Offspring resulting from transfer of cryopreserved embryos in camel (Camelus dromedarius)

Successful vitrification of dromedary camel embryos using a novel embryo vitrification kit

Embryos (n = 87) collected 8 days after mating and 7 days after ovulation were vitrified using a camel-specific vitrification kit. Vitrification solutions (VS) containing 20% foetal calf serum, with or without 2% bovine serum albumin (BSA) were used to cryopreserve embryos, in three steps VS1 (5 min), VS2 (5 min) and VS3 (30-35 s) at room temperature (RT) before being loaded into open pulled straws and immediately frozen in liquid nitrogen. Embryos were subsequently thawed in warming solutions (WS) in three steps: WS1 at 37 °C (1 min), WS2 at RT (5 min) then into holding media at RT (5-60 min) prior to transfer, in pairs, into recipient camels 6 days after ovulation. There were 42 of 43 embryos viable after vitrification in media without BSA and these were subsequently transferred into 21 recipient females which resulted in ten pregnancies 60 days after transfer (48% pregnancy rate). There were 38 of 44 viable embryos vitrified in media containing BSA that were transferred in pairs into 19 recipient females which resulted in five pregnancies 60 days after transfer (26% pregnancy rate; P > 0.05). Of the total 15 foetuses that developed to 60 days of gestation after vitrification, 11 resulted from embryos of 200-499 μm diameter and four from embryos of 500-700 μm diameter (P > 0.05). There were encouraging results with use of this novel vitrification kit for the commercial application of cryopreservation of camel embryos with a diameter of 300-550 μm.

Preservation of dromedary camel embryos at 4 °C for up to 5 days: Factors affecting the pregnancy and pregnancy loss rates

The aims of the present study were to evaluate the effect of cooling of the dromedary camel embryos on the pregnancy and pregnancy loss rates, and to investigate the factors which might affect the outcomes of the transfer of cooled embryos. After the donors (n = 56) had been super-ovulated and mated, they were flushed at Day 8 or 9 post-mating. Of 487 collected embryos, 110 were refrigerated at 4°C for up to 5 days in holding medium (HM), flushing medium supplemented with 10% fetal calf serum (FM + FCS) or TCM199 supplemented with 50% FCS and HEPES (TCM + FCS + HEPES). Both fresh (n = 377) and cooled embryos were transferred individually into synchronized recipients. Pregnancy diagnoses were carried out at Days 18-19, 30 and 60 post-mating of the donors. Transferring of fresh embryos into the recipients resulted in significantly higher pregnancy rates at Days 18-19 (53.1% vs. 38.2%, P < 0.01), Day 30 (46.4% vs. 31.8%, P < 0.01) and Day 60 (42.4% vs. 26.4%, P < 0.005) compared with those of cooled embryos, respectively. Pregnancy rates after transferring cooled embryos progressively decreased with the prolongation of the storage period. A significant difference in the pregnancy rate (56% vs. 13%, respectively, P < 0.05) was recorded only at Days 18-19 between cooled embryos held for one day and those held for 5 days. The pregnancy rates at Days 18-19, Day 30 and Day 60 were non-significantly higher when TCM + HEPES and FCS medium used for cooling of embryos compared to those of FM + FCS or HM medium. Cooling of spherical embryos resulted in significantly higher pregnancy rates at Days 30 (45.6% vs. 17.0%, respectively, P < 0.005) and 60 (42.1 vs. 9.4%, respectively, P < 0.005) and a significantly lower pregnancy loss rate (11.1% vs. 66.6%, respectively, P < 0.005) compared to those resulting from cooling of folded embryos. Neither the size of embryo nor the day of flushing had a significant effect on the pregnancy and pregnancy loss rates after the transfer of cooled embryos. In conclusion, pregnancy could be obtained after the transfer of camel embryos refrigerated for up to 5 days. In addition, higher pregnancy rates could be obtained if only spherical embryos are selected for cooling.

