Nutrition, synchronization, and management of beef embryo transfer recipients

A commercially viable cattle embryo transfer industry was established during the early 1970s. Initially, techniques for transferring cattle embryos were exclusively surgical. However, by the early 1980s, most embryos were transferred nonsurgically. For an embryo transfer program to be effective, numerous factors need to be in place to ensure success. Nutrition, estrous cycle control, and recipient management are all responsible for the success or failure in fertility for a given herd. Utilization of body condition scores is a practical method to determine nutritional status of the recipient herd. Prepartum nutrition is critical to ensure that cows calve in adequate body condition to reinitiate postpartum estrous cycles early enough to respond to synchronization protocols. Estrus synchronization for embryo transfer after detected estrus or for fixed-time embryo transfer without estrus detection are effective methods to increase the number of calves produced by embryo transfer. In addition, resynchronization of nonpregnant recipients effectively ensures that a high percentage of recipients will return to estrus during a 72 h interval and are eligible for subsequent embryo transfers. Numerous additional factors need to be assessed to ensure that the recipient herd achieves its reproductive potential. These factors include assessing the merits of nulliparous, primiparous, or multiparous cows, ensuring that facilities allow for minimal stress, and that the herd health program is well-defined and followed. Numerous short- and long-term factors contribute to recipients conceiving to a transferred embryo, maintaining the embryo/fetus to term, delivering the calf without assistance and raising and weaning a healthy calf.     

Factors affecting pregnancy rate following nonsurgical embryo transfer in buffalo (Bubalus bubalis): a retrospective study

The objectives of this study were to determine the pregnancy rate and factors affecting it following nonsurgical embryo transfer in buffalo. Donor buffalo were superovulated with FSH, and embryos collected nonsurgically were evaluated for stage of development and quality. They were transferred nonsurgically to 91 recipients on Days 5 to 7 of the natural (n = 52) or induced (n = 39) estrus (estrus = Day 0). The overall pregnancy rate of 24/91(26.4%) was higher than in earlier reports for buffalo but was much lower than in cattle. Pregnancy rates were not affected by season (autumn vs winter), side of transfer (right vs left uterine horn), or type of estrus (spontaneous vs induced). The pregnancy rate was high 11/27(40.7%) when donors and recipients were closely synchronized, while it was compromised when recipients were in estrus at +12 h (1/7, 14.3%) and at -12 h (5/27, 18.5%). Asynchrony beyond 12 h on either side resulted into conception failure. The pregnancy rate tended to increase with the increase in CL size of recipients, while stage of embryonic development had no effect. The transfer of an 8-cell embryo with a 16-cell embryo led to the birth of heterosexual twins, indicating that the uterine milieu of Day 5 to 6 recipients may be tolerated by the out-of-phase 8-cell embryo, at least in the presence of a more mature embryo. Embryo quality had the greatest effect on pregnancy rate as it was higher (P < 0.005) after the transfer of Grade I than Grade III embryos (6/10, 60.0% vs 3/36, 13.9%). Assessment of returns to estrus indicated that among nonpregnant recipients, 17/67 (25.4%) embryos never matured sufficiently to prevent luteolysis through maternal recognition of pregnancy (MRP), while 14/67 (20.8%) embryos probably died following MRP. These results indicate that efforts to increase pregnancy rate following embryo transfer in buffalo should include prevention of luteolysis during the first week of transfer and a reduction in the incidence of embryonic mortality.     

Advanced reproductive technology in the water buffalo

Embryo transfer techniques in water buffalo were derived from those in cattle. However, the success rate is much lower in buffaloes, due to their inherent lower fertility and poor superovulatory response. The buffalo ovary has a smaller population of recruitable follicles at any given time than the ovary of the cow (89% fewer at birth). In addition, estrus detection is problematic. Progress in the field of embryo transfer in water buffalo has been slow, and is primarily due to a poor response to superovulation. The average yield of transferable embryos is less than one per superovulated donor. In vitro embryo production could considerably improve the efficacy and logistics of embryo production. The technique of Ovum Pick Up is superior to superovulation; it can yield more transferable embryos per donor on a monthly basis (2.0 versus 0.6). The feasibility of intergeneric embryo transfer between buffalo and cattle has been investigated. No pregnancy resulted after transfer of 13 buffalo embryos to synchronized Holstein heifers. Preliminary successes with nucleus transfer of Bubalus bubalis fetal and adult somatic nuclei into enucleated bovine oocytes and subsequent development to the blastocyst stage have been reported.     

