Effect of Disaccharide Inclusion in Vitrification and Warming Solutions on Developmental Competence of Vitrified/Warmed Germinal Vesicle Stage Buffalo Oocytes

BACKGROUND

Cryopreservation of immature oocyte is a potential strategy for preserving the female germline, providing a non-seasonal, easily accessible source for reproduction and science. Exposure of oocytes to high concentrations of cryoprotectants during vitrification is toxic and can negatively impact the fertilization ability and development of vitrified/warmed oocytes.

OBJECTIVE

1) to evaluate the effects of exposure of buffalo germinal vesicle (GV) oocytes to different vitrification solutions (VS), either supplemented with or without sucrose, on cumulus expansion and nuclear maturation following IVM; and 2) to compare the effects of sucrose and trehalose in the warming solution on developmental competence of buffalo oocytes vitrified at the GV-stage.

MATERIALS AND METHODS

Cumulus oocyte complexes (COCs) obtained at slaughter from mature buffalo ovaries were randomly assigned into five groups: control - directly subjected to IVM); VS1 group - exposed to 20% ethylene glycol (EG) + 20% glycerol (GLY) + 0.5 M sucrose; VS2 group - exposed to 20% EG + 20% GLY; VS3 group - subjected to 20% EG+20% dimethyl sulfoxide (DMSO) + 0.5 M sucrose; and VS4 group - subjected to 20% EG+20% DMSO. Following cryoprotectant dilution, viable oocytes were matured in vitro for 22 h; cumulus expansion and nuclear maturation were then evaluated (Experiment 1). COCs were vitrified by solid surface vitrification (SSV) in a solution composed of 20% EG + 20% DMSO (VS4). Following vitrification, COCs were warmed in a solution composed of either sucrose or trehalose in decreasing concentrations (1 M, 0.5 M and 0.25 M). Morphologically viable oocytes were matured, fertilized and cultured in vitro. Cleavage and blastocyst rates were evaluated at 30 h and day 7 post-insemination (p.i.), respectively (Experiment 2).

RESULTS

Exposure of GV-buffalo oocytes to different cryoprotectant combinations did not significantly affect cumulus expansion following IVM. However, nuclear maturation rate (oocytes at MII) was significantly higher (P<0.05) in the groups exposed to sucrose-free vitrification solutions (VS2 and VS4) and not significantly different from the control. Compared with the control group, the cleavage and blastocyst rates were significantly (P<0.05) lower in oocytes vitrified and then warmed in a solution containing trehalose; whilst this was not the case when sucrose was present in the solution.

CONCLUSION

Our results suggest that exposure of buffalo GV-oocytes to sucrose-free vitrification solutions improved nuclear maturation after IVM. Moreover, warming of vitrified buffalo oocytes in sucrose-based solution improved preimplantation development following IVM and IVF compared to trehalose based media.

198 Comparison of invitro production of bison and cattle embryos and effect of L-carnitine during maturation of bison oocytes

