Embryo Transfer In Sheep Research Articles

Embryo transfer in sheep (Ovis aries), efficient and consistent framework in superovulation treatment

Embryo transfer in sheep (Ovis aries), efficient and consistent framework in superovulation treatment

Cryopreservation and Transfer of Sheep Embryos Recovered at Different Stages of Development and Cryopreserved Using Different Techniques.

This article presents data from experiments to determine the cryoresistance of Charollais sheep embryos, depending on the stage of embryo development and the method of freezing, as well as the results of embryo transfer. The study design consisted of a study on the cryopreservation of ewe embryos at different developmental stages (early, 2-8 blastomeric and late, at the morula/blastocyst stage), two cryopreservation protocols (slow freezing and ultra-fast vitrification), and embryo transfer of cryo- and fresh embryos. Embryos from Charollais sheep donors (n = 12) were recovered after induction of superovulation. The embryos were recovered surgically (laparotomy) on days 2 and 6 after insemination. Before there was transfer to recipients, part of embryos was cryopreserved using standard slow freezing and ultra-fast vitrification methods. The average ovarian response was 7.54 ovulations per donor, and 5.83 embryos per donor were collected. No effect of the cryopreservation method and embryo development stage on the preservation of the morphological structure of embryos was found. There were no significant differences in the survival rate of cryoembryos at different development stages, frozen using different techniques, and after transfer to recipients. Differences in cryoresistance between embryonic developmental stages in favor of the morula/blastocyst stage were found (survival after thawing 86.4% vs. 75.0% in early embryos). At different stages of development, the survival rate of fresh embryos (45.8%) compared to cryopreserved ones (30.2%) was significantly higher (p < 0.05), while among fresh ones, the best survival rate (50.0%) was observed after the transfer of morules and blastocysts.

Multiple ovulation and embryo transfer in sheep: Effects of embryo developmental stage and quality on viability in vivo under farm conditions.

Multiple ovulation and embryo transfer (MOET) technologies are integral to genetic improvement programs in the sheep industries. Despite the protocols being well established, previous findings regarding the effects of embryo properties on MOET success remain contradictory. The objective of this study was to determine the effects of embryo developmental stage and quality on embryo viability following transfer to recipient ewes. Data including details of 377 embryos collected from 45 Merino donor ewes were obtained from MOET trials conducted on three separate farms on day 6 after laparoscopic artificial insemination (AI). A total of 270 embryos were classified as being of transferrable grade (grade 1: n = 233; grade 2: n = 37). One or two transferrable grade embryos were transferred to each of 256 synchronised recipient ewes and pregnancy diagnosis was performed on day 36 after embryo transfer. Embryos at the hatched blastocyst stage tended to have greater viability in vivo compared to embryos at the late morula stage (59.0 ± 10.6% vs. 36.2 ± 9.7%; P = 0.083). The viability of grade 1 embryos was greater than that of grade 2 embryos (53.6 ± 7.8% vs. 35.9 ± 10.2%; P < 0.05). The results suggest that the success of the MOET trials was influenced by the transfer of embryos at the late morula stage, almost half of which were classified as grade 2 embryos. These findings highlight the importance of following strict embryo quality grading criteria to inform the most economical management of recipient ewes and maximize pregnancy outcomes.

Towards Improving the Outcomes of Multiple Ovulation and Embryo Transfer in Sheep, with Particular Focus on Donor Superovulation.

Considerable improvements in sheep multiple ovulation and embryo transfer (MOET)protocols have been made; however, unlike for cattle, MOET is poorly developed in sheep, and thus has not been broadly applicable as a routine procedure. The tightly folded nature of the ewe cervix, the inconsistent ovarian response to various superovulatory treatments, and the requirement of labor to handle animals, particularly during large-scale production, has limited the implementation of successful MOET in sheep. Moreover, several extrinsic factors (e.g., sources, the purity of gonadotrophins and their administration) and intrinsic factors (e.g., breed, age, nutrition, reproductive status) severely limit the practicability of MOET in sheep and other domestic animals. In this review, we summarize the effects of different superovulatory protocols, and their respective ovarian responses, in terms of ovulation rate, and embryo recovery and transfer. Furthermore, various strategies, such as inhibin immunization, conventional superovulation protocols, and melatonin implants for improving the ovarian response, are discussed in detail. Other reproductive techniques and their relative advantages and disadvantages, such as artificial insemination (AI), and donor embryo recovery and transfer to the recipient through different procedures, which must be taken into consideration for achieving satisfactory results during any MOET program in sheep, are also summarized in this article.