Successful transfer of vitrified Ilama (Lama glama) embryos

The exploitation of the domestic animals species of South American camelids is of great social importance for the native people living in the High Andes. The reproductive physiology of these species is a unique challenge in the development of advanced breeding techniques. At present, the cryopreservation of embryos has not been developed and very few investigations have been conducted. The objective of the present work was to evaluate the in vivo survival of vitrified llama embryos after transfer to recipient females. Donors females were treated with a CIDR-estradiol benzoate-eCG regimen and were mated naturally 6 days after CIDR withdrawal. One ovulatory dose (8 microg) of GnRH was administered immediately after mating. A second mating was allowed 24 h later. Embryo recovery was performed nonsurgically between 8 and 8.5 days after the first mating. Twenty-two ova/embryos were recovered from 12 donor females. Hatched blastocysts were exposed to vitrification solution (20% glycerol + 20% ethylene glycol + 0.3 M sucrose + 0.375 M glucose + 3% polyethylene glycol (P/V)) in three steps, and after loading into 0.25 ml straws, were plunged into liquid nitrogen. For embryo transfer, recipients animals were ovulation-synchronized using GnRH administered at the same time as donors. A total of eight vitrified-warmed embryos and 12 fresh embryos were nonsurgically transferred to four and six recipient females, respectively (two embryo per recipient). The pregnancy rates were 50 and 33.3% for recipients that had received vitrified embryos and fresh embryos, respectively. The results demonstrated the effectiveness of this simple vitrification method for cryopreservation of llama embryos.     

Buffalo and cattle hybrid embryo development is decreased by caffeine treatment during in vitro fertilization

Water buffalo are renowned for difficulties in the implementation of assisted reproductive technologies, with both males and females being problematic. In this study, we used cattle oocytes to assess the effect of treatments with heparin and caffeine on buffalo spermatozoa and subsequent fertilization and embryo development in vitro. There was no significant difference between buffalo and bovine spermatozoa in the events associated with fertilization. Fertilization of cattle oocytes with buffalo spermatozoa resulted in 7.8% of oocytes developing into hybrid embryos. A difference in the developmental capability of hybrid embryos compared with the cattle control was observed. This has not been previously reported. The subsequent transfer of a limited number of hybrid embryos did not produce a viable pregnancy. However, control treatments in this experiment also failed to achieve pregnancy, so objective data is not available to provide conclusions about the developmental competence of the buffalo and cattle hybrid embryos. Optimal spermatozoa capacitation treatments achieved 61% fertilization and 21% zygote cleavage into two cell embryos. There was no significant difference in fertilization or development due to heparin or spermatozoa concentrations. However, treatment of buffalo and cattle spermatozoa with caffeine significantly decreased embryo cleavage but also tended to decrease embryo development to the blastocyst stage. These studies suggest that problems with reproduction in buffalo may reside with biological mechanisms associated with the oocyte that are often complicated by poor male reproductive performance. Selection for bull fertility would prevent some of these complications.     

