Objectives
• Increased output from high quality females – higher genetic gain
• Easier transport of genetic material especially for export
• Short or Long- term storage of genetics
Procedure
The procedure works by using intravaginal sponges and hormone injections to cause ewes to release large numbers of ova or eggs. These eggs are fertilised using artificial insemination and five days later the resulting embryos are collected surgically under general anaesthesia and transferred to surrogate (recipient) ewes or frozen and stored in liquid nitrogen. Collection of the embryos is undertaken with the ewe positioned in a cradle on her back as for AI but it is a slightly more involved procedure and a general anaesthetic is used. You should be aware that as with any surgical procedure there are recognised risks though the incidence is extremely low.
Fertility must be optimal to allow:
• Maximum numbers of follicles to develop
• The maturation and ovulation of the follicles at the right rate
• A suitable environment to be present in the womb for the inseminated sperm cells to survive until the eggs are ready to be fertilised
• Fertilisation
• A good environment in the womb for the developing embryos both for 5 days in the donor and following transfer to the recipient
Schedule of events
• Day 0
Progesterone impregnated sponges are placed intra-vaginally in ewes.
The sponges allow follicles on the ovaries to develop but prevent them from maturing and actually ovulating (releasing eggs). The sponges are inserted for 12 days.
• Days 9-12
For around the last 4 days of this process, hormone injections are given to stimulate lots of follicles to grow.
The result of these two actions is that a greater than usual number of follicles develop on the ovaries. Once developed the follicles are held in a kind of suspended animation.
• Day 12
The last stage is removal of the sponges. This process allows all of the follicles to finish maturing and then to ovulate at the same time, releasing eggs all of a similar age (known as ova) into the fallopian tubes of the ewe.
After a number of hours the eggs are ready for fertilisation by waiting sperm cells and carry on down the fallopian tubes and into the womb.
• Day19 or 20
Fertilised eggs now known as embryos are collected under general anaesthesia (known as flushing) and implanted into surrogate or recipient ewes.