Division of Agricultural Sciences and Natural Resources Oklahoma State UniversityANSI-3158 [625535]

Division of Agricultural Sciences and Natural Resources • Oklahoma State UniversityANSI-3158
Embryo Transfer in Cattle
Glenn Selk
Extension Animal Reproduction Specialist
History of Embryo Transfer
Embryo transfer in cattle has recently gained considerable
popularity with seedstock dairy and beef producers. Most of
the applicable embryo transfer technology was developed in
the 1970s and 1980s; however, the history of the concept goes
back much farther. Embryo transfer was first performed and
recorded by Walter Heape in 1890. He transferred two Angora
rabbit embryos into a gestating Belgian doe. She went on to
produce a mixed litter of Belgian and Angora bunnies. Embryo
transfer in food animals began in the 1930s with sheep and
goats, but it was not until the 1950s that successful embryo
transfers were reported in cattle and pigs by Jim Rowson at
Cambridge, England.
The first commercial embryo transfers in this country were
done in the early 1970s. Initially, embryos were recovered
from valuable donors and transferred to recipient animals using
surgical procedures. It was not until non-surgical methods
were developed in the late 1970s, that embryo transfer grew
in popularity.
Why Consider Embryo Transfer in Cattle?
The reproductive potential of each normal newborn
calf is enormous. There are an estimated 150,000 potential
“eggs” or ova in the female and countless billions of sperm
produced by each male. By natural breeding, only a fraction
of the reproductive potential of an outstanding individual could
be realized. The average herd bull will sire 15 to 50 calves
per year and the average cow will have one calf per year.
With artificial insemination, it is possible to exploit the vast
numbers of sperm produced by a genetically superior bull,
however the reproductive potential of the female has been
largely unutilized. She will produce an average of eight to
10 calves in her entire lifetime under normal management
programs. Like artificial insemination has done for the bull,
embryo transfer is a technique that can greatly increase the
number of offspring that a genetically important cow can
produce.
How is Embryo Transfer Performed on
Cattle?
Virtually all commercial embryo transfer done today uses
nonsurgical recovery of the embryos rather than surgical tech –
niques. The process involves several steps and considerable
time as well as variable expense.1) Selection of the donor cow
The first step is the selection of the donor cow. Beef
producers will differ in their opinions regarding the criteria for
selecting a genetically outstanding cow. Whether the criteria
be performance records, show ring appeal, or both, consid –
eration must be given to potential dollar value of her calves.
As we will see later, considerable expense can be incurred in
achieving a successfully transferred pregnancy. Therefore,
the sale value of the newborn calf should be high enough to
warrant the added expense of this procedure. Because dairy
cattle are selected more routinely on one major trait (milk
production), the decisions concerning donor cows are actu –
ally somewhat less complicated than in beef cattle. However
the economic considerations are equally important. Embryo
transfer is not a “cure-all.” It does not make average cattle
good or good cattle better. It is suitable for a limited number
of seedstock producers with beef or dairy cattle that can be
breed or species “improvers” for one or more economically
important traits.
The potential donor cow should be reproductively sound
to produce maximal results. This means that she should have
a normal reproductive tract on rectal palpation and have a
normal postpartum history, especially with regard to cycle
lengths of 18 to 24 days. Both beef and dairy cows should
be at least 60 days postpartum before the transfer procedure
begins. It has been suggested that prospective donor cows
in embryo transfer programs be selected on the following
criteria:
• Regular heat cycles commencing at a young age.
• A history of no more than two breedings per concep –
tion.
• Previous calves having been born at approximately 365-
day intervals.
• No parturition difficulties or reproductive irregularities.
• No conformational or detectable genetic defects.
She should be maintained at the level of nutrition appropriate
for her size and level of milk production. Both the very obese
cow and the thin cow will have reduced fertility, so it is important
that the donor cow be in an appropriate body condition score
at the time of embryo transfer. (See OSU Extension Circular
E-869 to learn appropriate body condition for beef cattle and
OSU Extension Leaflet L-221 for dairy cattle.) Oklahoma Cooperative Extension Fact Sheets
are also available on our website at:
http://osufacts.okstate.edu
Oklahoma Cooperative Extension Service

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Figure 1. Diagram of the embryo flushing and recovery
procedure.) Superovulation of the donor cow
“Superovulation” of the cow is the next step in the embryo
transfer process. Superovulation is the release of multiple
eggs at a single estrus. Cows or heifers properly treated
can release as many as 10 or more viable egg cells at one
estrus. Approximately 85% of all normal fertile donors will
respond to superovulation treatment with an average of five
transferable embryos. Some cows are repeatedly treated at
60-day intervals with a slight decrease in embryo numbers
over time. The basic principle of superovulation is to stimulate
extensive follicular development through the use of a hormone
preparation, which is given intramuscularly or subcutaneously,
with follicle stimulating hormone (FSH) activity. Commercially
available preparations of FSH are injected twice daily for four
days at the middle or near the end of a normal estrous cycle,
while a functional corpus luteum (CL) is on the ovary. A pros –
taglandin injection is given on the third day of the treatment
schedule which will cause CL regression and a heat or estrus
to occur approximately 48 to 60 hours later.