Bovine embryo morphology and evaluation

The following paper briefly reviews the morphology of the bovine embryo and presents a retrospective analysis of bovine embryo transfer results accumulated from April to December of 1982 at a commercial embryo transfer center. Of particular interests were bovine embryo morphology, assessment of embryo quality, and recipient-donor, recipient-embryo synchrony requirements. Embryos were recovered from superovulated donors five to nine days after estrus (estrus = day O). All embryos were individually examined at 200X for cell stage of development and embryo quality. Embryos were nonsurgically transferred to recipients that were within two days of estrous cycle synchrony with the donor. Attempts were made to synchronize estimated developmental age of embryos to the day of the recipient cycle. A high degree of variability was observed in morphological development and embryo quality within and among donors. Embryo recovery in individual donors resulted in a wide range of embryonic cell stages, often differing in estimated developmental ages from 24 to 48 hours. A total of 783 embryos were transferred, resulting in 308 pregnancies. Stage of embryonic development (16-cell through hatched blastocyst) had little effect on pregnancy rates. Embryo quality was a more accurate predictor of success. Embryos of excellent, good, fair and poor categories resulted in 45%, 44%, 27% and 20% pregnancy rates, respectively. Recipient-donor estrous cycle synchrony of two days in either direction did not significantly alter pregnancy rates. However, 88% of 258 pregnancies (584 total transfers) occurred with a +/-1 day recipient-embryo synchrony compared to 74% based on +/-1 day recipient-donor cycle synchrony (P<0.001). Results suggest that transfer of bovine embryos based on synchrony between day of recipient cycle and state of embryonic development provides higher pregnancy rates than transfers based on recipient-donor cycle synchrony.     

A one-step method for direct nonsurgical transfer of frozen-thawed bovine embryos

One impediment to the more widespread use of freezing as an adjunct to embryo transfer in cattle has been the method used to remove the protective compound from the thawed embryos. Recently, a method has been developed that permits bovine embryos to be diluted out of the protective solution within the plastic straw in which the embryos were originally rrozen and thawed. The method requires only about 10 minutes to perform and does not require a microscope or other laboratory equipment. Therefore, frozen bovine embryos can be thawed, diluted, and transferred nonsurgically into recipient cattle under conditions quite similar to those used for artificial insemination. A large number of field trials of this method have been performed during the past 2 1 2 years. A total of 327 pregnancies have been established by the nonsurgical transfer of 1259 embryos that had been frozen, thawed, and diluted by this method.     

Artificial induction of twinning in cattle by means of supplemental embryo transfer

The induction of twins by surgical and nonsurgical transfer was performed 6 - 8 days after Artificial Insemination (A.I.) in a total of 142 cows. Of the 47 heifers, which received surgically transferred embryos, 32 (68%) became pregnant. Of the 95 cows, which received nonsurgically transferred embryos, 58 (61,6%) became pregnant. A total of 90 (63.5%) of the recipient animals became pregnant. Up to date 64 recipients have calved; twins have resulted in 40 and 48,2% resp, from surgical and nonsurgical inductions. Out of a total of 64 calvings 29 (45,3%) were twins, and of these 38% were males, 27% were females, and 34% were mixed births. Female - calves resulted in freemartinism. There was no increase in the incidence of either retained placenta or dystocia. The induction of twinning by means of embryo transfer can be regarded as a useful method for the increase in the reproductive performance cattle.     

Quick-splitting of bovine embryos

Described is a simplified method of bovine embryo bisection amenable to on-farm embryo transfer. Using a microblade operated by a hand-held micromanipulator, Day 7 bovine embryos were bisected while in the zona pellucida. With a vertical motion, the embryo was pinned between the blade and the bottom of a plastic petri dish and bisected. Demi-embryos were transferred nonsurgically (without zonae pellucidae) into synchronized recipients. Pregnancy rates were normal with 5 13 (38%) and 9 20 (45%) of recipients confirmed pregnant 70 to 80 d after receiving either twin or single half embryos, respectively. This compared to 12 28 (43%) of recipients becoming pregnant from transfer of whole embryos. These data confirm that bovine demi-embryos do not need zonae pellucidae on Day 7 and that simplified field methods of bisection give normal pregnancy results.     