Bison are an important species in North America, both economically and culturally. Although assisted reproductive technologies have been applied to preserve the genetic diversity of bison, development of these technologies remains limited for this species. The objective of the present study was to compare success rates of oocyte maturation, fertilization, and embryo development invitro in bison versus cattle (experiment 1). Cumulus-oocyte complexes obtained from abattoir-derived cattle and bison ovaries were matured, fertilized with frozen semen, and cultured invitro using standard procedures (De La Torre-Sanchez et al. 2006 Reprod. Fertil. Dev. 18, 585-596). At least three replicates were repeated for each experimental group. Oocyte recovery rate was lower in bison than in cattle (4.3; 2797/699 vs. 6.7; 4138/677, oocyte/ovary; P&lt;0.01, t-test). Nuclear maturation (oocytes at MII, 23h post-IVM) and fertilization rates (oocytes with 2 pronuclei 18h post-insemination; p.i.) evaluated by Hoechst stain were lower (P&lt;0.01, chi-square) for bison (65.1%; 56/86 and 32.7%; 18/55, respectively) than for cattle (88.3%; 83/94 and 70.9%; 39/55, respectively). Polyspermy tended to be higher in bison than in cattle (12.7% vs. 3.6%, P=0.08). The percentages of 2-cell embryos tended to be lower in bison than in cattle (13.5% vs. 25.0%, P&gt;0.05) at 24h p.i. but by 30h p.i., this difference increased (33.7% vs. 67.0%, P&lt;0.01, chi-square). Cleavage (Day 3) and blastocyst (Day 7) rates were lower (P&lt;0.01, chi-square) for bison (58.2%; 280/481 and 14.6%; 70/481, respectively) than for cattle (90.8%; 405/446 and 22.9%; 102/446, respectively). Total cell number (74.9±4.8 vs.114.2±5.8), trophectoderm cell numbers (57.9±4.6 vs. 89.2±4.8) and inner cell mass cell numbers (16.9±2.3 vs. 25±1.9) as determined by Hoechst and propidium iodide were all lower (P&lt;0.01, t-test) in bison than in cattle blastocysts. To improve oocyte competence in bison, we evaluated effects of L-carnitine (LC) supplementation during IVM on developmental potential of bison oocytes (experiment 2). Cumulus-oocyte complexes were matured in IVM medium supplemented with 0, 0.15, 0.3, 0.6, or 1.2mgmL−1 LC. No differences were observed in cleavage rates of control (0mgmL−1 LC) and LC-treated groups (values ranged from 60.0 to 66.4%). Interestingly, a dose-dependent increase in blastocyst development was found with the lowest value recorded in control group (10.4%; 14/134) and the highest value in the 1.2mgmL−1 LC supplemented group (22.2%; 23/105; P&lt;0.01, chi-square, n=4). Adding 1.2mgmL−1 LC to the IVM medium improved the percentage of hatching blastocysts compared with the control. In conclusion, bison oocytes exhibited lower invitro maturation, fertilization, and developmental rates compared with cattle oocytes using our system, and bison embryos were delayed in the timing of first cleavage. L-Carnitine supplementation during IVM of bison oocytes improved the preimplantation development and quality of invitro-produced blastocysts.

Optimization of the Protocol for Cryopreservation of Arabian Stallion Spermatozoa: Effects of Centrifugation, Semen Extenders and Cryoprotectants

BACKGROUND

Cryopreservation of Arabian stallion semen is important in order to improve the function and fertility of frozen/thawed semen in this breed.

OBJECTIVE

To investigate the effects of centrifugation, type of semen extenders, and type of cryoprotectants on the quality of frozen/thawed Arabian stallion spermatozoa.

MATERIALS AND METHODS

Semen samples collected from four adult Arabian stallions (one ejaculate per week for 10 consecutive weeks) were either processed directly without centrifugation (no centrifugation; NC) or subjected to centrifugation on the gel-free fraction. Centrifugation protocols were divided into six categories; 600 x g for 10 min (C1), 600 x g for 15 min (C2), 900 x g for 10 min (C3), 900 x g for 15 min (C4), 1200 x g for 10 min (C5), or 1200 x g for 15 min (C6) (Experiment 1). Two semen extenders, INRA-82 and modified Kenney's were compared (Experiment 2). Three different cryoprotectants, [namely 5% glycerol, 5% dimethylformamide (DMF) and 2.5% glycerol] plus 2.5% DMF were used (Experiment 3). Following freezing and thawing, motility, viability, plasma membrane integrity, acrosome status and viability index were evaluated.

RESULTS

Centrifugation at 600 x g for 15 min before cryopreservation increased (P< 0.05) sperm motility, viability, membrane integrity and percentage of spermatozoa with intact acrosome compared to other centrifugation protocols. Dilution of Arabian stallion semen with INRA-82 before cryopreservation improved (P< 0.05) sperm quality after freezing and thawing compared to modified Kenney's extender. Supplementation of semen diluent INRA-82 with 5% DMF improved (P< 0.05) the quality of frozen/thawed Arabian stallion spermatozoa compared to 5% glycerol.

CONCLUSION

These findings suggest that optimized conditions such as centrifugation, types of semen extenders and cryoprotectants play an important role in processing Arabian stallion spermatozoa for cryopreservation.