Use of oxytocin to attain cervical dilation for transcervical embryo transfer in sheep.

The aim of this work was to determine whether a cervical dilation protocol (CDP) composed of only oxytocin can be used to perform transcervical (non-surgical) embryo transfer in sheep (NSET) without affecting the viability of the corpus luteum (CL). Likewise, we evaluated whether a cervical transposing test with a Hegar dilator (CT Hegar test), performed at oestrous time, could be used to screen ewes for NSET (greater or lower chances to transpose the cervix). For that, oestrous and ovulation synchronization was performed in 25 Santa Inês ewes to induce the dioestrous condition. Animals went through the following CDP in a crossover design: E+OX, oestradiol benzoate (100µg intravenously [IV]) and oxytocin (100IU IV); OX, oxytocin (100IU IV); and SAL, saline solution (IV). Using a Hegar dilator, cervical transposing attempts were performed at oestrous (D0) and dioestrous time (D8). The viability of the CL (morphology, luteal blood flow and progesterone values) was evaluated by ultrasonography (colour Doppler and B-mode) and by serum progesterone measurement from D7 to D13. The cervical transposing rate was lower for the SAL group (64%; 16/25; p<.05) and did not differ between the E+OX (88%; 22/25, p>.05) and OX (84%; 21/25, p>.05) groups. No treatment affected the CL viability. The CT Hegar test showed a high sensitivity (85.7%-93.3%), satisfactory accuracy (72%-84%), low false-negative rate (6.7%-14.6%), but high false-positive rate (46%-66.7%). In conclusion, a CDP protocol composed exclusively of oxytocin can lead to good cervical transposing rates and does not affect the viability of the CL. In addition, a screening test (CT Hegar) performed at oestrus can identify ewes for which cervical transposing will likely not occur at NSET.

Conceptus loss in Santa Inês ewes carrying twin pregnancies by natural mating or embryo transfer

Commercial application of reproductive biotechnologies such as multiple ovulation and embryo transfer depends on its overall efficiency. Sheep embryo transfer is gradually gaining wider adoption, but pregnancy rates after embryo transfer remain lower than those derived from natural mating for most breeds. The work was aimed to evaluate embryonic and fetal losses in Santa Inês ewes carrying twin pregnancies by natural mating or embryo transfer. Ewes were subjected to synchronized natural mating by ram effect or used as recipients for embryo transfer. Ewes diagnosed as carrying twin pregnancies at day 25 were used in the experiment (n = 42). Conceptus viability was monitored by ultrasonography on days 30, 35, 40, 45, 50, and 55 after conception. Conceptus loss was similar (P > 0.05) within natural mating 11/42 (26.19%) and embryo transfer 14/42 (33.34%). However, overall embryonic loss (80.0%) was greater (P < 0.05) than fetal loss (20.0%), with no difference within groups The results allow the conclusion that conceptus loss after embryo transfer is similar to natural mating and occurs predominantly during the embryonic stages.

84 Effect of Embryo Stage and Cryopreservation Method on Pregnancy Rates Obtained Following the Transfer of In Vivo-Derived Ovine Embryos on Small-Scale Farms in Thailand