Development of embryos reconstructed by interspecies nuclear transfer of adult fibroblasts between buffalo (Bubalus bubalis) and cattle (Bos indicus)

The objective of this study was to explore the feasibility of employing adult fibroblasts as donor cells in interspecies nuclear transfer (NT) between buffaloes and cattle. Buffalo and bovine oocytes matured in vitro for 22 h were enucleated by micromanipulation using the Spindle View system. An ear fibroblast, pretreated with 0.1 microg/mL aphidicolin for 24 h, followed by culture for 2-9 days in Dulbecco's Modified Eagle's Media+0.5% fetal bovine serum, was introduced into the cytoplast by microinjection. Reconstructed oocytes were activated by exposure to 5 microM ionomycin for 5 min and 2 mM 6-dimethylaminopurine for 3 h. When buffalo adult fibroblasts were used as donor cells, there were no differences (P < 0.75) in the cleavage rate (66.2% versus 64.0%) between bovine and buffalo recipient oocytes, but more embryos derived from bovine cytoplasts developed to blastocysts than from buffalo cytoplasts (13.3% versus 3.0%, P < 0.05). When bovine adult fibroblasts were used as donor nuclei, both cleavage rate (45.3%) and blastocyst yield (4.5%) of NT embryos derived from buffalo cytoplasts were lower than those of NT embryos derived from bovine cytoplasts (65.5 and 11.9%, P < 0.05). The proportion of parthenogenetic buffalo (29.1%) or bovine (35.6%) oocytes developing to blastocysts was higher than those of NT embryos (P < 0.01). Interspecies NT embryos were derived from the donor cells and 55.0-61.9% of them possessed a normal diploid karyotype. In conclusion, embryos reconstructed by interspecies NT of adult fibroblasts between buffaloes and cattle developed to blastocysts, but bovine cytoplasts may direct embryonic development more effectively than buffalo cytoplasts, regardless of donor cell species.     

Early pregnancy associated thrombocytopenia as an initial response to pregnancy in cattle

This study was conducted to determine if early pregnancy-associated thrombocytopenia exists in cattle as has been demonstrated in mice and in humans. Three experiments were designed to compare peripheral platelet counts in pregnant versus nonpregnant animals. In Experiment 1 heifers (n = 25) were artificially inseminated 12 h after the onset of estrus. Peripheral platelet counts in 19 pregnant versus 6 nonpregnant heifers did not reveal any significant differences between groups after insemination. In Experiment 2 embryos were collected nonsurgically from superovulated cows (n =18) on Days 6 to 7 after estrus. Platelet counts were monitored every 12 h after the first insemination until 60 h after the second insemination. Platelet counts and the number of embryos collected nonsurgically from these superovulated donors did not show any significant correlations (P>0.05). Ten recipient heifers synchronized to donor animals received either an unfertilized ovum or a good quality embryo via nonsurgical transfer into the uterus. There were no significant reductions in platelet counts after transfer. In Experiment 3 platelet counts were monitored daily in four pregnant and five nonpregnant recipient heifers between Day 0 and Day 30 after embryo transfer on Day 8 of the cycle. The platelet counts did not reveal any significant differences between the pregnant and nonpregnant groups throughout Days 0 to 30. These results indicate that early pregnancy-associated thrombocytopenia cannot be demonstrated in cattle. Peripheral platelet counts cannot be used as an indicator of early pregnancy in cattle.     

A procedure for successful nonsurgical embryo transfer in swine

The current study was undertaken to develop a successful procedure for the nonsurgical transfer of pig embryos. A total of 663 embryos were surgically collected on Day 4 or 5 from 55 donors, of which 542 embryos of acceptable quality were nonsurgically transferred to 46 recipients. Nonsurgical recipient gilts were sedated 15 min prior to transfer with 20 mg im acepromazine maleate. A disposable insemination spirette with an attached 3-way stopcock was manipulated into the cervix of each gilt. Embryos were expelled from a tomcat catheter into the spirette, and 10 to 12 ml of Whitten's medium were used to flush embryos through the spirette into the reproductive tract. Sixteen (34.8%) recipient gilts did not return to estrus before Day 36, and 10 (21.7%) gilts farrowed with an average litter size of 4.3 +/- 0.7. Embryos were collected from an additional 20 donors and were surgically transferred to an additional 19 recipients. Surgical transfers conducted at the same time as the nonsurgical transfers resulted in 12 (63.2%) gilts farrowing and 7.1 +/- 0.6 pigs were born per litter. In conclusion, a procedure has been developed for nonsurgical transfer of swine embryos which simplifies the process of embryo transfer and which may increase the potential for utilization of embryo transfer technologies by swine producers.     

