In vitro culture of silver fox embryos

The Domestic Dog Embryo: In Vitro Fertilization, Culture, and Transfer

Advances in embryo technologies in the domestic dog have made significant strides in the past decade. This progress has been spurred by interests in taking advantage of the dog as a biomedical research model for human and companion animal medicine, developing assisted reproductive technologies to manage genetic diversity in endangered canids maintained ex situ, and improving breeding in rare or working breeds of dogs. Here, we focus on recent advancements and techniques for collection of in vivo-matured oocytes, in vitro fertilization (IVF), in vitro culture of early (≤8-cell) and advanced stage (≥16-cell) embryos, and embryo transfer.

Post-thaw viability of in vivo-produced canine blastocysts cryopreserved by slow freezing

The objectives were to evaluate the reexpansion blastocoele rate, post-thaw viability, and in vitro development of canine blastocysts cryopreserved by slow freezing in 1.0 m glycerol (GLY) or 1.5 m ethylene glycol (EG). Fifty-one in vivo-produced canine blastocysts were randomly allocated in two groups: GLY (n = 26) and EG (n = 25). After thawing, embryos from M0 were immediately stained with the fluorescent probes propidium iodide and Hoechst 33 342 to evaluate cellular viability. Frozen-thawed embryos from M3 and M6 were cultured in SOFaa medium + 10% FCS at 38.5°C under an atmosphere of 5% CO(2) with maximum humidity, for 3 and 6 days, respectively, and similarly stained. The blastocoele reexpansion rate (24 h after in vitro culture) did not differ between GLY (76.5%) and EG (68.8%). Post-thaw viable cells rate were not significantly different between GLY and EG (66.5 ± 4.8 and 57.3 ± 4.8, respectively, mean ± SEM), or among M0 (62.3 ± 5.7%), M3 (56.9 ± 6.0%), and M6 (66.5 ± 6.0%). In conclusion, canine blastocysts cryopreserved by slow freezing in 1.0 m glycerol or 1.5 m ethylene glycol, had satisfactory blastocoele reexpansion rates, similar post-thawing viability, and remained viable for up to 6 days of in vitro culture.

Reproduction of the female ferret (Mustela putorius furo)

The domestic ferret is a seasonally polyoestrous species. Females reach puberty at the age of 8-12 months. Females exhibit a constant oestrus between late March and early August if they are not bred. Increasing tumescence in the pink-coloured vulva is a sign of pro-oestrus. Oestrus can persist for up to 5 months, but once ovulation is induced, either pregnancy or pseudopregnancy ensues. Follicular development and atresia overlap in such a manner that there is a recent cohort of follicles available for ovulation whenever copulation might occur. Copulation may last from 15 min to 3 h, the average being 1 h. Ovulation is induced by pressure on the cervix associated with copulation. After sufficient LH release, the pre-ovulatory follicles mature and an average of 12 oocytes (5-13) per female are ovulated 30-40 h after copulation into the ovarian bursa. The ferret oocytes are most capable of being fertilized up to 12 h after ovulation, i.e. 42-52 h after copulation. Ferret oocytes ovulate at the metaphase of the second meiotic division (MII) embedded in three layers of corona radiata cells. Embryos enter the uterus over a period of several days starting on day 5 after mating. Between days 12 and 13 after mating, the embryos have become implanted in the endometrium. Implantation in the ferret is central with rapid invasion of the uterine epithelium by the trophoblast over a broad area that eventually becomes a zonary band of endotheliochorial placenta. Gestation length is 41 days (39-42 days). The domestic ferret gives birth to an average of eight kits (1-18 kits), which weigh 6-12 g at birth.

Embryo development and embryo transfer in the European mink (Mustela lutreola), an endangered mustelid species

The European mink is an endangered Mustelidae species and thus requires effective conservation measures, although little is known about reproduction in this species. In particular, preimplantation development has not been studied and, therefore, embryonic development and the growth of embryos was documented in the present study for European mink using light and fluorescent microscopy. Embryos develop in the oviducts and then migrate into the uterus on Day 6 post coitum (p.c.) at the morula stage. Embryos expanded as blastocysts from Day 7 until implantation on Day 12 p.c. Based on these findings, the use of embryo transfer for a conservation programme for the European mink was evaluated. Embryos were flushed from European mink resource females and transferred into the uterine horns of recipient hybrid females (honoriks and nohoriks). These hybrids were obtained by mating European polecat males with European mink females and vice versa. A total of 40 embryos was transferred and 20 live kits were born. The rates of pre- and postnatal survival were 50% and 70%, respectively. Both male and female offspring were lighter at birth in the embryo transfer group compared with naturally born controls, but there was no difference at 3 months of age.