49 Developmental Potential of Dromedary Camel Oocytes Vitrified at the Germinal Vesicle Stage: Effects of Different Cryoprotectant Combinations and Cryo-Carriers

Cryopreservation of oocyte would be an alternative to overcome the limited availability of dromedary camel oocytes and allow improvements in in vitro production in this species. Our aim was to develop a protocol for vitrification of dromedary camel oocytes at the germinal vesicle (GV) stage using various cryoprotectant combinations and cryo-carriers. In experiment 1, cumulus–ppcyte complexes (COC) obtained at slaughter were equilibrated in a solution composed of 10% ethylene glycol (EG) and 0.25 M trehalose. The oocytes were then exposed for 60 s to vitrification solutions (VS) composed of 20% EG and 20% dimethyl sulfoxide (DMSO; VS1) or 25% EG plus 25% DMSO (VS2) or 25% EG and 25% glycerol (VS3). The COC were then transferred into decreasing concentration of trehalose solution (toxicity test). In experiment 2, COC were randomly divided into 4 groups and vitrified by using straw or open pulled-straw (OPS) or solid surface vitrification (SSV) or cryotop in VS1 or VS2. Following vitrification and warming viable oocytes were matured in vitro for 30 h at 39°C in 5% CO2 in air. Matured oocytes were fertilized in vitro by epididymal spermatozoa of mature male camels and then cultured in modified KSOMaa medium for 7 days. Oocyte viability, maturation, fertilization, and embryo development were evaluated. Data were analysed using one-way ANOVA and t-test. Viability and nuclear maturation rates were significantly lower (P ≤ 0.05) in oocytes exposed to VS3 (44.8% and 34.0%) than those exposed to VS1 (68.2% and 48.0%) and VS2 (79.3% and 56.9%). Although recovery rates were significantly lower (P ≤ 0.05) in oocytes vitrified using SSV or cryotop in either VS1 or VS2 solutions (66.9% to 71.1%) than those vitrified by straws using VS1 or VS2 solutions (86.3% to 91.0%), survival rates were higher in SSV and cryotop groups (90.7% to 94.8%) than straw and OPS (68.2% to 86.5%) groups. Among vitrified groups, maturation and fertilization rates (51.8% and 39.2%, respectively) were the highest in the cryotop-VS2 group. Those values were comparable to those seen in the controls (59.2% and 44.6%, respectively). Cleavage (22.5% to 27.9%), morula (13.2% to 14.5%), and blastocyst (6.4% to 8.5%) rates were significantly higher (P ≤ 0.05) in SSV and cryotop groups than in straws. No significant differences were observed in these parameters between cryotop and control groups. Together, the results show that both vitrification solution and cryodevice affect viability and developmental competence of vitrified/warmed dromedary camel oocytes. We report for the first time that dromedary camel oocytes vitrified at the GV stage have the ability to be matured, fertilized, and subsequently develop in vitro to produce blastocyst embryos at frequencies comparable to those obtained using fresh oocytes.

127 L-Carnitine Supplementation During In Vitro Maturation Improves Developmental Competence of Canine Oocytes

In vitro embryo production (IVP) in the domestic bitch is important for conservation of endangered canids. Compared with various domestic animals, the development of assisted reproductive technologies (ART) in the dog has lagged behind, mainly due to the low percentage of oocytes that can reach metaphase II (MII) stage after in vitro maturation (IVM). Beneficial effects of l-carnitine (LC) on embryonic development in culture have been reported in many mammalian species; however, no studies have been conducted in dogs. The aim of the present study was to investigate the effect of LC supplementation during IVM of canine oocytes on nuclear maturation, fertilization status, and pre-implantation development following IVM/IVF. Cumulus-oocyte complexes (COC) were collected by slicing ovaries obtained from dogs (n = 20, 1 to 6 years of age) after ovariohysterectomy. The COC were subjected to IVM for 72 h in a medium (TCM-199) supplemented with LC at different concentrations (0.1, 0.3, 0.6, 1.0, or 2.0 mg mL−1) or without LC supplements (0 mg mL−1; control). Matured oocytes were fertilized in vitro with frozen–thawed spermatozoa, and presumptive zygotes were cultured in SOF medium for 7 days. Frequencies of nuclear maturation (72 h post-IVM), fertilization rates (18 h post-insemination), and embryo development (Days 2 to 5 post-insemination) were evaluated. Data were analysed by one-way ANOVA followed by Tukey’s multiple comparisons test. Supplementation of IVM medium with 0.3 or 0.6 mg mL−1 LC significantly improved (P ≤ 0.05) maturation (35.4% and 41.4%) and fertilization (21.3% and 25.8%) rates compared with the controls and with other LC-supplemented groups; values ranged from 20.1% to 25.0% for maturation and from 12.1% to 14.6% for fertilization. Cleavage (2- to 16-cell stages) was significantly higher (P ≤ 0.05) in the 0.6 mg mL−1 LC supplemented group than the 0.3 mg mL−1 supplemented group (16.3% v. 13.3%). These values were significantly higher (P ≤ 0.05) than those in other groups. Interestingly, 4.5% of IVM/IVF oocytes were developed to morula in 0.6 mg mL−1 LC supplemented group which was significantly higher (P ≤ 0.05) than those developed in the 0.3 mg mL−1 supplemented group (1.0%). No embryos developed beyond the 2- to 16-cell stage in the rest of the groups. In conclusion, l-carnitine supplementation during IVM is particularly efficient in improving nuclear maturation and pre-implantation embryo development of canine oocytes after IVF. These outcomes are important for the improvement of IVM conditions that can advance the efficiency of ART in dogs.