Cryopreservation of canine embryos

The assisted reproductive techniques (ARTs) such as in vitro fertilization, embryo transfer, and cryopreservation of gametes have contributed considerably to the development of biomedical sciences in addition to improving infertility treatments in humans as well as the breeding of domestic animals. However, ARTs used in canine species have strictly limited utility when compared with other mammalian species, including humans. Although successful somatic cell cloning has been reported, artificial insemination by frozen semen to date is only available for the improved breeding and reproduction for companion and working dogs as well as guide dogs for the blind. We describe here the successful cryopreservation of embryos and subsequent embryo transfer in dogs. Canine embryos were collected from excised reproductive organs after artificial insemination and subsequently cryopreserved by a vitrification method. When the 4-cell to morula stage of cryopreserved embryos were nonsurgically transferred into the uteri of nine recipient bitches using a cystoscope, five recipients became pregnant and four of them delivered a total of seven pups. The cryopreservation of embryos in canine species will facilitate the transportation and storage of genetic materials and will aid in the elimination of vertically transmitted diseases in dogs. In addition, this technique will contribute to the improved breeding of companion and working dogs such as guide dogs, drug-detecting dogs, and quarantine dogs.     

Influence of environmental temperature on reproductive performance of bovine embryo donors and recipients in the southwest region of the United States

Superovulation and embryo transfer records on performance of embryo donor (n = 3,908; beef 99%, dairy 1%) and recipient (n = 19,936; beef 92%, dairy 8%) cattle from a commercial transfer unit were analyzed for environmental effects. Embryos (n = 42,428) were recovered on Days 5 to 8 postestrus from superovulated donors. Numbers of ova, fertilized ova and embryos of transferable quality were recorded. Transferable embryos were classified according to stage of development and morphological quality. Embryos (n = 19,936) were transferred nonsurgically. Responses were modeled with maximum-likelihood procedures using log-linear functions of independent variables and ANOVA. Fluctuations in daily maximum temperature (1 to 43 degrees C), for Days 0 to 7 of embryo development, had no effect on distribution of embryos classified as good (48%), fair (40%) and poor (12%). Temperature did not affect the percentage of donors flushed with recoverable ova (89%), mean number of ova (12.2 +/- 0.3), fertilization rate (76%) or percentage of transferable embryos (57%). Recipient pregnancy rate (56%) was not affected by mean maximum temperature for Days 0 to 10 posttransfer. Interactions between temperature and breed type (dairy vs beef), parity (cow vs heifer), or lactational status (lactating vs dry) on pregnancy rate were recorded. Elevated environmental temperature does not appear to adversely affect reproductive responses of donor and recipient cattle intensely managed in a commercial transfer unit.     

Intrauterine inoculation of seronegative heifers with bovine viral diarrhea virus concurrent with transfer of in vivo-derived bovine embryos

Bovine viral diarrhea virus (BVDV) has been shown to be associated with single transferable in vivo-derived bovine embryos despite washing and trypsin treatment. Hence, the primary objective was to evaluate the potential of BVDV to be transmitted via the intrauterine route at the time of embryo transfer. In vivo-derived bovine embryos (n = 10) were nonsurgically collected from a single Bos tarus donor cow negative for BVDV. After collection and washing, embryos were placed into transfer media containing BVDV (SD-1; Type 1a). Each of the 10 embryos was individually loaded into an 0.25-mL straw, which was then nonsurgically transferred into the uterus of 1 of the 10 seronegative recipients on Day 0. The total quantity of virus transferred into the uterus of each of the 10 Bos tarus recipients was 878 cell culture infective doses to the 50% end point (CCID₅₀)/mL. Additionally, control heifers received 1.5 × 10⁶ CCID₅₀ BVDV/.5 mL without an embryo (positive) or heat-inactivated BVDV (negative). The positive control heifer and all 10 recipients of virus-exposed embryos exhibited viremia by Day 6 and seroconverted by Day 15 after transfer. The negative control heifer did not exhibit a viremia or seroconvert. At 30 d after embryo transfer, 6 of 10 heifers in the treatment group were pregnant; however, 30 d later, only one was still pregnant. This fetus was nonviable and was positive for BVDV. In conclusion, the quantity of BVDV associated with bovine embryos after in vitro exposure can result in viremia and seroconversion of seronegative recipients after transfer into the uterus during diestrus.     

