SUPEROVULATION OF EMBRYO
DONORS
Donor animals are super ovulated using a series of FSH hormone injections.
Not all animals respond the same. In fact, variation to superovulation is one of the largest
and most frustrating problems in embryo transfer programs in all species. The typical response
is 6 to10 ovulations. But this response ranges from none to over 20. Owners must understand
and accept the uncertainty associated with this part of the embryo program. Donors should not
be overly fat, in good health and correctly vaccinated.
EMBRYO COLLECTION
Embryos are usually collected from the donor 6-7 days after breeding. At
Bosque Valley Reproduction Center, embryo collection is performed utilizing a non-surgical
procedure. This technique minimizes surgical complications and allows for a more rapid
recovery of the donor female.
The recovered flush fluid is examined under a microscope, and good embryos are
separate from unfertilized eggs and degenerating embryos. A quality grade (1 being excellent
and 4 being degenerated or unfertilized) and developmental stage is assigned to each of the
recovered embryos. In most cases, excellent quality embryos result in the highest pregnancy
rates. Lower grade embryos (grade 3) may be transferred fresh but not frozen and can result in
a satisfactory pregnancy rate.
EMBRYO TRANSFER
The graded embryos are transferred into the uterus of the recipient female
whose estrous cycle has been synchronized with the donor. Usually two embryos are transferred
into each recipient but singles are sometimes transferred. The quality of the recipient is
probably one of the most crucial factors in the success of an embryo program. Bosque Valley
Reproduction Center has been putting recipients together for clients for the past 13
years.
EMBRYO FREEZING
The purpose of freezing embryos is to hold the embryo in a state of
suspended animation to be transferred at a later date. Grade 1 and 2 embryos can be frozen and
stored in liquid nitrogen for an indefinite period of time. The frozen embryos can then be
thawed and transferred with only a slight reduction in the pregnancy rate normally expected
with fresh embryos. Reasons for freezing embryos can be: 1. Because not enough recipients are
available at the time of embryo recovery. 2. Because the owner wants to target a specific
kidding time. 3. Frozen embryos can be marketed.
WHAT FACTORS AFFECT THE RESULTS OF AN ET
PROGRAM?
Results from ET programs vary greatly. Some programs are complete failures
while others result in success beyond that expected. Most fall within the ranges and averages
described. Failure of superovulation and failure of fertilization are the two reasons most
programs fall below expectations. About 25% of donors fail to respond to superovulation. Some
of those will again fail to respond when repeated. Others will respond normally. This high
variability in results also occurs in cattle ET programs and is a priority for many research
programs
FACTORS AFFECTING SUCCESS
Donor age: As with normal breeding, more ovulations are
produced during the peak years of reproduction – typically 2 to 5 years. Younger or older
donors generally produce slightly fewer embryos.
Season: Results are better during the breeding season in the months of
August to late February. We are however currently having success flushing in the off season
of March to July.
Stress: All goat farmers should know that stress reduces fertility.
Stress will reduce the success of an ET program as well. The times most seriously affected
by stress are at breeding of the donors, the care and preparing of the recipients, the time
of estrus in the recipients, and the first two weeks following the ET in the recipients.
Moving donors for breeding is not recommended. Moving donors for ET is not affected by
stress - as the pregnancy is already established and the eggs are to be removed. Moving
goat recipients may reduce pregnancy rates.
Body condition: Donors in particular should be in good body condition –
ideally not to fat. Recipients must also be in good condition. Donors and recipients should
be started on a plane of nutrition to allow a slight increase in body condition beginning
two weeks prior to insertion of intra-vaginal devices. Salt and access to minerals should be
provided.
Diet: Well-conditioned animals do not benefit from nutritional flushing.
Poorly conditioned animals will benefit. Flushing should focus on energy not protein. Very
high protein diets are associated with reduced embryo quality and increased early embryonic
death in recipients. Diets high in legume might also contain phytoestrogens (plant
estrogens) that are also associated with reduced fertilization and increased embryonic
death. Selecting well-conditioned animals, in good health and on a sensible diet of good
quality forage with a suitable grain supplement and adequate mineral is best.
Donor health: ET can be used to salvage genetics from donors affected by
disease. Results suffer as body condition declines. Serious illness drastically reduces
superovulation results.
Breeding program: Normally we recommend one buck to one or two
superovulated donors.
Recipient quality: The quality of the recipient animals is one of the most
crucial factors affecting success. Healthy recipients that have had at least one set of
kids are best.
Heat detection: Detecting estrus in the donor and recipient animals and
correctly recording this time is critical to the success of an ET program. Teaser animals
play an important role in heat detection.
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