41 DEVELOPMENTAL POTENTIAL OF BUFFALO OOCYTES VITRIFIED AT THE GERMINAL VESICLE STAGE: EFFECTS OF DIFFERENT CRYOPROTECTANT COMBINATIONS AND CRYODEVICES

The cryopreservation of immature oocytes would generate a readily available, nonseasonal source of female gametes for both research and reproduction. In domestic animals, the most promising results in the field of oocyte cryopreservation have been reported in cattle, and a few experiments have been conducted on buffalo. The aim of the present study was to compare the effects of different cryoprotectant combinations and different cryodevices on viability and subsequent development of buffalo oocytes vitrified at the germinal vesicle stage. Cumulus-oocyte complexes obtained at slaughter from mature buffalos were vitrified by using either straw or open pulled-straw or solid surface vitrification (SSV) in a solution composed of either 20% ethylene glycol (EG) + 20% glycerol or 20% EG + 20% dimethylsulfoxide (DMSO). Following vitrification and warming, viable oocytes were matured in vitro for 22 h. Matured oocytes were either evaluated for nuclear maturation or fertilized and cultured in vitro for 7 days. Recovery rate was significantly higher (P < 0.05) in the oocytes vitrified by straw in 20% EG + 20% glycerol (92.6%) as compared with the other groups. Percentages of viable oocytes were significantly higher (P < 0.05) in the oocytes vitrified in 20% EG + 20% DMSO using SSV (95.7%) than those in the other groups (from 80 to 88.0%). Among the vitrified groups, the highest maturation rate was achieved in SSV with 20% EG + 20% DMSO group (56.7%). This value was comparable with those in the control group (62.1%). After IVF and embryo culture, the highest cleavage and blastocyst rates were obtained in SSV with 20% EG + 20% DMSO group (35.7 and 21.4%, respectively), and these values were nearly similar to those in the control group (38.7 and 25.8%, respectively). Vitrification of oocytes by straw or open pulled-straw resulted in significantly lower (P < 0.05) blastocyst rates (2.6 and 11.5%) as compared with the control. In conclusion, buffalo oocytes vitrified at the germinal vesicle stage can be matured, fertilized, and developed in vitro and produce high frequencies of blastocyst embryos. Solid surface vitrification may be superior to straw and open pulled-straw in vitrification of immature buffalo oocytes because this technique results in higher survival and embryo development rates.

Effect of Cytochalasin B pretreatment on developmental potential of ovine oocytes vitrified at the germinal vesicle stage

Oocyte cryopreservation remains a challenge in most mammalian species because of their sensitivities to chilling injuries. Relaxation of the cytoskeleton during vitrification may improve post-thaw viability and pre-implantation embryo development. The aim of this study was to investigate the effect of cytochalasin B (CB) pre-treatment before vitrification on viability, frequencies of in vitro fertilisation (IVF) and subsequent development of ovine cumulus-oocyte complexes (COCs) vitrified at the germinal vesicle (GV) stage using cryoloop. COCs obtained at slaughter were randomly divided into two groups and incubated with or without 7.5µg/mL CB for 60 min. Oocytes from each group were then vitrified using a cryoloop or used as toxicity and controls. Oocytes were then matured, fertilised, and cultured in vitro for 7 days. Viability following vitrifiaction and warming, fertilisation events following IVF and subsequent pre-implantation embryo development were evaluated. No significant differences were observed in survival rates between CB treated and non-treated oocytes in both vitrified and toxicity groups. Frequencies of fertilisation were increased in CB-vitrified group (oocytes pre-treated with CB before vitrification) than those vitrified without CB pre-treatment (57.0% vs 40.7%). Cleavage was significantly lower (P < 0.05) in vitrified and CB-vitrified oocytes at both 24 hpi (12.5% vs 9.1%) and 48 hpi (25.0% vs 16.2%) than in other groups. Based on the numbers of cleaved oocytes, (48 hpi), 16.1% and 18.8% of the cleaved embryos developed to blastocysts in both vitrified and CB-vitrified groups. These values did not differ significantly from those obtained in CB-control group (37.8%). No significant differences were observed in mean cell numbers per blastocyst between all groups. In conclusion, pre-treatment of ovine GV oocytes with cytochalasin B as cytoskeleton stabilizer before vitrification increased frequencies of in vitro fertilisation and subsequently resulted in production of good quality late stage pre-implantation embryos following IVF.