Assisted reproductive technologies including superovulation, laparoscopic AI (LAI), and embryo transfer (ET) are important tools for genetic improvement in the sheep industry. The present study aimed to determine the effects of embryo stage and cryopreservation method on field trial outcomes of embryo transfer on small-scale farms in Thailand. Black Dorper ewes (n = 16) were used as donors and mixed breed ewes (n = 21) were used as recipients. Donors were superovulated as previously described (Tríbulo et al. 2012 Theriogenology 77, 1679-1685, 10.1016/j.theriogenology.2011.12.013) and inseminated by LAI within 22 to 24 h after standing heat (Day 0). Donors females were flushed on Day 2 to recover 2- to 8-cell embryos (n = 8) or on Day 6 to recover blastocyst-stage embryos (n = 8). Recovered embryos were randomly cryopreserved by either slow freezing or vitrification methods. Into 21 recipients was inserted an intravaginal device impregnated with CIDR® that was left in place for 10 days. Those received 300 IU of pregnant mare serum gonadotropin (PMSG) on Day 9 and randomly assigned to receive embryos on either Day 2 or 6 after oestrus. Two- to 8-cell embryos were thawed and transferred into the ipsilateral oviduct (n = 1-5 embryos/recipient) on Day 2. Five recipients received 15 slow-frozen embryos and 5 received 13 vitrified embryos. Blastocyst stage embryos were thawed and transferred into the ipsilateral uterine horn (n = 1-4 embryos/recipient) on Day 6. Five recipients received 11 slow-frozen embryos and 4 received 7 embryos. Pregnancy diagnosis was determined by ultrasonography 45 days after embryo transfer. Pregnancy rate was calculated as the proportion of ewes with at least one pregnancy out of the total number of ewes that received embryos. Chi-squared analysis was used to determine the effects of embryo freezing technique and embryo stage on pregnancy rate (SAS 9.2, SAS Institute Inc., Cary, NC, USA). All donor ewes responded to the superovulation program (donor had 3 to 6 corpora lutea). The mean number of viable embryos recovered was 4.3 ± 2.4 and 3.1 ± 3.7 for Day 2 and Day 6, respectively. Nineteen of the 21 recipient ewes responded to the synchronization program and received embryos in the study. There was no effect (P &gt; 0.05) of embryo stage (5/10 = 50% v. 3/9 = 33.3% for 2- to 8-cell v. blastocyst, respectively) or cryopreservation method (4/10 = 40% v. 4/9 = 44.4% for slow-freezing and vitrification, respectively) on pregnancy rate following embryo transfer. Results of the present study suggest that similar pregnancy rates following embryo transfer in sheep under tropical conditions in Thailand can be obtained using either 2- to 8-cell embryos or blastocyst-stage embryos and with embryos that have been cryopreserved by slow-freezing or vitrification. Further research with larger numbers of animals is necessary to confirm the preliminary results of the present study.

236 SUPEROVULATION IN SHEEP WITH REDUCED INJECTION FSH/eCG PROTOCOLS FOLLOWED BY TRANSFER OF FRESH OR VITRIFIED EMBRYOS

The aim of this experiment was to compare a single FSH/eCG, or double FSH-0.5% hyaluronan/eCG injection protocol with a multiple FSH/eCG injection protocol on the superovulatory response and embryo production in sheep. In addition, the effect of vitrification of these embryos on the pregnancy rate following embryo transfer was evaluated. Eighty Dohne Merino ewes received an 8-day CIDR-S device (0.33 g P4; Zoetis, Florham Park, NJ, USA) plus 10 mg of FSH i.m. (Folltropin-V; Vetoquinol, Lavaltrie, QC, Canada) and 400 IU of eCG i.m. (Pregnecol; Vetoquinol) in 3 treatment groups. Group 1 (n = 21) received a single 10-mg FSH injection in saline and 400 IU of eCG in saline 2.5 days before CIDR withdrawal. Group 2 (n = 23) received 6.7 mg of FSH in hyaluronan (MAP-5, 50 mg; Vetoquinol) and 400 IU of eCG in saline 2.5 days before CIDR withdrawal and 3.3 mg of FSH in hyaluronan 0.5 days before CIDR withdrawal. Group 3 (n = 36) received 7 injections (am, pm) of FSH in saline (2.5, 2.0, 1.5, 1.5, 1.0, 1.0, 0.5 mg) starting 2.5 days before CIDR withdrawal and 400 IU of eCG in saline at the first injection. Ewes were inseminated with semen collected from 1 of 5 rams at 36 to 40 h after CIDR withdrawal. Donor ewes were slaughtered 6 days after AI (Day 0), CL were counted and ova/embryos were collected. Viable embryos were transferred in singles into Day 6 synchronised recipients as either fresh (n = 128) or following vitrification/thawing using the CVM (CryoLogic, Blackburn, VIC, Australia; n = 97; Fry et al. 2005 Reprod. Fertil. Dev. 17, 243). Pregnancy was diagnosed by ultrasound scanning on Day 45. Data for CL and transferable embryo were analysed by the Kruskall-Wallis test and differences between groups determined by the Dunn test. Data for pregnancy rates was compared by chi-squared analysis. The mean number of CL in Groups 2 and 3 were both significantly higher than that in Group 1 (12.3 and 12.0 v. 8.5; P &lt; 0.05). Similarly, the total number of embryos/ova recovered in Groups 2 and 3 were significantly higher than for Group 1 (8.3 and 7.0 v. 5.0; P &lt; 0.05). Group 3 produced more viable embryos than either Group 2 or Group 1 (4.6 v. 2.7 and 2.1; P &lt; 0.05); however, data were skewed by the extensive use of semen from one ram in Group 2 that had a low fertilization rate (28%). The transfer of vitrified/thawed embryos resulted a nonsignificant (P &gt; 0.05) 10% decrease in pregnancy rate compared with fresh embryos (66% v. 76%). In conclusion, the administration of the sustained release FSH-MAP-5 in a 2-injection protocol in sheep was as effective as a multiple FSH injection protocol in inducing an ovarian response but more research is required to elucidate the effect of FSH-MAP-5 on embryo quality. The successful vitrification of sheep embryos provides a promising technique for the storage and transport of embryos in large-scale sheep embryo transfer programs.

