was conducted to identify the optimum level of pigeon egg yolk (PEY) in Tris citric acid (TCA) extender for freezability and in vivo fertility of buffalo semen. Semen was collected at weekly intervals for a period of three weeks (replicates) from 6 Nili Ravi buffalo bulls (2 ejaculates/bull/replicate) and diluted with TCA extender (50 × 10⁶ motile spermatozoa ml^-1) containing 5%, 10%, 15% and 20% PEY or 20% CEY (control) and cryopreserved. Post-thaw sperm quality and extracellular enzymes leakage was assessed after thawing. Sperm motility, plasma membrane integrity, livability and viability was significantly higher in extenders containing 10% and 15% PEY compared to 5% PEY, 20% PEY or 20% CEY (controls). A dose-dependent decrease was recorded in the chromatin damage for the PEY, being lowest for the 15% and 20% PEY which was significantly less compared to controls (20% CEY). The extracellular GOT and LDH leakage was significantly lower (P < 0.05) in extender containing 10% and 15% PEY compared to the controls. Semen collected from 2 bulls, cryopreserved in extenders containing 15% PEY or 20% chicken egg yolk was assessed for fertility after artificial inseminations. A total of 400 buffaloes were inseminated (100 inseminations/extender/bull). The overall fertility rate was significantly higher (P < 0.05) with semen cryopreserved in extender containing 15% PEY (56%) compared to 20% CEY (42%; controls). In conclusion, pigeon egg yolk at 15% offers advantages over 20% chicken egg yolk in terms of in vitro post-thaw semen quality and in vivo fertility of buffalo.

Bull Fertility and Its Relation with Density Gradient Selected Sperm

Background

Sperm selection method is usually used to collect these cells for in vitro-assisted reproduction. Few studies reported the relationship of in vivo fertility and semen parameters after sperm selection; hence, the present study attempted to assess different semen parameters after post-thaw or sperm selection, using density gradient separation BoviPure®, to predict in vivo fertility.

Materials and Methods

In this experimental study, frozen semen quality of four Montbeliarde bulls were assessed after post-thaw (PT) or after sperm selection (SSp), using density gradient separation BoviPure®, to predict the fertility rate in vivo. In addition to PT or SSp, semen was examined for concentration, motility, morphology abnormalities, viability, acrosome and plasma membrane integrities. Fertility was measured as non-return rates within 56 days after the first insemination (NRR) or as corrected NRR, expressed as CNRR, to the factors influencing fertility using linear mixed model. Non-parametric Kruskal-Wallis test was performed to compare semen parameter variables. Fertility rates were compared using Chi-square test. Pearson correlation analysis was used to test the relationship between CNRR and semen parameters. Data was analysed using SPSS package program, version 21.0.

Results

Most of the examined bulls exhibited a high fertility rate (3/4 bulls, 62.1- 81.8% for NRR or 67.2-98.5% for CNRR). Fertility rate, expressed as CNRR, was significantly related to semen parameters after SSp, but not after PT. Thus, CNRR was increased with decrease of total motility, progressive spermatozoa and abaxial implantation frequencies after SSp (r=-0.999, P=0.001; r=-0.990, P=0.010; r=-0.988, P= 0.012, respectively); while, CNRR was decreased with decrease of SSp immotile spermatozoa (r=+0.995, P=0.005), underlying that maximal limit of determined immotile spermatozoa is 47%.

Conclusion

High frequencies of total and progressive motility spermatozoa, and abaxial implantation in gradient selected sperm appear to be not favorable for fertility in vivo.