Survival, re-expansion, and pregnancy outcome following vitrification of dromedary camel cloned blastocysts: A possible role of vitrification in improving clone pregnancy rate by weeding out poor competent embryos

There is a clinical demand for efficient cryopreservation of cloned camel embryos with considerable logistic and economic advantage. Vitrification of in vivo derived embryos has been reported in camels, but there is no study on vitrification of cloned embryos. Moreover, whether characteristic differences between cloned and in vivo derived embryos imply different vitrification requirement is unresolved. Here, we compared survival, re-expansion and pregnancy rates of cloned embryos vitrified using two commercial vitrification kits (Cryotec and Kitazato), developed basically for human embryos, and a vitrification protocol developed for in vivo camel embryos (CVP). Cloned embryos responded dynamically to vitrification-warming steps in commercial kits, with a flat shrinkage in the final vitrification solution and a quick re-expansion to the original volume immediately after transferring to the isotonic warming solution. Contrarily, full shrinkage was not observed in CVP method, and majority of embryos were still collapsed post-warming. The immediate re-expansion was highly associated and predictive of higher survival and total cell number, and also better redox state of embryos vitrified by Cryotec and Kitazato kits compared to CVP method. Importantly, while 30% blastomere loss, verified by differential dye exclusion test, was tolerated in vitrified embryos, >50% blastomeres loss in non-expanded blastocysts implied the minimal essential cell survival rate for blastocoelic cavity re-expansion in vitrified cloned camel blastocysts, irrespective of vitrification method. A protocol-based exposure of embryos to cryoprotectants indicated that cryoprotectant toxicity, per se, may not be involved in lower cryosurvival of embryos in CVP vs. Cryotec and Kitazato. The initial pregnancy rates were numerically higher in Cryotec and Kitazato frozen transfers compared to fresh transfer (56.3, 60 and 33.3%, respectively), and importantly, a higher percentage of established pregnancies in vitrified groups passed the critical 3 months period of early embryonic loss compared to sibling fresh clone pregnancies (50, 40, and 10%, respectively). Results confirmed the suitability of Cryotec and Kitazato kits for vitrification of cloned camel embryos and that vitrification may improve pregnancy outcome by weeding out poor competent embryos.

The use of some assisted reproductive technologies in old world camelids

The use of camels for racing, milking and as show animals is growing in popularity, thus there is increased enthusiasm to breed more of the genetically superior animals. This review highlights recent developments in assisted reproductive techniques in camels, such as embryo transfer and artificial insemination, to ensure more rapid genetic progress. This paper discusses the difficulties involved in handling the semen due to its high viscosity and ways to reduce it. It also examines methods for short term liquid storage of fresh semen with and without the use of antioxidants to reduce oxidative stress. The widespread use of AI in camels is hindered by the lack of a reliable method for deep freezing and long term storage but various freezing protocols, cryoprotectants and freezing and thawing methods are discussed as well as different insemination techniques. Embryo transfer requires the donor to be superovulated and the recipients synchronized. This review discusses different protocols used for superovulation of donor animals and the problems involved. It also examines various methods to synchronize recipients, or how to make best use of non-synchronized or non ovulated recipients. Cryopreservation of embryos would greatly improve the wider use of ET and spread of genetics worldwide so methods for slow cooling and new methods of vitrification with promising results are discussed.

Current status and future direction of cryopreservation of camelid embryos

Over the past 3 decades, and similar to the horse industry, fresh embryo transfer has been widely practiced on large commercial scales in different camelid species, especially the dromedary camel and alpaca. However, the inability to cryopreserve embryos significantly reduces its broader application, and as such limits the capacity to utilize elite genetic resources internationally. In addition, cryopreservation of the semen of camelids is also difficult, suggesting an extreme sensitivity of the germplasm to cooling and freezing. As a result, genetic resources of camelids must continue to be maintained as living collections of animals. Due to concerns over disease outbreaks such as that of the highly pathogenic Middle East Respiratory Syndrome in the Middle East and Asia, there is an urgent need to establish an effective gene banking system for camelid species, especially the camel. The current review compares and summarizes recent progress in the field of camelid embryo cryopreservation, identifying four possible reasons for the slow development of an effective protocol and describing eight future directions to improve the current protocols. At the same time, the results of a recent dromedary camel embryo transfer study which produced a high morphologic integrity and survival rate of Open Pulled Straw-vitrified embryos are also discussed.

Optimization of a vitrification protocol for hatched blastocysts from the dromedary camel (Camelus dromedarius)