Effects of Environment on Gestation Ratio of Sheep Embryo Transfer and its Control Measures

There are a lot of factors affecting the gestation ratio of sheep embryo transfer, and among them, environmentalcondition is an important one. We should provide the transferred embryos a better environmental condition fortheir survival and growth to increase the gestation ratio of sheep embryo transfer.

92 CRYOTIPS: A SIMPLE VITRIFICATION TECHNIQUE FOR SHEEP AND GOAT EMBRYOS

Vitrification procedure for embryos has not been used massively because there is not a standard protocol according to species. We evaluated reproductive efficiency of vitrified embryos in plastic tips of micropipettes. Estrous cycles of 36 Criolla goats (donors, n = 10; recipients, n = 26) and 48 Merino sheep (donors, n = 10; recipients, n = 38) were synchronized by sponges containing 60mgof MAP (Progespon®). At sponge removal (goats, Day 18; sheep, Day 14), recipients received 200 UI of eCG (Novormon®, Syntex, Argentina). Sheep and goat donors were superovulated with a total of 80 (igpFSH (Folltropin V®, Bioniche, Canada) every 12 h in 6 decreasing doses (18, 18, 14, 14, 8, 8) during the last 3 days of progestagen treatment. A dose of eCG (200 UI, Novormon®) was applied at progestagen removal. Donors of both species were inseminated by laparoscopy with frozen/thawed semen (200 × 106 spz) 12 to 14h after the onset of estrus. Embryo recovery was done by surgical prepubic laparotomy, and uterine horns were flushed with PBS + 10% SFB at Day 8 after sponge withdrawal. Before vitrification, embryos were kept in commercial embryo holding medium (Syngro, Bioniche, USA) at 25°C. Vitrification solutions were prepared using holding solution (HS) contents, PBS + 20% FBS. Embryos were maintained at 25°C and processed according to the following procedures: (1) HS + 10% glycerol (G) for 5 min, (2) HS +10% G + 20% ethylene glycol (EG) for 5 min, and (3) HS + 25% G + 25% EG for 30 s. Embryos were aspirated in 1 μL of solution 3, into the center of a plastic micropipette tip (0.36 mm inner diameter), and plunged into a cryotube filled with liquid nitrogen. Before embryo transfer, tips were warmed with fingers for 10 s and immersed in 4 dilution steps during 5 min each with 2.5 mL of HS containing (1) 12.5% G+ 12.5% EG+ 0.5 M of sucrose (S), (2) 0.5 M S, (3) 0.25 M S, and (4) HS alone at 25°C. In both species, at Day 8 after sponge withdrawal, 2 embryos of similar stage were transferred. Under laparoscopy view, the tip of the uterine horn was exteriorized by a nontraumatic clamp, through a 1-cm-long midline incision. The embryos were placed into the uterine lumen after punction and the uterine horn was allowed to return to the abdomen (semi-laparoscopic technique). Pregnancy was diagnosed by ultrasonography (Aloka 500) at Day 28 after being transferred. Reproduction efficiency in both species is shown in Table 1. This technique proves to be simple and efficient for both ovine embryo stages but only for goat blastocysts and can be used by veterinarians in field conditions at a very low cost. Differences of morulae survival between species require further study. Table 1.Reproductive efficiency after vitrified/warmed embryo transfer in sheep and goats according to the embryo stage