Cholesterol-loaded cyclodextrins prevent cryocapacitation damages in buffalo (Bubalus bubalis) cryopreserved sperm

The aim of this study was to investigate the effect of cholesterol-loaded cyclodextrins (CLC) on motility, viability, capacitation status, and in vivo fertility of buffalo frozen-thawed sperm. After the initial semen assessment, buffalo sperm were diluted in BULLXcell extender containing 0- (control), 1.5-, and 3-mg/mL CLC and cryopreserved. At thawing, sperm motility was evaluated by phase contrast microscopy, and viability-capacitation status was assessed by Hoechst 33258-chlortetracycline (CTC) assay. Capacitation status was also evaluated by an indirect immunofluorescence assay to localize phosphotyrosine-containing proteins. Moreover, buffaloes were artificial inseminated to assess the in vivo-fertilizing potential of CLC-treated semen. No differences among control, 1.5-, and 3-mg/mL CLC-treated groups were recorded in both sperm motility (66.5 ± 5.6, 68.8 ± 4.8, and 68.8 ± 4.8, respectively) and viability (86.5 ± 1.9, 87.6 ± 1.5, 88.4 ± 2.3, respectively). However, the extender supplementation with CLC significantly reduced sperm cryocapacitation. Indeed, CLC treatment decreased (P < 0.01) the proportion of sperm showing the CTC pattern B (capacitated sperm) compared with the control (69.6 ± 3.4, 37.8 ± 1.5, and 51.3 ± 4.7, respectively, with 0, 1.5-, and 3-mg/mL CLC; P < 0.01). Furthermore, the percentage of sperm displaying tyrosine-phosphorylated pattern EA (i.e. high capacitation level) was reduced (P < 0.01) in both CLC-treated groups (10.8 ± 3.3 and 5.6 ± 1.6, respectively, with 1.5- and 3-mg/mL CLC) compared with the control (37.3 ± 6.9), reaching values similar to those recorded in fresh semen (11.0 ± 3.5). In addition, treating sperm with 3-mg/mL CLC increased (P < 0.01) the percentage of nonfluorescent (pattern NF), i.e., non-capacitated sperm (41.8 ± 3.6) compared with fresh semen (11.0 ± 6.9). No differences were recorded in pregnancy rates at 60 days post-artificial insemination among control, 1.5- and 3-mg/mL CLC groups (59.7%, 65.6%, and 56.9%, respectively). In conclusion, CLC treatment of buffalo sperm strongly decreases sperm cryocapacitation damages, without affecting the in vivo fertilizing capability.

Effect of cooling rate and equilibration time on pre-freeze and post-thaw survival of buck sperm

Survival of buck sperm is affected due to duration and temperature of stages of refrigerated or frozen storage. This study investigated interactive effect of cooling rates (moderate; MC and rapid cooling; RC); and equilibration times (0, 2, 4 and 8h) on survival before freezing at 4°C and post-thaw quality of buck sperm. Semen was collected (three Beetal bucks; replicates=6), pooled and diluted with Tris-citrate extender. Pooled semen samples were subjected to either RC (-2.2°C/min) or MC (-0.3°C/min) from 37°C to 4°C in separate aliquots and further equilibrated at 4°C for 8h. Semen was frozen using standard procedure after completion of each equilibration period i.e. 0, 2, 4 and 8h. Semen was evaluated for motility, viability, plasma membrane integrity (PMI) and normal apical ridge (NAR) before freezing and after thawing. The survival time (time for survival above threshold limit i.e. 60%) at 4°C, of motility and PMI was observed 5 and 6h respectively in RC group while >8h in MC group. Rate of decline (slope) in motility and viability was higher (P<0.05) in RC overtime during equilibration at 4°C while PMI and NAR declined at equal rate in both cooling groups. Post-thaw motility and NAR were higher (P<0.05) in MC when equilibrated for 2-8h while viability and PMI of RC was observed equal to MC group. In conclusion, survival of buck sperm is higher when cooled with moderate rate. However, RC can maintain post-thaw sperm viability and PMI equal to MC when equilibrated for 2-8h. The methods should be explored to maintain motility and NAR during rapid cooling of buck sperm.

