Embryo transfer (ET) is a useful tool to achieve more progeny from one ewe or doe or a group than is possible in the usual lifetime of a female. The technique is also referred to as Multiple Ovulation and Embryo Transfer (MOET).
Donors might average 5 to 12 good embryos per flush
Donors can be reflushed every 2 months
Good embryos should become pregnancies 60% to 80% of the time
Freezing of embryos permits sale and implanting at any time.
DESCRIPTION OF THE PROCESS
Intra-vaginal Progestagen sponges or CIDR's are inserted in donor ewes for 12-14 days.
Before removal of sponges/CIDR's donor ewes get 6-8 injections over 3-4 days with FSH hormone (Follicle stimulating hormone). FSH in combination with PMSG or eCG (pregnant mare serum or equine chorionic gonadotrophin) stimulates follicular activity and at an appropriate stage of the reproductive cycle the release of multiple ova can be achieved in 60-90% of donor animals, so called multi-ovulation.
Fertilization of oocyte is achieved by laparoscopic intra-uterine insemination with good quality fresh diluted semen during the peak oestrus.
Flushing of embryos is done surgically 5½ to 6 days after insemination, with donor ewes under general anaesthesia. The uterine horns are exposed by laparotomy and by placing a two-flow Foley’s catheter at the base of each uterine horn, embryos are flushed from the tip (near the fallopian tube) downward
Pictured: Veterinarian Jean van Niekerk assisted by Andrea van Niekerk- performing the embryo flushing of a ewe.
Pictured: Ewe (uterus) being flushed.
Embryos are collected and kept in special media during the whole process. With the aid of a stereomicroscope, embryos are picked out of the media and classified as Grade I to Grade IV (transferable to non- transferable). The embryos go through multiple washings to ensure they are free from debris.
Pictured: Embryologist Moozie van Niekerk grading embryo's under the microscope.
The degree of response is related to the number of appropriate small follicles already present in the ovaries. The number of these can vary greatly between ewes – hence the variability of the responses obtained. Occasionally ewes “over-respond” to the stimulation. Too many follicles can often result in poor ovulation and poor or no fertilization. Some ewes and some breeds are particularly sensitive to the drugs and require dose adjustments to achieve more satisfactory results.
Recipient ewes are synchronised with donor ewes in order to match according to time of ovulation.
An alternative is to freeze and store embryos in liquid nitrogen to transfer later or to export.
Conception with freshly transferred embryos is better (65-90%) than frozen embryos (40-55%).
PRACTICAL APPLICATIONS FOR EMBRYO TRANSFER
Fast and effective genetic improvement of studs.
With proper records the stud breeder identifies the top ewes in his stud and with the MOET techniques the numbers of offspring from these proven ewes can be multiplied.
Export of genetic material.
Certain breeds of goats and sheep, especially Dorpers, are in great demand and already located in many countries. Murray River Genetics exports to many countries including Brazil, South Africa, Mexico, USA, China and is currently the only centre registered to export to the European Union.
THINGS TO KEEP IN MIND
There is no way of determining whether a donor ewe will react positively to a super ovulation program or not. Ewes with a previous lambing record are preferred.
Donor and recipient ewes must be in a positive growing phase at time of insemination and embryo flushing and/or embryo transfer.
Animals with a body condition score of between 2.5 and 3 are most ideal. Animals that are over- or under weight can react negatively to treatment.
Choose donor rams and ewes that would serve your stud’s genetic criteria best.
Donor rams must be highly fertile and produce semen of very good quality.
Donor- as well as recipient ewes may not be pregnant.
Treat all animals with a broad spectrum parasite medication as well as a multivitamin five weeks prior to insemination.
These techniques provide valuable opportunities for the modern sheep stud breeder and it can be applied in practice with success.
Multiple ovulation and embryo transfer are not a swift solution that would lead to the best stud in the country. Though, for the breeders that have a vision for moving forward and are purpose driven, advanced assisted reproduction techniques can have enormous benefit & profit in store.
Pictured: Dohne Merino Recip ewes with embryo Dorper & White Dorper lambs at foot.