Large-Scale Field Practice of Juvenile In Vitro Embryo Transfer in Sheep.

Large-Scale Field Practice of Juvenile In Vitro Embryo Transfer in Sheep.

Early Pregnancy Diagnosis by Serum Progesterone and Ultrasound in Sheep Carrying Somatic Cell Nuclear Transfer‐Derived Pregnancies

Early pregnancy diagnosis and monitoring play an important role following embryo transfer in sheep. The aims of the current study were to investigate (i) the pattern of serum progesterone profiles in sheep carrying somatic cell nuclear transfer (SCNT)-derived (clone) pregnancies, and (ii) the frequency of pregnancy loss during development following SCNT embryo transfer. Sheep SCNT embryos were made using standard nuclear transfer techniques. Day 7 embryos were surgically transferred to oestrus-synchronized recipients (n = 27). As a control, normal fertile ewes (n = 12) were bred by natural breeding. Serum was collected from all the ewes on the day of estrus (day 0 sample), 7 days post-estrus (day 7 sample) and 19 days post-estrus (day 19 sample) and every 10 days thereafter until lambing or pregnancy loss occurred. Serum progesterone (P4) was assessed using enzyme immunoassay. Pregnancy was confirmed by ultrasound scanning on day 35 of pregnancy followed by subsequent scanning every 10 days. In control ewes, pregnancy rate on day 35 was 83.3% (10/12), whereas in the ewes that received SCNT embryos, it was 22.2% (6/27; p < 0.05). The day 45 pregnancy rate in the control ewes was 83.3%, whereas in the SCNT embryo recipients it was 11.0% (p < 0.05). Hormone analysis revealed that SCNT embryo recipients exhibited a significantly lower P4 profiles at different time points in pregnancy compared to controls (p < 0.05). This study highlights the use of serum progesterone in combination with ultrasound for the investigation of embryo loss and crucial times during development of normal and SCNT embryos in sheep. Further, the serum P4 levels directly reflect the degree of placental development in these two groups.

Features of follicle-stimulating hormone–stimulated follicles in a sheep model: keys to elucidate embryo failure in assisted reproductive technique cycles

To evaluate the individual functionality of gonadotropin-stimulated preovulatory follicles, for understanding embryo failure in assisted reproductive technique cycles, in a sheep model. Observational, model study. Public research unit. Fifteen adult Manchega ewes. Synchronization of the estrous cycle with intravaginal progestagens and ovarian stimulation with FSH; evaluation of reproductive activity, plasma sampling, ovarian ultrasonography, and ovariectomies. Determination of estrus behavior, plasma and intrafollicular concentrations of E(2) and inhibin A, number and size of ovarian follicles, and developmental competence of oocytes. These results support the usefulness of serial measurements of plasma inhibin A for assessment of follicular growth during the FSH treatment, rather than of E(2) assays commonly used. Functionality of FSH-stimulated preovulatory follicles is clearly disturbed, as confirmed by a negative correlation between follicular size and intrafollicular concentrations of inhibin A and E(2) in preovulatory follicles after individual dissection; moreover, the ability of their oocytes to resume meiosis was diminished. Functionality of follicles in controlled ovarian stimulation (COS), and developmental competence of their oocytes, is disturbed by the high doses of gonadotropin supplied and finally determined by follicular sizes at starting FSH treatment.