Relative efficacy of egg yolk and soya milk-based extenders for cryopreservation (-196°C) of buffalo semen

Aim:

The aim was to compare commercially available soybean milk-based extenders, viz. Bioxcell^® and Optixcell^® (IMV, France) with standard Tris-citrate-fructose-egg yolk-glycerol (TFYG) extender for cryopreservation of buffalo semen.

Materials and Methods:

Semen was collected twice a week in artificial vagina from six sexually mature, 4-6 years old, healthy breeding bulls of Surti buffalo breed. In all 48 qualifying ejaculates (8 per bull) having initial motility >70% were split into three equal aliquots and were diluted (at 34°C keeping 100×10⁶ sperm ml⁻¹) in TFYG, Bioxcell and Optixcell extenders. The French mini straws filled from each aliquot were gradually cooled to 4-5°C, equilibrated at 4°C for 4 h and frozen in liquid nitrogen 2 vapor using programmable biofreezer. Just before freezing (post-equilibration) and 24 h after frozen storage, the samples were evaluated for various sperm quality parameters using standard protocols. Frozen semen straws were thawed in a water bath at 37°C for 30 s. The post-thaw incubation survival (37°C for 1 h) was assessed through motility rating at 0, 30 and 60 min of incubation.

Results:

The mean percentages of prefreeze sperms in TFYG, Bioxcell and Optixcell extenders in terms of progressive motility (69.48±0.37, 68.02±0.49, 70.94±0.38), viability (79.21±0.39, 77.38±0.48, 81.58±0.38), total abnormalities (7.90±0.14, 8.60±0.16, 7.08±0.15), intact acrosome (89.54± 0.18, 88.58±0.22, 90.52±0.21) and hypoosmotic swelling (HOS) reactivity (67.96±0.32, 65.65±0.42, 70.23±0.37) varied significantly (p<0.05) between extenders. Similar pattern of significant (p<0.05) variations between these extenders for post-thaw sperm progressive motility (47.71±0.79, 44.38±0.85, 49.90±0.90), viability (57.19±0.79, 53.85±0.84, 59.67±0.91), total abnormalities (12.33±0.17, 12.75±0.21, 11.27±0.18), intact acrosome (76.83±0.23, 75.90± 0.27, 78.50±0.25) and HOS reactivity (45.02±0.84, 42.31±0.82, 47.81±0.90) was also observed for TFYG, Bioxcell and Optixcell extenders. The recently launched improved soybean milk-based extender Optixcell excelled the older Bioxcell extender and even standard TFYG in respect of some of the sperm quality parameters.

Conclusion:

The advantages of soy lecithin-based bovine semen extenders over egg yolk regarding sanitary issues are unquestionable but still egg yolk-based semen extenders are widely used because of the cost factor and good in vivo fertility results.

Changes in motility, morphology, plasma membrane and acrosome integrity during stages of cryopreservation of buck sperm

Changes in sperm structure and function occur during the processing of semen. The present study was designed to investigate the effect on buck sperm during different stages of semen preparation including dilution, cooling, equilibration and freeze-thawing. Semen ejaculates from three mature bucks (replicates = 5) were diluted with tris-citric acid egg yolk glycerol extender at 37 ºC, cooled to 4 ºC over 90 min, equilibrated at 4 ºC for 2 h, transferred to 0.5 mL straws, placed in nitrogen vapour, frozen and thawed and then analysed. Sperm samples were assessed for percentage motility, acrosomal and plasma membrane integrity, live sperm, and morphology after dilution, cooling, equilibration and thawing. Mean percentage motility after dilution (86.0 ± 1.4%) was reduced significantly (p &lt; 0.05) due to cooling and equilibration (77.6 ± 1.3% and 74.6 ± 1.4% respectively); furthermore, it decreased significantly (p &lt; 0.05) after freezing and thawing (42.3 ± 2.5%). Mean percentage of live sperm was higher (p &lt; 0.05) after dilution (89.3 ± 1.4%)compared with cooling (84.8 ± 1.8%) and equilibration (80.2 ± 2.5%) and further reduced (p &lt; 0.05) after freezing and thawing (56.0 ± 3.4%). Sperm morphology dropped significantly (p &lt; 0.05) from 96.4 ± 0.3% after dilution to 88.8 ± 1.3% at cooling and further decreased (p &lt; 0.05) after freezing and thawing (81 ± 1.9%). Mean percentage of sperm with normal plasma membrane after dilution (82.2 ± 1.1%) was significantly reduced (p &lt; 0.05) at cooling or equilibration (73.8 ± 1.8) and further decreased (p &lt; 0.05) after freezing and thawing (50.1 ± 2.9%). The percentage of sperm with normal acrosomes did not differ significantly due to dilution, cooling or equilibration (85.8 ± 1.7%, 83.2 ± 1.6%, 81.7 ± 1.8%) but was significantly reduced after freezing and thawing (45.2 ± 2.8%). In conclusion, frozen thawed sperm showed maximum damage to motility, morphology, plasma membrane and acrosome integrity following cooling.