161 IN VITRO FERTILIZATION OF DROMEDARY CAMEL (CAMELUS DROMEDARIUS) OOCYTES WITH EPIDIDYMAL SPERMATOZOA

Various techniques such as AI and ET have been reported to improve reproductive efficiency and genetic potential in camelids. In vitro fertilization and the development of IVP embryos are considered an alternative for genetic improvement in this species. This study investigated the effects of different sperm cell concentrations (1, 2, 3 and 4 × 106 sperm mL–1), different capacitating materials (5 mM caffeine, 10 μg mL–1 of heparin, 10 mg mL–1 of theophylline, 1 mM calcium ionophore A23178 and 10 μg of heparin + 5 mM caffeine), post-slaughter epididymal flushing time and fertilization media supplements (Fert-TALP + 6 mg mL–1 of BSA and Fert-TALP + 3 mg mL–1 of polyvinylpyrrolidone ) on fertilization rates and subsequent development of dromedary camel oocytes. Cumulus–oocyte complexes obtained at slaughter were matured in vitro in TCM-199 for 36 h at 39°C in a humidified atmosphere of 5% CO2. For IVF, spermatozoa were collected from epididymides of slaughtered male camels at 1 to 2 h post-slaughter or after 24 h of epididymal storage at 4°C. The spermatozoa were then prepared for IVF by the swim-up technique. Following sperm capacitation, oocytes and spermatozoa were co-incubated for 18 h. Oocytes were then stained using aceto-orcein for evaluation of fertilization events. Presumptive zygotes were cultured in vitro in TCM-199 medium supplemented with 5% FCS for 9 days at 39°C in a humidified atmosphere of 5% O2, 5% CO2 and 90% N2. At least 3 replicates were performed for each experimental group. Data were analysed by chi-square test. Fertilization rates were 55.5, 62.5, 62.7 and 47.2% in oocytes inseminated with 1, 2, 3, or 4 × 106 sperm mL–1, respectively. Normal fertilization rate (oocytes with 2 pronuclei) was higher (P =  0.06) in oocytes inseminated with 2 × 106 sperm mL–1 (29.7%) than in those inseminated by 4 × 106 sperm mL–1 (11.1%). Treatment of epididymal spermatozoa with 5 mM caffeine significantly increased (P ≤ 0.05) fertilization rate (61.9%) compared with calcium ionophore A23178 (32.4%). These values were not significantly different from other groups (38.5, 54.1 and 50.0% in heparin, theophylline and heparin + caffeine, respectively). Normal fertilization was highest (25.4%) in oocytes inseminated with caffeine-treated spermatozoa. Insemination of oocytes in Fert-TALP medium containing BSA resulted in a higher fertilization rate (21.4%) compared with oocytes in polyvinylpyrrolidone-supplemented medium (5.7%; P =  0.06). Storage of camel epididymides at 4°C for 24 h did not affect fertilization rates. Cleavage rate (48 h post-insemination) was higher in oocytes fertilized with caffeine-treated spermatozoa than in oocytes in the theophylline group (26.8 vs 10.5%; P =  0.08). No significant difference was observed in the frequency of blastocyst development (5 days post-insemination) between the 2 groups (5.4 vs 2.6%); based on the number of cleaved oocytes, the same proportions of blastocyst embryos were reported (20.0 and 25.0%). Taken together, these results suggest that dromedary camel oocytes can be matured, fertilized and subsequently developed in vitro with high developmental potential. Epididymal spermatozoa at a concentration of 2 × 106 sperm mL–1 prepared in a medium containing caffeine as a capacitating agent can be used effectively in IVF of camel oocytes.