Multiple factors affecting the efficiency of multiple ovulation and embryo transfer in sheep and goats

This review offers an overview of the basic characteristics of in vivo embryo technologies, their current status, the main findings and the advances gained in recent years, and the outstanding subjects for increasing their efficiency. The use of superovulation and embryo transfer procedures remains affected by a high variability in the ovulatory response to hormonal treatment and by a low and variable number of transferable embryos and offspring obtained. This variability has been classically identified with both extrinsic (source, purity of gonadotrophins and protocol of administration) and intrinsic factors (breed, age, nutrition and reproductive status), which are reviewed in this paper. However, emerging data indicate that the main causes of variability are related to endocrine and ovarian factors, and so the number of studies and procedures addressing a better understanding and control of these factors may be increased in the future. The accomplishment of this objective, the improvement of procedures for embryo conservation and for the selection and management of recipient females, will allow further development and application of this technology.

New technology for vitrification and field (microscope-free) warming and transfer of small ruminant embryos

This study was designed to test the efficiency of recently developed vitrification technology followed by microscope-free thawing and transfer of sheep embryos. In a first set of experiments, in vivo derived embryos at the morula to blastocyst stage were frozen in an automated freezer in ethylene glycol, and after thawing and removal of cryoprotectants, were transferred to recipient ewes according to a standard protocol (control group). A second group of embryos were loaded into open-pulled straws (OPS) and plunged into liquid nitrogen after exposure at room temperature to the media: 10% glycerol (G) for 5 min, 10% G+20% ethylene glycol (EG) for 5 min, 25% G+25% EG for 30 s; or 10% EG+10% DMSO for 3 min, 20% EG+20% DMSO+0.3 M trehalose for 30 s. The OPS were thawed by plunging into tubes containing 0.5 M trehalose. After this rapid thawing, the embryos were directly transferred using OPS as the catheter for the transplantation process. In a second set of experiments, in vivo derived and in vitro produced expanded blastocysts were vitrified in OPS and then transferred as described above. The lambing rates recorded (59% for the conventionally cryopreserved in vivo derived embryos, 56% for the vitrified in vivo derived embryos, and 20% for the vitrified in vitro produced embryos), suggest the suitability of the vitrification technique for the transfer of embryos obtained both in vivo and in vitro. This simple technology gives rise to a high embryo survival rate and will no doubt have applications in rearing sheep or other small ruminants.

Successful direct transfer of vitrified sheep embryos

The use of a simple cryopreservation method, adapted to direct transfer of thawed embryos may help to reduce the costs of embryo transfer in sheep and increase the use of this technique genetic improvement of this species. Two experiments were made to test a vitrification method that is easy to apply in field conditions. All embryos were collected at Day 7 of the estrous cycle of FSH-stimulated donor ewes and were assessed morphologically, washed in modified PBS and incubated for 5 min in 10% glycerol, for 5 min in 10% glycerol and 20% ethylene glycol and were transferred into the vitrification solution (25% glycerol and 25% ethylene glycol). All solutions were based on mPBS. Embryos were loaded in straws (1 cm central part, the remaining parts being filled with 0.8 M galactose in mPBS) and plunged into liquid N2 within 30 sec of contact with the vitrification solution. The straws were thawed (10 sec at 20°C) and the embryos were either transferred directly or after 5 min of incubation in the content of the straw (followed by washing in PBS) into the uterus of a recipient ewe. In Trial 1, the pregnancy rates at term (72 vs. 72%) as well as the embryo survival rates (60 vs 50% respectively) were not different between fresh (n = 48 embryos) and vitrified (n = 50) embryos. In a second trial no difference was observed between vitrified embryos transferred after in vitro removal of the cryoprotectant (n = 86 embryos) or directly after thawing (n = 72) both in terms of lambing rate (67 vs. 75%, respectively) and embryo survival rate (lambs born/embryos transferred; 49 vs. 53%). This method of sheep embryo cryopreservation provided high pregnancy and embryo survival, even after direct transfer of the embryos.