3) Insemination of the cow
Because of the release of many ova from the multiple
follicles on the ovary, there is a greater than normal need to
be certain that viable sperm cells reach the oviducts of the
superovulated females. Therefore, many embryo transfer
technicians will choose to inseminate the cow several times
during and after estrus. One scheme that has been used
successfully is to inseminate the superovulated cow at 12,
24, and 36 hours after the onset of standing heat. Using high
quality semen with a high percentage of normal, motile cells
is a very critical step in any embryo transfer program. The
correct site for semen placement is in the body of the uterus.
This is a small target (1/2 to 1 inch) that is just in front of the
cervix. There seems to be a tendency for inseminators to
pass the rod too deep and deposit the semen into one of the
uterine horns, thereby reducing fertility if ovulations are taking
place at the opposite ovary.
4) Flushing the embryos
To collect the embryos nonsurgically, a small synthetic
rubber catheter is inserted through the cervix of the donor cow,
and a special medium is flushed into and out of the uterus to
harvest the embryos seven or eight days after estrus. This
collection procedure is relatively simple and can be completed
in 30 minutes or less without harm to the cow. A presterilized
stylet is placed in the lumen of the catheter to offer rigidity for
passage through the cervix into the body of the uterus. When
the tip of the catheter is in the body of the uterus, the cuff is
slowly filled with approximately 2 ml of normal saline. The
catheter is then gently pulled so that the cuff is seated into
the internal os of the cervix. Additional saline is then added
to the cuff to completely seal the internal os of the cervix. A
Y-connector with inflow and outflow tubes is attached to the
catheter. A pair of forceps is attached to each tube to regu –
late the flow of flushing fluid. The fluid is sequentially added
and removed by gravity. The fluid in the uterus is agitated
rectally, especially in the upper one-third of the uterine horn.
The uterus is finally filled with medium to about the size of a
40 day pregnancy. One liter of fluid is used per donor. Many
operators use a smaller volume and flush one uterine horn at a
time. Each uterine horn is filled and emptied five to ten times with 30 to 200 ml of fluid each time, according to size of the
uterus. The embryos are flushed out with this fluid into a large
graduated cylinder. After about 30 minutes, embryos settle
and can be located under a stereomicroscope by searching
through an aliquot from the bottom of the cylinder.
5) Evaluation of the embryos
As the individual embryos are located using the micro –
scope, they are evaluated for their quality and classified
numerically as to the potential likelihood of success if trans –
ferred to a recipient female. The major criteria for evaluation
include:
• Regularity of shape of the embryo
• Compactness of the blastomeres (the dividing cells within
the boundaries of the embryo)
• Variation in cell size
• Color and texture of the cytoplasm (the fluid within the
cell wall)
• Overall diameter of the embryo
• Presence of extruded cells
• Regularity of the zona pellucida (the protective layer of
protein and polysaccharides around the single celled
embryo)
• Presence of vesicles (small bubble-like structures in the
cytoplasm)
Embryos are classified according to these subjective criteria
as:
Grade 1: Excellent or Good
Grade 2: Fair
Grade 3: Poor
Grade 4: Dead or degenerating

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Figure . Cattle embryos at various stages of develop –
ment.Embryos also are evaluated for their stage of development
without regard to quality. These stages are also numbered:
Stage 1: Unfertilized
Stage 2: 2 to 12 cell
Stage 3: Early morula
Stage 4: Morula
Stage 5: Early Blastocyst
Stage 6: Blastocyst
Stage 7: Expanded Blastocyst
Stage 8: Hatched Blastocyst
Stage 9: Expanding Hatched Blastocyst
There is apparently no difference in pregnancy rates of fertil –
ized cells in different stages of development assuming that
they are transferred to the recipient female in the appropriate
stage of the estrous cycle. Stage 4, 5, and 6 embryos endure
the freezing and thawing procedures with the greatest viability.
Embryo quality is also of utmost importance in the survival of
the freezing and thawing stress. Grade 1 embryos generally
are considered the only ones to freeze. Grade 2 embryos
can be frozen and thawed, yet pregnancy rates typically are
reduced. In a Louisiana study involving 1,116 beef and dairy
cows of 15 breeds, 58% of all embryos were transferable, 31%
were unfertilized, and 11 % were degenerated.
6) Selection and preparation of recipient females
Proper recipient herd management is critical to embryo
transfer success. Cows that are reproductively sound, that
exhibit calving ease, and that have good milking and mother –
ing ability are recipient prospects. They must be on a proper
plane of nutrition (body condition score 6 for beef cows and
dairy body condition score 3 to 4 for dairy breed recipients.)
These cows also must be on a sound herd health program.