Effect of cysteine and glutamine added to extender on post-thaw sperm functional parameters of buffalo bull

Amino acids seem to be crucial components for semen freezing extender due to antioxidant properties. Therefore, this study aimed to assess motility parameters, membrane integrity, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP) and DNA damage to detect the optimum concentrations of cysteine and glutamine for buffalo semen cryopreservation. Twenty ejaculates of four buffalo bulls were diluted in tris-egg yolk extender and divided into seven equal groups consisting of cysteine (5, 7.5 and 10 mmol), glutamine (10, 15 and 20 mmol) and no additive. Supplementation of 5 and 7.5 mmol cysteine and 15 mmol glutamine in cryopreservation extender significantly increased post-thaw motility and plasma membrane integrity of spermatozoa with significant reduction in intracellular ROS when compared with control groups (P < 0.05). Cysteine at 7.5 mmol concentration elevated progressive motility and MMP, compared with control (P < 0.05). No significant differences were observed for motion patterns and DNA damage of frozen-thawed buffalo spermatozoa in extender containing amino acids. The findings of this study showed that supplementation of 7.5 mmol cysteine and 15 mmol glutamine in semen cryopreservation extender has more potential to decrease intracellular ROS, and subsequently elevate motility and membrane integrity of buffalo frozen-thawed spermatozoa.

Comparison of sperm quality and DNA integrity in mouse sperm exposed to various cooling velocities and osmotic stress

The first objective was to compare sperm quality following conventional manual sperm freezing (cryovials held 1, 2, 3, and 4 cm, respectively, above liquid nitrogen (LN(2)) for 10 min, resulting in cooling velocities of approximately -14.9, -10.1, -6.6, and -5.1 °C/min, respectively), and cooling velocities of -5, -20, -40, and -100 °C/min in a programmed automated freezer, for sperm recovered from CD-1, B6129SF1, and C57BL/6NCrlBR mice. Furthermore, using these strains, as well as 129S/SvPaslco, and DBA/2NCrlBR mice, the second objective was to determine the effects on DNA integrity of sperm exposed to hyposmotic (1 mOsm/L) and hyperosmotic (2400 mOsm/L) solutions, compared to an isosmotic control (300 mOsm/L). For freezing above LN(2) or in an automated freezer, 2 cm above LN(2) and -100 °C/min, respectively, were optimal (P < 0.05-0.01), with no significant differences between these two approaches for post-thaw progressive motility, DNA integrity, and in vitro rates of fertilization and blastocyst formation. Both manual and automated freezing techniques increased post-thaw sperm DNA fragmentation (P < 0.01); the DNA integrity of post-thaw sperm was significantly affected by cooling velocity and strain background. Relative to isosmotic controls, a hyposmotic solution was more deleterious (P < 0.05-0.01) to sperm DNA integrity than a hyperosmotic solution for CD-1, B6129SF1, C57BL/6, and DBA mice (there were strain-dependent differences). In conclusion, optimization of freezing distance and cooling velocity (manual and automated freezing, respectively) were significant factors for efficient cryopreservation and re-derivation of mice from frozen-thawed sperm. Additionally, osmotically-driven volume changes in mouse sperm increased DNA fragmentation, with susceptibility affected by background strain.