Lionel Edward Aston Rowson, O.B.E. 28 May 1914 — 26 July 1989

L.E.A. Rowson was always known as Tim to his family, friends and colleagues alike. He was a veterinary surgeon who made important contributions to research in reproductive physiology in farm animals and its application to animal breeding. In particular, he was a pioneer of artificial insemination (AI) and embryo transfer, which have become two of the most important technologies for livestock improvement in modern times.He was appointed Director of the first AI centre for cattle breeding in Britain, established at Cambridge in 1942, and played a leading role in the application and rapid growth of this technology. In 1952 he contributed to the development of successful methods for the freezing and long-term storage of bull semen at very low temperatures. This had far-reaching consequences for the future of AI and cattle breeding worldwide.For thirty years he also worked at the Animal Research Station in Cambridge on methods for embryo transfer in sheep and cattle and their use in research and breeding. This culminated in the 1970s with the development of effective methods for collection and transfer of cattle embryos by non-surgical means. The birth of the first calf after transfer of a deepfrozen embryo in 1973 was another landmark, and these advances led quite quickly to the commercial application of embryo transfer in cattle breeding.Tim Rowson is generally regarded as the founder of embryo transfer in farm animals, but important contributions were made by many collaborators. He always considered that he was privileged during his early years to have worked with Dr John (later Sir John) Hammond, F.R.S., who maintained that the function of applied science was to synthesize the detailed knowledge gained from fundamental research into a constructive whole so that it could be used for a specific purpose. Tim was a true disciple of this philosophy and always tried to relate a fundamental approach to a practical outcome.

Estradiol-17 beta-oxytocin-induced cervical dilation in sheep: application to transcervical embryo transfer.

Experiments were conducted to determine whether exogenous estradiol-17beta (E2) and oxytocin (OT) can be used to improve transcervical (TC) embryo transfer (ET) procedures for sheep. Our concerns that the E2-OT treatment may alter luteal function prompted Exp. 1, in which 32 ewes were assigned to treatments in a 2x2 factorial array. On d 7 after onset of estrus, ewes received i.v. either 100 microg of E2 or diluent; 12 h later, ewes received i.v. either 400 USP units of OT or saline. To monitor luteal function, progesterone was measured in jugular blood collected from d 7 to 18. The treatments did not affect progesterone concentrations. Two trials were conducted in Exp. 2. In Trial 1, ewes were assigned to one of three treatments: TC transfer with E2-OT treatment to dilate the cervix, laparoscopic ET with E2-OT treatment, or laparoscopic ET with an equivalent diluent that did not dilate the cervix. In Trial 2, ewes were assigned to treatments in a 2x2 factorial array: TC or laparoscopic ET on d 6; E2-OT treatment for cervical dilation or diluents on d 6. Transferred embryos were recovered on d 12 in Trial 1 and d 14 in Trial 2, evaluated morphologically for development, and scored. Treatments did not affect the percentage of transferred embryos recovered. However, mode of transfer decreased (P<.01) the mean embryo development score. The E2-OT treatment increased (P<.01) the development score of embryos transferred transcervically, indicating that cervical dilation may improve the chances of embryos surviving after TC transfer. In conclusion, E2-OT treatment did not affect luteal function, and the E2-OT treatment can be used to enhance the success of TC embryo transfer in sheep.

Practical experiences with sheep embryo transfer

Practical experiences with sheep embryo transfer

Pregnancy rate after the transfer of sheep embryos originated from randomly chosen oocytes matured and fertilized in vitro

Randomly chosen sheep oocytes isolated from 2- to 5-mm follicles of hormonally nonstimulated slaughtered females were matured and fertilized in vitro. Using heparin for the induction of ram sperm capacitation, a fertilization rate close to 80% was recorded. After the transfer of 29 embryos cultured to the 2- to 4-cell stage to 4 recipients, each delivered 1 lamb. In another experiment, 34 2-cell embryos stage were transferred (1 to each oviduct) to 17 synchronized recipients; 8 pregnancies were established and each of 5 recipients delivered a single lamb. The remaining 3 recipients aborted at the third month of gestation. These results show that sheep embryos can be produced in vitro from randomly chosen oocytes and by using relatively simple procedures. However, the viability of the embryos was low, with approximately only 15% developing to term after transfer at the 2-cell stage.