Production of embryos in the laboratory (IVEP), and the
Transfer of the embryos
1. Ovum collection (OPU)
OPU done by harvesting oocytes (ova) directly from the ovaries. A long thin needle is passed through the vaginal wall under ultrasound guidance and the follicles (in which the oocytes develop before ovulation) on the outer edge of the ovaries are aspirated under vacuum. The oocytes are then selected and immediately placed in a transportable incubator in special maturating medium to reach the laboratory within 20 hours.
2. Productionof embryos in the laboratory
This process takes place in incubators that “imitate” the uterus and is divided into 5 steps:
Maturation (ripening) of the oocytes
Fertilization of the oocytes
Cultivation of the embryos
Nutrition of the embryos
Evaluation of the embryos
Embryos that have been successfully grown are then transferred to recipient animals or they can be frozen. The latest technique of freezing IVP embryos (In Vitro Produced embryos) differs from the previously used vitrification process. Embryos are now thawed using the direct thawing technique resulting in improved results.
3. Transfer of the embryos
Transfer of the fresh embryos takes place 8 days after ova harvesting or 7 days after fertilization. This transfer process is identical to the conventional embryo transfer process. The improved direct thaw technique is used when frozen embryos are transferred.
Prior to the transfer, the recipient animal is examined by a veterinarian to determine if she is fit to receive an embryo. The transfer of embryos involves the loading of an embryo into a 0.25 ml straw that is placed in an embryo pistolette. The vaginal area is cleaned and the pistolette is carefully manipulated through the cervix, passed down the selected uterine horn and the embryo is deposited in the last third of the uterine horn. It is important not to damage the inner wall of the uterus, as this will drastically affect the chances of a successful pregnancy. Throughout the embryo transfer process, the recipient is under epidural anaesthetic.
Benefits of IVEP (not over the conventional method):
Better utilization of the genetic potential of top breeding animals – new herds can be built up from the best breeding animals without disturbing the inter calving period of the recipient herd or donor cows;
No hormone treatment is applied;
Donor cows do not undergo conformational changes, such as overdeveloped humps and prominent tail settings;
Collection of oocytes can start as early as 6 weeks after calving;
Oocytes can be collected up to the 3.5 months gestation stage of the donor without affecting the fetus;
Oocyte collection can be performed bi-weekly;
More calves can be obtained during a cow’s lifetime;
More effective use of bull semen – one straw can fertilize 200 oocytes of up to 6 donors;
Older cows with proven records can be used as donors;
Simplified management of the recipient herd;
High conception rates with frozen embryos (55 to 75%).