Response of buffalo spermatozoa to low temperatures during cryopreservation

This is the first detailed report on the response of buffalo spermatozoa to low temperatures during freezing. The study determined the critical temperature zone for buffalo spermatozoa and developed a suitable freezing rate for this species. Semen from four Nili-Ravi buffalo bulls diluted in Tris-citric acid was frozen in a programmable freezer. Motion characteristics, plasma membrane integrity and acrosome morphology were determined at +4, 0, –5, –10, –20, –30, –40, –50, –80 and –196°C by removing semen straws from the freezer at exactly these temperatures and rewarming them at 37°C. The first statistical decline in sperm motility and lateral head displacement was observed at –40°C. For all other parameters, there was biphasic decline: for curvilinear velocity, at 0°C and –50°C; and for plasma membrane integrity and acrosome morphology, at –30°C and –50°C. In a second series of experiments, buffalo spermatozoa were frozen using slow (–10°C min–1), medium (–20°C min–1) or fast (–30°C min–1) freezing rates, between –10°C and –80°C. Freezing of buffalo spermatozoa at a rate of –30°C min–1 yielded higher post-thaw motion characteristics, plasma membrane integrity and normal acrosomes. In conclusion, different sperm characteristics respond differently at low temperatures and the freezing of buffalo spermatozoa at a higher rate ensures higher post-thaw semen quality.

Motility, acrosome integrity, membrane integrity and oocyte cleavage rate of sperm separated by swim-up or Percoll gradient method from frozen-thawed buffalo semen

Frozen-thawed semen of five buffalo bulls was used to compare efficacy of swim-up and Percoll gradient methods for separating viable spermatozoa. Sperm separated by the two methods were also tested to differentiate buffalo bulls on the basis of in vitro fertilization (IVF) rates. Recovery of motile sperm (%), increase in membrane integrity (%) and acrosome integrity (%) were compared after two sperm separation methods in experiment I, and in vitro fertilization rate (cleavage rate and cleavage index) was compared in experiment II. Swim-up separated sperm showed a higher motility (P<0.05), while percent recovery of motile sperm was higher with Percoll separation (P<0.05). Membrane integrity (%) of sperm separated with swim-up was significantly higher (P<0.05) as compared to sperm separated with Percoll gradient. Swim-up separated sperm gave a higher cleavage rate and cleavage index (P<0.001). Sperm separated by swim-up showed significant difference among the bulls in cleavage rate and cleavage index (P<0.05), while the Percoll gradient method did not. It has been concluded that separation of sperm from frozen-thawed buffalo semen by swim-up method can be more expedient for IVF in buffalo.

Duck egg yolk in extender improves the freezability of buffalo bull spermatozoa

We investigated the use of duck egg yolk (DEY), Guinea fowl egg yolk (GFEY) and Indian indigenous hen (Desi) egg yolk (IDEY) in extender for improving the post-thaw quality of buffalo (Bubalus bubalis) bull spermatozoa, and compared it with commercial hen egg yolk (CHEY; control). For this purpose, two consecutive ejaculates of semen from each of two Nili-Ravi buffalo bulls were collected on 1 day each week for 5 weeks (replicates; n=5) with artificial vagina (42 degrees C). Split pooled ejaculates, were diluted in tris-citric acid glycerol extender containing either DEY or GFEY or IDEY or CHEY at 37 degrees C. Extended semen was cooled to 4 degrees C in 2 h and equilibrated for 4 h at 4 degrees C. Cooled semen was then filled in 0.5 ml straws at 4 degrees C and frozen in programmable cell freezer. Thawing of semen was performed at 37 degrees C for 30 s. Sperm motility, plasma membrane integrity and sperm morphology (acrosome integrity, head, mid-piece and tail abnormalities) of each semen sample were assessed at 0, 3 and 6 h after thawing and incubation at 37 degrees C. Visual motility (%) and percentage of intact plasma membranes assessed at 6h post-thaw of buffalo bull spermatozoa were highest (P<0.05) due to DEY as compared to GFEY, IDEY and control. The percentage of spermatozoa with normal acrosomes at 0, 3 and 6 h post-thaw was highest (P<0.05) in DEY extender than GFEY, IDEY and CHEY. Sperm tail abnormalities (%) observed at 0, 3 and 6 h post-thaw in samples cryopreserved with freezing extender having DEY were lower (P<0.05) as compared to extender containing GFEY, IDEY and CHEY. In conclusion, DEY compared to other avian yolks in extender improves the frozen-thawed quality of buffalo bull spermatozoa.