Non-surgical transfer of deep-frozen bovine embryos

Preservation of cattle embryos by methods of deep-freezing has recently been established (1, 11, 12) and provides a valuable addition to the possibilities of controlled breeding by embryo transfer in cattle.Already long distance transport of frozen embryos has been demonstrated (2, 6) and adopted by some commercial interests. However, in all publications to date, embryos have been transferred to recipients by surgical methods, even though non-surgical methods of embryo recovery and transfer would be preferred for commercial embryo transfer.The purpose of the present experiments was to utilize non-surgical methods of embryo recovery and transfer of deep-frozen cattle embryos to demonstrate the feasibility of the procedure for a farm service to interested breeders. The particular advantage of non-surgical embryo transfer methods is that neither the donor nor recipient need to leave the farm. Embryo preservation by freezing obviates the necessity for synchronization of recipients for immediate transfer from the donor and allows considerable freedom in the choice of the recipients and the timing of embryo transfers.     

Nonsurgical collection and nonsurgical transfer of preimplantation embryos in the domestic rabbit (Oryctolagus cuniculus) and domestic ferret (Mustela putorius furo)

The objective of this study was to develop nonsurgical methods of embryo collection and transfer in domestic rabbits (Oryctolagus cuniculus) and domestic ferrets (Mustela putorius furo) to serve as models for use in mammals in which surgical procedures are the usual means for applying embryo transfer technology. Specially designed transcervical catheters were used together with a fibre optic endoscope to visualize and then catheterize the rabbit and ferret cervices. Five consecutive transcervical uterine flushes in each of eight superovulated female rabbits 78-89 h after an ovulatory injection of LH resulted in the retrieval of 187 embryos, for an average of 23 embryos per rabbit. A total of 116 embryos were nonsurgically transferred to the uteri of ten recipients, and resulted in 23 young (20%). Eight rabbits (80%) produced young with an average litter size of 2.88 (range 1-7). Ten consecutive transcervical uterine flushes in each of 37 female ferrets 145-178 h after an ovulatory injection of hCG resulted in the retrieval of 324 embryos, an average of 8.76 embryos per ferret. A total of 251 embryos from 27 donors were nonsurgically transferred to the uteri of 31 recipients, and resulted in 65 young (26%). Twenty-eight of the recipients (90%) were initially pregnant, as indicated by postpartum necropsies, and twenty-two ferrets (71%) produced young. The average litter size was 2.95 (range 1-7). This is the first report of live births resulting from the nonsurgical collection of embryos from a donor followed by nonsurgical transfer of those same embryos to a synchronous recipient. The methods reported here can serve as models for use in other mammals in which direct visualization and manipulation of the cervix are not possible, and will be particularly useful in endangered species.     

Pregnancy rates and births after unilateral or bilateral transfer of bovine embryos produced in vitro.

Late morulae and blastocysts produced in vitro were nonsurgically transferred to heifers by unilateral (n = 184) or bilateral (n = 94) transfer. Of the recipients, 58% had serum progesterone values greater than 1.4 ng ml-1 on day 21 and rectal palpation on day 35 showed that 50% (138 of 278) were pregnant. The embryonic mortality rate between days 21 and 35 was estimated to be about 14% and between days 36 and 90 to be about 12%. Of the animals, 8% aborted between days 91 and 250 of pregnancy. No difference was observed in pregnancy rates between unilateral transfer of one (47%) or two embryos (49%) and bilateral transfer (53%), or in the twinning rate between bilateral transfer (42%) and unilateral transfer of two embryos (33%). The pregnancy rate was 54% with embryos evaluated as morphologically excellent or good, 51% with fair embryos and 26% with poor ones. A higher pregnancy rate (60%) was obtained after embryo transfer when the synchrony between recipient and embryo was -1 day.     

