Embryo Transfer Flashcards
What is the principle of embryo transfer?
Transfer of an embryo, derived from the mating of genetically proven, valuable parents, into a fertile but less valuable recipient (host) female who carries the pregnancy to term & offspring to weaning
True or false:
Neither AI or ET are permitted in thoroughbred horses
True
What are the steps in embryo transfer?
- Selection of genetically superior male and female donors
- Superovulation of donor female (not horse)
- Insemination of donor female with semen
- Recovery and identification of viable embryo(s) from donor female
- Synchronisation of recipients with donor female
- Transfer of embryos into synchronised recipient(s)
What are the advantages of embryo transfer?
To maximise reproductive efficiency of high quality animals, especially females which normally produce only 1/2 offspring per annum e.g. cows, mares, ewes
To speed up the genetic improvement of a breed
Circumvents female infertility due to uterine / tract abnormality (providing it’s not genetic)
Enables breeding from injured / aged females (eg broken pelvis)
To enable athletic females to remain “working” e.g. showjumping mare
Lowers risk of disease spread by moving live animals Recipients’ offspring acquire colostral immunity against indigenous pathogens
Role in conservation of endangered species (reliant on availability of recipients)
What are the disadvantages of embryo transfer?
Expensive (cow: £500, mare: ~£1500)
Potential narrowing of gene pool
Enhancement of genetically linked, undesirable traits by mistake (eg lameness in dairy cows)
Requires breed society permission
Technically complex and needs a skilled person
We need to synch the donor and recipient cycles:
If the recipient is a few days behind the donor’s cycle this is…
If recipient is at same stage as donor…
If recipient is in advance of donor…
The recipient is a few days behind the donor’s cycle is ideal and means embryo is transferred into a similar uterine environment this gives the embryo time to “settle in” and release its maternal recognition of pregnancy signal (prevents lysis of CL)
If recipient is at same stage as donor, OK
If recipient is in advance of donor this is not ideal and the uterus may be starting to release PGF2a to lyse CL
How can we synchronise the donor and recipient cycles with progesterone?
Progesterone administration:
mimicks dioestrus, suppresses gonadotrophin release
Via intramuscular injections/ subcutaneous implants/ vaginal sponges (progesterone releasing intrauterine devices PRIDs) or dietary supplement e.g. regumate (mares & sows)
Progesterone withdrawal
Mimicks lysis of CL and decline of progesterone Gonadotrophins released, leading to follicular development
Withdrawal in recipients happens a few days behind donor so results in the recipient cycle being a few days behind the donor’
How can we use prostaglandin F2A to sync the donor and recipient?
Prostaglandin F2a (intramuscular) lyses an existing corpus luteum Prostaglandin F2a (im) of donor then prostaglandin F2a (im) of recipient a few days later So recipient’s stage of cycle is ~24h behind donor Reliant on knowing where the animals are in their cycle ie close monitoring
What is superovulation?
Natural ovulation usually results in the ovulation of one or two oocytes
Superovulation results in the stimulation (FSH) & ovulation of multiple oocytes, in the cow it’s a common procedure but in the horse it’s not currently possible
How do we induce superovulation?
D0 = first day of oestrus
D9-14 administer gonadotrophin (coincides with 2nd follicular wave)
48-72 hours later, administer prostaglandin. Mid cycle CL regresses
40-56 hours later, in oestrus
Inseminate at least twice, 12-18 hours apart
What gonadotrophins can we use in cows for superovulation?
- Equine chorionic gonadotrophin (eCG) or pregnant mare serum gonadotrophin (PMSG)
Contains LH & FSH biological activity
Longer half life in cow - Pituitary follicle stimulating hormone (FSH) from horses/pigs/sheep
What are the limitations of using gonadotrophin to cause super ovulation?
LH activity in eCG & crude FSH preparations can lead to:
premature maturation of oocytes
ovulation of existing follicles (young CL resistant to PGF2a)
deficiency in sperm transport
compromise in embryo transport
However Improved purity of FSH preparations will assist
When should you AI the donor?
Just before ovulation
The embryo will travel down the uterine horn via ……………. at around day ….. post ovulation.
uterotubal junction
4
What day should you do a trans cervical flush?
day 6-8