A tough question to answer is: “How many recipient cows
are necessary?” To establish an average figure for the number
of embryo transfer calves from a single donor cow in a year is
difficult. Variations in conditions are wide, but if a cow is flushed
every 90 days over a 12 month period and five pregnancies
are obtained per collection, an average of 20 pregnancies per
year could result. Some cows have produced more than 50
pregnancies per year by embryo transfer and probably could
have produced more if it had economically feasible. In the
Louisiana study previously mentioned, the average number
of embryos found per cow was 7.4. With only 58% of these
being transferable, the average was 4.3 transferable embryos
per flush.
To maximize embryo survival in the recipient female fol –
lowing transfer, conditions in the recipient reproductive tract
should closely resemble those in the donor. This requires
synchronization of the estrus cycles between the donor and
the recipients, optimally within one day of each other. Syn –
chronization of the recipients can be done in a similar manner
and at the same working time as the donor cows. Injectable
prostaglandin products are available from veterinarians and
should be injected into the recipient at the same time they are
injected into the donor cow. This optimizes the probability that
the recipient will be in the same stage of the estrus cycle as
the donor when transfer takes place. The “Syncro-Mate-B”
system, which involves injecting the recipients and implanting
them with a synthetic progesterone, also has been used suc –
cessfully. The implant is removed nine days after its insertion, and the cows will show standing estrus approximately 30 to 40
hours later. This timing again must match the time of insemi –
nation of the donor cow so that the donor and the recipients
have a similar uterine environment seven days later when the
transfer takes place. Synchronizing drugs only are effective
on recipient females that are already cycling. “Anestrus,” or
non-cycling, cows that are too thin or too short in postpartum
days will not make useful recipients.
7) Transfer of the embryos
The transfer of the embryo into the recipient cow first
requires “loading” of the embryo into a 1/4-ml insemination
straw. This is done under microscopic viewing, with the aid
of a 1-ml syringe and requires considerable practice, pa –
tience, and dexterity. Degenerated or embryos of very low
grade need not be loaded and can be discarded. Just prior
to embryo transfer, the ovaries of the recipient are palpated
rectally to determine which ovary has ovulated. With the aid
of an assistant to hold open the vulva of the recipient cow, the
transfer gun or insemination rod is carefully passed through the
cervix. The tip of the rod is then allowed to slide into the horn
on the same side of the ovary with an active corpus luteum.
The embryo is gently expelled in the forward tip of that uterine
horn. Great care is taken to not cause damage to the lining
of the uterus. Such inflammation and scarring would greatly

ANSI-3158-4Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans
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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Samuel E. Curl, Director of Cooperative Exten –
sion Service, Oklahoma State University, Stillwater, Oklahoma. This publication is printed and issued by Oklahoma State University as authorized by the Dean of the Division of Agricultural
Sciences and Natural Resources and has been prepared and distributed at a cost of 20 cents per copy. 0902reduce the probability of the pregnancy being established.
Embryo flushing and embryo transfer are both done after an
epidural anesthetic has been given to block contractions of
the digestive tract and aid in the ease of manipulation of the
cervix and the uterine horns. Embryos can be transferred
immediately upon recovery and evaluation or may be stored
frozen in liquid nitrogen and transferred at a later date. The
freezing and thawing process also is also very intricate and
usually results in an approximate 10 – 20% reduction in preg –
nancy rates from those observed with fresh embryos.
Frozen embryos are a marketable commodity and have
been especially useful in international sales of United States
beef and dairy genetics. Producers in this country who believe
that they own cattle with the genetic capability to be valuable
in other nations may wish to contact their State Department
of Agriculture and ask about regulations and marketability of
frozen embryos from their herd. Different nations have differ –
ent health requirements of cattle producing frozen embryos
for import into their country. Therefore, individual inquiries
are necessary to learn what health and legal requirements
are expected.
Costs of Embryo Transfer
The costs of embryo transfer are as variable as the costs of
buying a new automobile. Many different options and packages are offered by embryo transfer technicians. Some technicians
perform embryo transfer only on the farm or ranch where the
donor cow is located. Others have facilities to house and
board donor and recipient cows and perform embryo transfer
under hospital-like conditions. Many technicians have the
equipment and expertise to freeze and store embryos for
later transplantation or shipment to other countries.
Minimum costs of $250 per pregnancy have been reported
by embryo transfer technicians. These costs may not include
drug costs for superovulation, and certainly do not include
semen, registration, embryo transfer certificates, blood typing
of donor cows and ancestors, and most importantly the cost
of maintaining the donor cow until the calf is weaned. Three
to five straws of valuable semen can be priced from $45 to
$300. Proper nutrition, health care, and synchronization of
the donor and the recipient can add another $400 to $500
expense to each successful pregnancy. Consequently, many
purebred operations conducting embryo transfer on a regular
basis consider that each “ET” calf must have a market value
of $1500 to $2000 greater than other naturally conceived and
reared calves in the herd before embryo transfer is consid –
ered.
Beef and dairy producers considering using embryo
transfer should first visit with their breed representative to
determine the specific requirements need for certification
and registration of embryo transfer calves in that breed.