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Embryo transfers locally.

GENERAL INFORMATION EMBRYO TERMINOLOGY

The female gamete in mammals is called an egg or ovum.  An oocyte is the term used for a newly ovulated female gamete.  After fertilization, the oocyte becomes a one-cell embryo or zygote.  The embryo then divides into two-cell, four cell, etc. stages.

At the 16-cell stage, the embryo becomes a morula (Latin for mulberry). When a cavity (blastocoele) forms between the cells of the embryo, it is termed a blastocyst.  The first three divisions of the embryo are called cleavage divisions; thus, one-to eight-cell embryos are defined as cleavage stages. During this time the embryo actually decreases in weight. Only at the morula stage does the embryo begin to weigh more than at the one-cell stage.

During the morula stage, cells of embryos change from spherical to polygonal in shape. This phenomenon is termed compaction. During compaction, specialized junctions form between cells, so the cells can communicate with each other.  Compaction is an excellent sign that the embryo is developing normally.
As the morula develops into a blastocyst, it forms a cavity, the blastocoele, by expending energy to pump fluid between the cells. Thus blastocyst formation also is indicative of continued normal embryonic development.


Embryo flushings

EMBRYO TRANSFER IN SHEEP AND GOATS

Multiple ovulation and embryo transfer (MOET) offers several advantages over natural breeding.  One of the biggest advantages is that it allows for multiple offspring in a given year. 

With artificial insemination (AI) emphasis is placed on the use of genetic superior rams to enhance genetic improvement and increase progeny numbers of that ram.  The ewe adds 50% to the genetic make-up of the offspring thus making embryo flushing the most efficient way to use both genetic superior rams and ewes to produce genetic superior offspring and increase progeny numbers of especially the ewe. 

DESCRIPTION OF THE PROCESS

  • Intravaginal 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 5½ to 6 days after insemination surgically, 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.
  • Embryos are collected and kept in special media during the whole process.  With the aid of a stereomicroscope, embryos are picked out off the media and classified as Grade I, Grade II (transferable embryos) and Grade III's that are not viable for transfers.  The embryos go through multiple washings to ensure it is free from debris.
  • 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.  Official protocols to export embryos have been established since 1994 with Canada, Australia and Brazil.  Embryos were also exported by special import permits to other countries. South Africa is free of a number of serious diseases like Scrapie and had a clean record with all exports during the past 10 years.  Overseas breeders interested in Dorper or any other breed of sheep or goats should request their governments to establish a protocol for import from South Africa.
  • Multiplication of numbers of the imported sheep or goat breed.
    Due to limited numbers importers have to use these techniques to multiply their progeny.  Even with limited numbers, only the better performing animals should be flushed.
  • Embryos are regarded as the safest means of transporting genetic material across the globe. Donor animals are tested before and after collection of embryos for all viral and bacterial diseases of concern. Embryos go through an intensive washing system before freezing and are sealed in straws.

LIMITATIONS OF THE M.O.E.T. TECHNIQUES

  • Cost: It is a fairly expensive exercise and only viable for stud breeders.
  • Experience of operators: Only professionals with good experience in this field can perform it.
  • High level of management: Good recordkeeping, management control and feeding are required to make a success of it.
  • Number of flushings: Ewes can be flushed several times but there is a limitation due to the surgical procedure.

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.
  • MOET is not cheap, but current prices of animals in the stud animal arena endorse larger inset costs.

CONCLUSION
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 profit in store.

LOCAL EMBRYO FLUSHING AND EMBRYO TRANSFER PROGRAMS

Carrying out a successful ET program “on farm” with satisfying results is possible; however a very good management system is necessary.

PLANNING
Programs do take time to plan and organize and a minimum planning time of 6-8 weeks is usually necessary or even longer if recipients have to be purchased. During this time, several items have to be attended to - i.e.

  • Nutritional management of donors and recipients
  • Tagging and management of donors and recipients
  • Organize semen/rams – don’t leave this until the last days.
  • Organize a AI technician who should be fully informed of your plans
  • Organize facilities – Under roof facility
  • About 4-5 weeks prior to anticipated operation date, a program of action will be forwarded to you along with appropriate drugs etc.  This program will outline on a day to day basis the course of events designed to achieve a successful result.  This should be studied carefully.

NUTRITION
Nutrition is one of the most important factors that must be considered in reproduction.  Lifelong, good nutrition in sheep accelerates performance, from the earliest stages of conception through to adolescence and beyond.  While it is well known that better feeding just before insemination improves responsiveness of the ovaries.

TAGGING AND MANAGEMENT
Clear and visible ear tags to identify each animal are important for recordkeeping and statistical analysis for future reference.

FACILITIES REQUIRED
Fortunately the techniques employed in carrying out an insemination, flushing and embryo transfer program mean that sophisticated facilities are not required. A simple roof covered area that can form some form of protection from the weather (wind, rain and sun). Once a program is organized the day can’t be changed if the weather is bad, so some accommodation for bad weather is necessary.
The use of electricity is needed to power microscopes and freezing machines.

COLLECTION DAY
Embryo collection is normally carried out 6 days after “insemination”.
The flushing procedure may take 20-30 minutes.

The recovered fluid is searched microscopically and embryos are identified and transferred to special holding fluid. The searching procedure may take some time as embryos are very small and often hard to find amongst the mucous and debris also recovered.   The embryos are recovered and examined, and classified and graded for quality.  Embryos are then either loaded into straws for transfer or are frozen.

RECIPIENTS AND EMBRYO TRANSFER
The correct and appropriate selection and management of the recipient is vital to the success of the embryo transfer program.  Management of recipients from the first day of the program right through until the lambs are born can influence the success of the whole operation. Many a program is rendered less productive by poor or careless recipient care.

Embryos to be transferred are loaded into a straw and identified as to donor, stage and quality.
Appropriate recipients are restrained and examined for suitability. If considered suitable the uterine horn is exposed through a small abdominal incision and embryos are introduced into the uterine lumen of the recipient animal.  The recipient is released.
Pregnancy testing after 6 weeks confirms the pregnancy status of the recipient.
The conception rate of transferred embryos can range from 60-70%.

FREEZING OF EMBRYOS
With special media and apparatus embryos can be frozen and stored in liquid nitrogen.
Average conception rate with frozen embryos are 45-50%.

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