Antagonist effect of DMSO on the cryoprotection ability of glycerol during cryopreservation of buffalo sperm

The objective of the present study was to investigate the synergistic effect of DMSO and glycerol added at various temperatures on the post-thaw quality of buffalo sperm. Pooled ejaculates from four Nili-Ravi buffalo bulls were divided into 18 aliquots and extended (1:10) in Tris-citric acid extender differing in glycerol:DMSO ratios (0:0, 0:1.5, 0:3; 3:0, 3:1.5, 3:3; and 6:0, 6:1.5, 6:3, respectively; %, v:v) either at 37 or 4 degrees C. Semen was packaged in 0.5 mL French straws and frozen in a programmable cell freezer. Thawing was performed at 37 degrees C for 50s. Post-thaw motion characteristics, plasma membrane integrity and acrosome morphology of buffalo sperm were determined using computer-assisted semen analyzer (CASA), hypoosmotic swelling (HOS) assay and phase-contrast microscopy, respectively. Glycerol (6%) in extender yielded better post-thaw sperm motility, velocities (straight-line and average path), plasma membrane integrity, and normal acrosomes (P<0.05). Post-thaw sperm motility and plasma membrane integrity declined in the presence of DMSO (P<0.01). The addition of glycerol (6%) at 37 degrees C yielded better post-thaw sperm motility, plasma membrane integrity and velocities than addition at 4 degrees C (P<0.05). In conclusion, glycerol is still an essential cryoprotectant for buffalo sperm. The addition of DMSO antagonized the cryoprotection ability of glycerol and reduced the post-thaw quality of buffalo sperm. Furthermore, 6% glycerol added at 37 degrees C, provided better cryoprotection to the motility apparatus and plasma membrane integrity of buffalo sperm.

Seasonality affects post-thaw plasma membrane intactness and sperm velocities in spermatozoa from Thai AI swamp buffaloes (Bubalus bubalis)

Altogether 218 frozen semen AI doses, prepared between 1980 and 1989 and also between 2003 and 2005 from 18 AI Thai swamp buffalo sires, were examined to determine whether seasonality affects post-thaw viability, as plasma membrane integrity (PMI, using SYBR-14/PI), plasma membrane stability (PMS, using Annexin-V/PI), or motility (Mot, using CASA). A thermoresistance test (38 degrees C for 60 min) was used to further analyze sperm survivability in vitro. All variables were compared over 3 seasons of the year (rainy: July-October; winter: November-February; and summer: March-June), with distinct ambient temperature and humidity. PMI (% of alive spermatozoa) was higher in winter (54.6%, P<0.001) than in the rainy (43.5%) or summer (46.7%) seasons. Outcomes of PMS (Annexin-V/PI assay) confirmed those of PMI, the highest PMS in spermatozoa processed in winter (55.7%, P<0.001). Spermatozoa depicting linear Mot post-thaw ranged from 48.2% to 48.8% across seasons (ns), proportions that decreased during incubation (33.5-37.9%), albeit without seasonal differences. The mean percentages of straight linear velocity (VSL), average path velocity (VAP), or curvilinear velocity (VCL) were higher (P<0.05-0.001) in the rainy season than in winter or summer, while average lateral head displacement (ALH) was higher (P<0.05) in summer, differences maintained after incubation. In conclusion, post-thaw PMS and PMI, assessed by flow cytometry, were significantly better in sperm samples processed during winter than in samples processed during the other seasons of the year, a seasonal difference not picked up by CASA, probably due to the larger number of spermatozoa assessed.

