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

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.

Factors affecting the efficiency of embryo transfer in the domestic ferret (Mustela putorius furo)

Embryo transfer (ET) to recipient females is a foundational strategy for a number of assisted reproductive technologies, including cloning by somatic cell nuclear transfer. In an attempt to develop efficient ET in domestic ferrets, factors affecting development of transferred embryo were investigated. Unilateral and bilateral transfer of zygotes or blastocysts in the oviduct or uterus was evaluated in recipient nulliparous or primiparous females. Developing fetuses were collected from recipient animals 21 days post-copulation and examined. The percentage of fetal formation was different (P<0.05) for unilateral and bilateral transfer of zygotes (71%) in nulliparous females with bilateral transfer (56%) in primiparous recipients. The percentage (90%) of fetal formation in nulliparous recipients following unilateral transfer of blastocysts was higher (P<0.05) than that observed in primiparous recipients with bilateral ET (73%). Notably, the percentage of fetal formation was higher (P<0.05) when blastocyts were transferred as compared to zygotes (90% versus 71%). Transuterine migration of embryos occurred following all unilateral transfers and also in approximately 50% of bilateral transfers with different number of embryos in each uterine horn. These data will help to facilitate the development of assisted reproductive strategies in the ferret and could lead to the use of this species for modeling human disease and for conservation of the endangered Mustelidae species such as black-footed ferret and European mink.

Transfer of European mink (Mustela lutreola) embryos into hybrid recipients

The European mink is considered as a highly endangered Mustelidae species. The objective of this study was to explore the intriguing possibility of embryo transfer from European mink to closely related Mustelidae recipient females. To overcome interspecies pregnancy failure, embryos of European mink (Mustela lutreola) were transferred into hybrid females obtained after mating of European polecat (Mustela putorius) males and European mink (M. lutreola) females and vice versa. A total of 32 blastocysts were surgically flushed from the uteri of nine European mink donors and surgically transferred into six pseudopregnant hybrid recipients. One of the recipients received a single embryo and did not whelp. The remaining five recipients each received five to eight embryos and delivered kits. The overall success rate was 50% (16 kits/32 transferred embryos). For both male and female offspring, the average birth weight was lower in ET group when compared with naturally bred control population of European mink. The postnatal mortality rate was significantly higher in ET group as compared to controls: only 9 of 16 kits survived past the first week. At 10 days of age, the average weight for male offspring from the ET and control groups did not differ, although differences still persisted at this age for female offspring. At 3 months of age, the weight of male and female offspring in the ET group did not differ from European minks born after natural mating. We propose that transfer of European mink embryos to hybrid recipients be considered as a new experimental tool within the framework of ex situ approach conservation of this aboriginal European mustelid.

Live cubs born after transfer of OPS vitrified-warmed embryos in the farmed European polecat (Mustela putorius)

The Open Pulled Straw (OPS) method of vitrification has been used successfully for cryopreserving embryos of most domestic animal species. However, there is no report of a successful delivery of offspring after transfer of vitrified embryos in carnivores, even though vitrification has been a successful freezing method for species like swine whose embryos are known to be susceptible to chilling injury. Morulae and blastocysts of farmed European polecat (Mustela putorius) were vitrified and warmed before in vitro culture in modified synthetic oviductal fluid (SOF) for a period from a few hours up to 3 days before being transferred to recipients. Survival rate after vitrification, warming and in vitro culture was 51% (50/98). A total of 50 embryos were transferred surgically into the uteri of four anesthetized recipients. Two recipients delivered a total of eight offspring (2 and 6 each) for an overall survival rate of 16% (eight live cubs/50 transferred embryos). According to our knowledge, these offspring are the first carnivores produced by transfer of in vivo embryos after vitrification by OPS. Based on the present results, we suggest that OPS vitrification can be used as an alternative cryopreservation method for mustelid embryos with pup results comparable to conventional slow freezing.