Early embryonic development and in vitro culture of in vivo produced embryos in the farmed European polecat (Mustela putorius)

Early embryonic development and in vitro culture of in vivo produced embryos in the farmed European polecat (Mustela putorius) was investigated as a part of an ex situ conservation program of the endangered European mink (Mustela lutreola), using the European polecat as a model species. The oestrus cycles of 34 yearling polecat females were monitored by visual examination of the vulval swelling and, to induce ovulation, the females were mated once daily on two consecutive days. Sixteen yearling males were used for mating. The females were humanely killed 3-14 days after the first mating and the uteri and oviducts were collected for embryo recovery. Uterine and oviductal flushings yielded a total number of 295 embryos, representing developmental stages from the 1-cell stage to large expanded and hatched blastocysts. On Day 3 after the first mating, only 1-16-cell stage embryos were recovered. Between Days 4 and 6 after the first mating, 1-16-cell stage embryos and morulae were found. The first blastocysts were recovered on Day 7 after the first mating. The first implanted blastocysts were detected on Day 11 after the first mating. A total number of 85 embryos were in vitro cultured after recovery. Blastocyst production rates for in vitro cultured 1-16-cell stage embryos and for morulae/compact morulae were 68 and 84%, respectively. For all cultured embryos, the hatching rate was 15%. The in vitro culture requirements for the preimplantation embryos of the farmed European polecat remain to be determined before further utilization of the technique.

Surgical transfer of in vivo produced farmed European polecat (Mustela putorius) embryos

Surgical embryo transfer of farmed European polecat (Mustela putorius) was investigated as part of an ex situ preservation project. The long-term objective of the project is to develop effective technology for ex situ conservation of the European mink (Mustela lutreola), which is a highly endangered aboriginal European species. Twenty European polecat females, which served as a model species for the European mink, were humanely killed 4-9 days after first mating and embryos were recovered from oviducts and uteri. Donor-recipient pairs (n = 16) were generated by mating the donors (n = 20) once a day for 2 consecutive days with fertile males and by mating the corresponding recipients (n = 16) on the same days with vasectomized males. An embryo recovery rate of 70% (200 recovered embryos/284 corpora lutea) was achieved from 20 donors. Morulae and blastocysts were recovered between Days 5 and 9 after first mating and were regarded as the best developmental stages for uterine embryo transfer. A total of 172 embryos were transferred surgically under general anaesthesia into the ovarian third of the left uterine horn of 16 recipients with a thin glass capillary. Eleven recipients (69%) produced 72 pups equivalent to an average success rate of 42% (72 pups/172 transferred embryos). The average litter size was 4.5 (range 0-9). These results with this model species, farmed European polecat, demonstrate the potential of embryo transfer as an effective method for the preservation of the endangered European mink (M. lutreola). These species are closely related and have a similar reproductive physiology. However, success of applying embryo transfer in conserving European mink is still dependent on further studies both into its reproductive physiology and developing of improved flushing techniques for anaesthetized donors and the successful transfer of frozen-thawed embryos.

Successful embryo transfer in the silver fox (Vulpes vulpes)

Surgical embryo transfer in the silver fox was investigated as part of a larger project concerning the conservation of endangered canine species using modern artificial reproduction techniques with the farmed fox as a model. The animals were chosen on the basis of synchrony in natural oestrus. The timing of ovulation and artificial insemination was determined by measuring electrical resistance in the vagina. Twenty-nine embryos were flushed from eight humanely killed donor females and transferred surgically into the uteri of eight recipients. One recipient female gave birth to two male pups 47 days after the transfer of four expanded blastocysts and one embryo at the 16-cell stage derived from a donor female flushed 10 days after artificial insemination.

Longitudinal fecal steroid excretion in maned wolves (Chrysocyon brachyurus)

This study used a fecal steroid monitoring technique to evaluate reproductive cycles in male (4) and female (15) maned wolves, endangered South American canids. A radiolabeled testosterone infusion on a male revealed a fast and predominantly fecal route of excretion for this steroid. Testosterone was also excreted as eight unidentified metabolites, which was not the primary form of this steroid quantified in our assays. Fecal steroid concentrations (estradiol, E2; progestins, P; testosterone, T) in males and acyclic, nonpregnant (pseudo-pregnant), and pregnant females were monitored over four breeding seasons (October-January). Significant differences were detected between longitudinal P profiles of cyclic and acyclic females during estrus, luteal phase, and after birth/end of pseudo-pregnancy. Concentrations of P were also significantly higher in pregnant, compared to nonpregnant females, from proestrus to the end of the pregnant luteal phase. Although levels of T were higher in males than in females throughout the breeding season, no cyclicity in male fecal T concentrations was detected. Values of fecal P, T, and the ratio P/T were useful for differentiating gender and detecting pregnancy in females. Similarities to available data on other canids and the management and conservation implications of these findings were discussed.