Liquid storage of Asian elephant (Elephas maximus) sperm at 4 °C

The Asian elephant (Elephas maximus) population in the wild has been in decline for several decades and breeding in captivity has not been self-sustaining. The use of artificial insemination (AI) can help overcome many of the difficulties associated with breeding elephants in captivity; however, the ability to store semen for extended periods of time is critical to the successful application of AI to elephants. The objective of the present study was to assess the effects of four different semen extenders and the presence of egg yolk on the viability and motility of Asian elephant semen stored at 4 degrees C. High quality ejaculates (n=4) were collected from two Asian elephant bulls by rectal massage. Aliquots of each ejaculate were extended in four different diluents (Beltsville thawing solution (BTS); Tris-citric acid (TCA)/fructose-based; Beltsville F5 (BF5); dextrose-supplemented phosphate-buffered saline (PBS)) with or without egg yolk then cooled and stored at 4 degrees C. The percentages of viable (viability) and motile (motility) sperm were evaluated at 8, 24 and 48 h following collection. The addition of egg yolk significantly reduced the percentage loss in viability from initial collection to 48 h compared to extenders without egg yolk (17.0 +/- 8.2 versus 32.6 +/- 8.9 decline in percent viable sperm in the population, respectively; P<0.05). Extender and egg yolk affected (P<0.005) total motility and percent progressively motile sperm at all evaluation times during incubation. TCA + egg yolk maintained higher (P<0.05) levels of progressive motility compared to other extenders supplemented with egg yolk. These results indicate that Asian elephant semen extended in TCA diluent supplemented with egg yolk can maintain at least 50% viability and motility when stored at 4 degrees C for 48 h.

Sperm cryopreservation in three species of endangered gazelles (Gazella cuvieri, G. dama mhorr, and G. dorcas neglecta)

Long-term storage of semen by cryopreservation, with high recovery rates on thawing, is essential for the establishment of genetic resource banks of endangered species. The purpose of the present study was to evaluate various diluents for the cryopreservation of spermatozoa from three species of gazelles (genus Gazella) in a captive breeding program. The diluents compared were Tes (N-tris(hydroxymethyl)methyl-2 aminoethane sulfonic acid)-Tris with 5% egg yolk and 6% glycerol (TEST) and Triladyl, yolk-citrate, Tris-trehalose, and Tris-lactose-all of them with 20% egg yolk and 6% (Triladyl) or 8% glycerol. Semen was obtained by electroejaculation from 12 G. cuvieri, 12 G. dama, and 13 G. dorcas males. Samples with less than 50% motile sperm, positive endosmosis, or acrosome integrity were not used. Diluted samples were loaded into 0.25-ml straws, cooled slowly to 5 degrees C over 1.5 h (-0.16 degrees C/min), equilibrated at that temperature for 2 h, frozen in nitrogen vapors for 10 min, and plunged into liquid nitrogen. Subsamples were assessed fresh, after refrigeration-equilibration, after freezing and thawing, and 2 h after thawing. Differences were seen between diluents, with best overall recovery rates after freezing and thawing found with Triladyl, TEST, and Tris-trehalose in G. cuvieri, TEST in G. dama, and Triladyl and TEST in G. dorcas. Differences were observed between species in the ability to withstand freezing and thawing, with best results seen in G. dorcas, intermediate results in G. dama, and worst results in G. cuvieri. These differences were inversely related to the average values of inbreeding of these populations. The underlying mechanism responsible for these differences may be a differential resistance to osmotic shock.