79 DEVELOPMENTAL COMPETENCE OF OVINE OOCYTES VITRIFIED AT GERMINAL VESICLE STAGE: IN VITRO FERTILIZATION, PARTHENOGENETIC ACTIVATION, AND SOMATIC CELL NUCLEAR TRANSFER

Oocyte cryopreservation represents an important development in the field of assisted reproductive technologies. This study investigated the effects of vitrification on spindle morphology following subsequent in vitro maturation (IVM), cleavage, and development following IVF and parthenogenetic activation. The developmental competence of ovine oocytes vitrified at the germinal vesicle (GV) stage, matured, and used as cytoplast recipients for somatic cell nuclear transfer (SCNT) was also determined. Cumulus–oocyte complexes obtained at slaughter were divided into 3 groups: 1) untreated (control), 2) toxicity (exposed to vitrification solutions without freezing), and 3) vitrified (2008 Reprod. Fertil. Dev. 20, 122). At 24 hpm (hours post onset of maturation), oocytes were subjected to 1) immunostaining, 2) IVF, or 3) activation by 2 different protocols [calcium ionophore, cycloheximide, and cytochalasin B (CA+CHX/CB), or strontium and CB (Sr/CB)]. The SCNT was performed as previously described (2010 Reprod. Fertil. Dev. 22, 1000–1014). Presumptive zygotes were cultured in vitro for 7 days. No significant differences (P > 0.05; chi-square) were observed in the frequencies of oocytes with normal spindle configuration between vitrified, toxicity, and control groups (50.0, 54.9, and 70.4%, respectively). Cleavage 24, 48 hpi, and morula development (5 days pi) were significantly decreased (P < 0.01) in the vitrified group (17.3, 42.9, and 36.4%) compared with toxicity (47.0, 85.3, and 60.7%) and control (68.9, 89.7, and 62.6%) groups. Blastocyst development significantly decreased (P < 0.01) in the vitrified group (12.3%) compared with toxicity (42.7%) and control (40.4%) groups. Based on cleaved embryos, no significant difference was observed between vitrified and control groups (29.4 v. 45.1%). Post-activation, cleavage 24 hpa (hours post-activation, 6.2 v. 3.8%) and 48 hpa (28.4 v. 27.5%) was significantly lower (P < 0.05) in vitrified oocytes activated by (CA+CHX/CB and Sr/CB) than other groups. No blastocyst developed from vitrified oocytes activated by CA+CHX/CB; however, 3.8% developed from Sr/CB oocytes. This was significantly (P < 0.05) lower than toxicity and control (20.0 and 27.3%) groups. Following SCNT, high frequencies of enucleation (99%) and fusion (98%) were achieved in vitrified and control groups. Cleavage 24 and 48 hpa significantly decreased (P < 0.05) in the vitrified group (31.0 and 48.0%) compared with the control (55.1 and 85.0%). No significant differences were observed in morula (38.0 v. 46.7%) and blastocyst (13.0 v. 23.4%) development. The proportion of cleaved embryos that developed to blastocyst stages was similar in both groups (27.0%). No significant differences (t-test) were observed in total cell numbers, apoptotic nuclei, and proportion of diploid embryos. In conclusion, ovine oocytes vitrified at GV stage can be matured, fertilized, and develop in vitro with high developmental potential. Strontium can be used effectively for activation of vitrified/thawed ovine oocytes. Vitrified/thawed ovine oocytes were used successfully for the first time as recipient cytoplasts for SCNT and produced high frequencies of good-quality blastocyst stage embryos.

102 EFFECT OF DEMECOLCINE PRE-TREATMENT ON VIABILITY, TIMING OF FIRST POLAR BODY EXTRUSION, SPINDLE CONFIGURATION, AND SUBSEQUENT DEVELOPMENT OF OVINE OOCYTES VITRIFIED AT GERMINAL VESICLE STAGE