The objective of this study was to modify and optimize a vitrification protocol (open pulled straw) that was originally designed for human oocytes and embryos, to make it suitable for the cryopreservation of camel hatched blastocysts. The original open pulled straw protocol was a complex process with 15-minute exposure of oocytes/embryos in 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (Me2SO) for equilibration, and cooling in 16% EG + 16% Me2SO + 1 M sucrose. Recognizing a need to better control the cryoprotectant (CPA) concentrations, while avoiding toxicity to the embryos, the effects on the survival rate and developmental potential of camel embryos in vitro were investigated using two different methods of loading the CPAs into the embryos (stepwise and semicontinuous increase in concentration), two different loading temperature/time (room temperature ∼24 °C/15 min and body 37 °C/3 min), and the replacement of Me2SO with EG alone or in combination with glycerol (Gly). A total of 145 in vivo-derived embryos were subjected to these processes, and after warming their morphological quality and integrity, and re-expansion was assessed after 0, 2, 24, 48, 72, and 96 hours of culture. Exposure of embryos in a stepwise method was more beneficial to the survival of embryos than was the semicontinuous process, and loading of CPAs at 37 °C with a short exposure time (3 minutes) resulted in an outcome comparable to the original processing at room temperature with a longer exposure time (15 minutes). The replacement of the Me2SO + EG mixture with EG only or a combination of EG + Gly in the vitrification medium significantly improved the outcome of all these evaluation criteria (P < 0.05). The modified protocol of loading EG at 37 °C for 3 minutes has increased the embryo survival of the original protocol from 67% to 91% and the developmental rate from 57% to 83% at 5-day culture. These results were comparable to or better than those reported in human or other species, indicating that this optimized method is well suited to any commercial embryo transfer program in the dromedary camel.

Preservation of caprine preantral follicle viability after cryopreservation in sucrose and ethylene glycol

Caprine preantral follicles within ovarian fragments were cryopreserved in the absence or presence of 0.5 M sucrose with or without 1 M dimethyl sulfoxide and/or 1 M ethylene glycol (EG). After being thawed, they were washed in minimum essential medium with or without 0.3 M sucrose. Histological analysis of follicle integrity immediately after cryopreservation showed consistent beneficial effects of including sucrose in the three cryoprotectant solutions analyzed when tissue was thawed without sucrose (53.9+/-14.8-82.4+/-3.2% normal vs 27.6+/-1.6-36.6+/-6.5%, P<0.05). However, in further studies, the addition of sucrose to the thaw solutions proved detrimental or of no benefit. An analysis of the cryopreserved material with calcein-AM and ethidium homodimer (markers for living and dead cells, respectively) gave comparable results to those obtained by histology. Follicles cryopreserved in EG, EG plus sucrose, or sucrose alone were cultured in vitro for 24 h following warming. During this culture period, viability fell most rapidly in material cryopreserved in sucrose alone and was no longer correlated with either the viability or integrity estimates made immediately after warming. By contrast, the viability of follicles cryopreserved in EG with sucrose and then cultured for 24 h was not significantly different from the cultured non-frozen controls. These results indicate that cryopreservation in 1 M EG plus 0.5 M sucrose combined with thawing without sucrose is effective for caprine ovarian tissue.

Effect of season and gonadotropins on the superovulatory response in camel (Camelus dromedarius)

The purpose of the present investigation was to study the extent to which season and the gonadotropin preparation interferes with the superovulatory response in the dromedary. Adult camels were treated for superovulation during the breeding (November to April) and non-breeding season (May to October). Animals were synchronized by daily i.m. injections of progesterone (125 mg/animal/day, Jurox, UK) for 10 to 14 days. Superovulation was induced by 400mg pFSH alone (Follitropin V, Vetrepharm, Canada) administered in eight descending doses at 12h intervals or a combination of PMSG (2000IU, Folligon, Intervet, The Netherlands), injected with last injection of progesterone and 400mg pFSH in eight descending doses. The follicular development was daily assessed by ultrasonography of the ovaries. The donors were classified as per their response to the superovulatory treatment into very good (>10 follicles), good (5-10 follicle), poor (2-4 follicles) or no response (1 or no follicle) on each ovary. Ovulation was induced by injecting 3000 IU hCG (Chorulon, Intervet) at the time of first mating. The donors were mated twice at an interval of 12h when all or most of the follicles reached to a size of about 1.0-1.7 cm. Camels were flushed non-surgically on Day 6 or 7 after the ovulation. The proportion of camels showing very good response during the breeding as well as non-breeding season was higher (P<0.05) when a combination of pFSH and eCG was used compared with pFSH only. There was no difference (P>0.05) in the proportion of donors flushed successfully (embryos recovered) when treated either with a combination of pFSH and eCG or pFSH alone during the breeding and non-breeding season. The rate of recovery of ova/embryos and proportion of transferable embryos was higher (P<0.05) when donors were treated with pFSH+eCG compared with pFSH only during the breeding as well as non-breeding season. The results may indicate that ova/embryo recovery rate of the dromedary is influenced by the gonadotropin preparation but is not appreciably affected by the season.