Compromised development of calves (Bos gaurus) derived from in vitro-generated embryos and transferred interspecifically into domestic cattle (Bos taurus)

Advanced reproductive technologies, incuding IVF and interspecies embryo transfer, are becoming increasingly important for the preservation of endangered species. Previous attempts at interspecies transfers between Bos gaurus and Bos taurus have yielded compromised offspring. The goal of this investigation was to characterize the effects of interspecies transfer of IVF-derived embryos on subsequent neonatal outcome. To achieve this goal, fresh Bos gaurus IVF-derived embryos were transferred into Holstein (Bos taurus) recipients. Four fetuses were carried to term. Calf weight, temperature, heart rate, and respiration rate were recorded after birth. Blood samples also were obtained for determination of blood glucose, pH, packed cell volume (PCV), total hemoglobin (tHB), PO2, and PCO2. After parturition, milk production and health status of the recipients were recorded. Two calves were alive at birth, and two calves were stillborn. One of the calves that was born alive died within minutes after birth, while the other lived until approximately 26 h of age. Blood samples obtained from the calf that lived for 26 h showed it to be extremely acidotic and hypoglycemic; this calf also had marked difficulty thermoregulating. At necropsy, all calves showed evidence of in utero gasping and hypoxia, suggestive of premature placental separation. None of the recipient cows showed typical signs of impending parturition. After parturition, lactogenesis in all recipient cows was markedly decreased. On gross examination, placentae resulting from the interspecies transfers had fewer cotyledons that were also much larger in size compared to cotyledons from normal gaur placentae. Calves in this study had abnormalities consistent with those noted from previous interspecies transfers and with IVF and nuclear transfer (cloned) calves. Due to the design of this study, it is not possible to differentiate between problems resulting from the IVF process and those resulting from potential interspecies incompatibilities. However, interspecies transfers of in vitro-produced gaur embryos into Bos taurus are strongly discouraged.     

Embryo quality and transcervical technique are not the limiting factors in donkey embryo transfer outcome

Embryo transfer (ET) in the donkey resulted in a very low recipient pregnancy rates. The aim of these studies was to investigate if nonsurgical transfer techniques or donkey embryo quality affect donkey recipient pregnancy failure. In Study 1, the impact of transfer technique was investigated by evaluating if cervical catheterization is associated with prostaglandin release and suppression of luteal function and if donkey recipients would become pregnant after nonsurgical transfer of horse embryos. Four jennies, from 5 to 8 d after ovulation, were submitted to a sham transcervical ET and to evaluation of PGFM and progesterone plasma concentrations. Five 8 d horse embryos were nonsurgically transferred into synchronized donkey recipients (HD). Cervical stimulation caused a transient PGF_2α release in two of four jennies in the absence of a significant decrease in progesterone plasma concentration. All transferred horse embryos resulted in pregnancies in the jenny recipients. In Study 2, donkey embryo viability was investigated by 1.2 meters, 6-diamidino-2-phenylindole (DAPI) staining of 10 embryos and by the transfer of 6 and 12 donkey embryos in synchronized mare (DH) and donkey (DD) recipients, respectively, of known fertility. The estimated proportion of dead cells in DAPI stained embryos was 0.9% (range 0-3.9%) and below what is considered normal (20%) for horse embryos. Three of six and six of 12 of the DH and DD ETs, respectively resulted in pregnancies at 14 and 25 d (50%), a higher pregnancy rate than previously reported after DD ET. The overall results of this study suggest that the transcervical technique for ET and donkey embryo viability are not the reasons for the low pregnancy rates that have previously been described in donkey recipients, and that nonsurgical ET in donkeys can result in acceptable results.