Oocyte cryopreservation is a potentially valuable way of preserving female germ cells. However, to date the reported developmental competence of cryopreserved oocytes is low. The objectives of this study were to investigate the effects of demecolcine pretreatment on viability, timing of the first polar body extrusion (PBI), spindle, chromatin organization, and in vitro embryo development of ovine vitrified germinal vesicle (GV) oocytes after in vitro fertilization (IVF) and parthenogenetic activation. Cumulus-oocyte complexes (COC) aspirated from ovine ovaries collected at slaughter were selected and randomly divided into 3 groups: (1) untreated (in vitro matured, IVM) as a control, (2) vitrified (Moawad AR et al. 2009 Reprod. Fertil. Dev. 21, 135 abst), and (3) deme + vitrified (oocytes were incubated with 0.1 μg mL-1 demecolcine for 20 min before vitrification). After vitrification COC were thawed and matured in vitro for 24 h. Following IVM, oocytes from 3 groups were subsequently subjected to (1) immunostaining, (2) IVF, or (3) activation. Presumptive zygotes were cultured in vitro in SOF media for 7 days. Data were analyzed using chisquare and t-test. No significant differences (P > 0.05) were observed in survival rates between deme + vitrified (90.8%, 324/357) and vitrified (87.2%, 211/242). However, the numbers of oocytes with PBI in two vitrified groups at 18 h (20.4 and 8.5 v. 47.1%) and 24 h post IVM (51 and 43.2 v. 88.5%) were significantly lower (P < 0.01) than those in the control. Percentage of normal spindle and chromatin configuration in the two vitrified groups also significantly decreased (P < 0.05) compared with those in the control (42.5 and 41.8 v. 76.5%), whereas missing spindle in the 2 vitrified groups significantly increased (P < 0.001) compared with the controls (47.5 and 32.7 v. 3.9%). Following IVF (pi), cleavage rates at 24.48 hpi and morula development (5 days pi) were significantly lower (P < 0.001) in deme + vitrified (6.1, 43.1, and 28.5%) and vitrified groups (3.3, 30.1, and 22.9%) than control (50.4, 82.4, and 46.4%). Blastocyst development in deme + vitrified (9.8%) and control (33.6%) was significantly higher (P < 0.01) than in vitrified group (1.3%). Hatched blastocysts were observed only in deme + vitrified and control groups (4.9 v. 12.8%). In addition, post activation (pa) cleavage rates in deme + vitrified (10.3 v. 40.7%) and control (52.5 v. 76.7%) at 24 and 48 hpa were significantly higher (P < 0.05) than those in the vitrified group. Blastocyst development in deme + vitrified (4.8%) was higher than that in the vitrified group (1.8%), but not significant (P > 0.05); however, these values were still significantly lower (P < 0.001) than those in the control (24.2%). No significant differences were observed in total cell numbers per blastocyst between all the groups. Taken together, these results suggest that pretreatment of oocytes with demecolcine before vitrification could improve the developmental competence of ovine vitrified-thawed GV-stage oocytes. A. R. Moawad was supported by the Egyptian government.

70 VITRIFICATION OF IMMATURE OVINE OOCYTES WITH CRYOLOOP: EFFECT OF CYTOCHALASIN B PRETREATMENT ON SUBSEQUENT DEVELOPMENT

Oocyte cryopreservation is still a challenge in most mammalian species because of their extreme sensitivity to chilling injuries. Relaxation of the cytoskeleton during vitrification may improve post-thaw survival and subsequent development; however, a previous study in immature [germinal vesicle (GV) stage] oocytes from prepubertal lambs reported that pretreatment with cytochalasin B (CB) did not improve maturation (Silvestre MA et al. 2006 Anim. Reprod. Sci. 93, 176–182). We previously reported that GV oocytes from mature ewes can be vitrified using a cryoloop with high survival, maturation, and subsequent in vitro fertilization (Moawad AR and Campbell KHS 2008 Reprod. Fertil. Dev. 20, 122). The aim of this study was to evaluate the effects of CB pretreatment prior to vitrification of GV oocytes (from mature ewes) on subsequent development. Cumulus–oocyte complexes obtained at slaughter were randomly divided into 2 groups and incubated with or without 7.5 μg mL–1 CB for 60 min before vitrification. Oocytes from each group were vitrified or used as toxicity and controls. For vitrification, oocytes were equilibrated in 10% ethylene glycol (EG) and 0.25 m trehalose (T) in HEPES/TCM-199 plus 10% fetal bovine serum (BM) for 3 min. Oocytes were then exposed to vitrification solution (20% EG and 20% DMSO in BM), loaded into the cryoloop within 1 min, and immersed in liquid nitrogen. Oocytes were warmed by exposure to (1) 10% EG and 1 m T in BM, (2) 0.5 m T in BM, and (3) BM for 3 min in each solution at 39°C. Oocytes were then matured, fertilized, and cultured in vitro as previously described. The frequency of cleavage 24 and 48 h post-insemination (pi), development to morula (5 days pi), blastocyst (7 days pi), and total cell numbers of blastocyst-stage embryos were evaluated. Cleavage was significantly lower (P < 0.001) in vitrified and CB-vitrified groups at both 24 h pi (15.2 v. 14.7%) and 48 h pi (27.3 v. 23.5%) than in other groups. Development to morula stage was significantly lower (P < 0.001) in vitrified and CB-vitrified oocytes (12.1 v. 17.7%) than in toxicity, CB-control, and control groups (43.1, 42.6, and 52.8%, respectively); however, no significant difference (P > 0.05) was observed between CB-vitrified and CB-toxicity groups. There was a significant decrease (P < 0.01) in development to blastocyst in CB-vitrified (2.9%) compared with CB-control (22.9%) and control (24.5%), but this did not differ significantly (P > 0.05) from toxicity and CB-toxicity groups (9.8 v. 11.4%). No blastocysts developed from the vitrified group. Hatched blastocysts were observed only in CB-control and control groups (8.2 v. 5.7%). Total cell numbers were significantly greater (P < 0.05) in control blastocysts than in toxicity, CB-vitrified, and CB-control (143 v. 87.25, 73, and 82, respectively). However, this did not differ significantly from the CB-toxicity group (115). These results support our previous data and suggest that pretreatment of GV-stage ovine oocytes with CB prior to vitrification has a positive effect on subsequent development.

82 VITRIFICATION OF IMMATURE OVINE OOCYTES WITH CRYOLOOP™: EFFECT ON MEIOTIC MATURATION

Oocyte cryopreservation will become an important tool for the creation of genetic resources bank in domestic animals. Many problems have been described following cryopreservation of MII oocytes, including spindle disorganization (Ledda et al. 2007 Reprod. Fertil. Dev. 19, 13–23) and loss or clumping of microtubules resulting in some scattered chromosomes (Sathananthan et al. 1988 Hum. Reprod. 3, 968–977). Freezing of immature oocytes at the geminal vesicle stage might circumvent these problems because at this stage the genetic material is contained within the contours of a nuclear envelope (Siqeira-Pyles and Landim-Alvarenga 2005 Anim. Reprod. Sci. 193, 176–182). However, the number of reports relating to cryopreservation of immature oocytes remains low and it has been suggested that immature oocytes are more susceptible to cryoinjuries (Ledda et al. 2007). The aim of the present work was to study the effect of CryoLoop™ (Hampton Research, Aliso Viejo, CA, USA) vitrification on survival and subsequent meiotic maturation of immature ovine oocytes. Cumulus–oocyte complexes (COCs) were isolated from ovaries of slaughtered sheep. COCs were washed three times in basal medium [BM (HEPES–TCM-199 supplemented with 10% fetal bovine serum)], and then exposed to equilibration solution (10% ethylene glycol (EG) and 0.25 m trehalose (T) in BM for 3 min. After that, COCs were exposed to vitrification solution (20% EG and 20% DMSO in BM), loaded into the CryoLoop within 1 min, and immersed in liquid nitrogen. Following cryopreservation, COCs were warmed by exposure of oocytes to (1) 10% EG and 1 mT in BM, (2) 0.5 mT in BM, and (3) BM for 3 min in each solution at 39�C. Then oocytes were matured in vitro for 24 h in maturation medium, as previously described (Lee and Campbell 2006 Biol. Reprod. 74, 691–698). The nuclear maturation of oocytes was determined using aceto-orcein staining. Oocytes were classified into four stages: germinal vesicle (GV), metaphase-I (MI), anaphase-I + telophase-I (AI/TI), and metaphase-II (MII). Oocytes at MII stage were considered matured. Data were analyzed using chi-square test. The survival rate of oocytes after vitrification and warming based on oocyte morphology was 72.6% (61/84). Numbers of oocytes remaining at the GV stage were significantly higher in the vitrified group than in the control group (43.4 v. 12.6%, respectively; P < 0.01). Maturation to MII stage was higher (63.2%, 55/87) in the control group than in the vitrified group (43.4%, 23/53); however, the difference was not significant. Also, there were no significant differences between vitrified and control groups in terms of MI and AI/TI (7.5 and 5.7 v. 10.3 and 13.8%, respectively). In conclusion, immature ovine oocytes can be vitrified using CryoLoop with high survival and maturation rates.