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Beef Cattle Embryo Transfer
Embryo Transfer Benefits
Embryo transfer in cattle has become one of the most exciting and progressive
procedures available to today's producers. With conventional production, the
average cow produces six to seven calves in her lifetime.
Embryo transfer can increase her reproduction efficiency to numerous calves per
year, thus increasing your selection opportunities many times. Along with
artificial insemination, embryo transfer offers progressive producers
fascinating genetic opportunities.
Selection of Donors ~
Donor selection should be based on several criteria. Genetic superiority is of
major importance and should be evaluated with the following traits in mind:
birth weight, milking ability, pre-weaning growth, post-weaning growth, and
carcass cutability. Official sire summaries can assist in measuring and
comparing the above traits. Records should be used to evaluate maternal breeding
value, weaning breeding value and yearling breeding value.
All of these values are objective measurements based on pounds of gain as
measured on a scale. Ultimately, value of progeny must justify an embryo
program. Reproductive ability is the second main criteria to determine donor
selection.
To enhance the success of your embryo transfer program, the donor should meet
the following characteristics: 1) two or more years of age, however, heifers can
and have been used successfully in embryo transfer programs, 2)regular calving
each year, 3) conception after one or two services, 4) regular estrous cycles,
and 5) no history of retained placenta, metritis or cystic ovarian disease.
Sire selection is based on the use of well proven bulls that produce high
quality semen. By using reference sire summaries, the producer can evaluate EPDs
for birth weights, weaning weights, yearling weights and milk production to
assist with sire selection.
Pre Transfer Preparations for the Donors
Blood or hair samples should be submitted for typing or DNA analysis
approximately two months prior to flush date if possible. This insures the
results are completed before pregnancies result and that the calves can be
registered.
Materials for taking this sample are available from your breed association.
Other breed requirements must be determined before transfer as well.
The following vaccines should be given within the last six months: IBR/BVD, BRSV,
7 Way Clostridial, 5 Way Lepto, and Ivomec. These vaccines should be given at
least 4 weeks prior to embryo collection and transfer.
Superovulation
Superovulation consists of injecting the donor cow with a fertility drug, FSH
(follicle stimulating hormone), to induce multiple ovulation. Injections begin
on approximately the tenth day after estrus and consist of twice daily
injections of FSH for four days.
On the fourth day of the FSH injections, prostaglandin is also injected to cause
the regression of the corpus luteum. This triggers estrus one and a half to two
days later. The donor is artificially inseminated with one unit of semen at
first observed standing heat.
Twelve hours later, she is bred again using two units. At 24 hours she receives
1 additional unit of semen. Variations to this breeding schedule will be used
depending on the history of the donor, quality of semen used, and cost of semen
Recipients
Recipients should be healthy, of medium to large frame, on a gaining plane of
nutrition and cycling regularly. In addition, they should be vaccinated for
Brucellosis (with an official calfhood vaccination tattoo in the right ear),
Rednose, Virus Diarrhea, BRSV, Parainfluenza 3, 5 Way Lepto and 7 Way
Clostridial vaccine, and Ivomec.
Recipients will be synchronized with prostaglandins to be in estrus the same
time as the donor cow. Those in estrus within 24 hours before or after donor
estrus can be used as recipients.
Since there is no way to predict the number of embryos produced by the donor
cow, a sufficient number of recipients are synchronized to anticipate average
collection. Ten to fifteen recipients per donor is the usual estimate.
When embryos are to be frozen, a few recipients should be prepared to implant
lower grade embryos which are not freezable.
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Collection of Embryos
Non surgical techniques are used to recover embryos seven or eight days after
estrus. The donor is given an epidural block in the area of the tailhead to
prevent straining. The vulvar area is scrubbed to prevent contamination.
A flexible rubber tube called a R?ch catheter is gently threaded through the
cervix and up into the uterine horns. A small rubber balloon cuff is inflated
with fluid to expand and fill the uterine lumen. This prevents any backflow of
fluid. There are several holes near the tip of the catheter that precede the
inflated cuff. Fluid enters the uterus by means of these holes after being
injected through the catheter with a 50 cc syringe.
Once the fluid is in the uterus, the horn is gently massaged and the fluid
(containing the embryos) is drawn back out through the catheter. This process is
then repeated in the other uterine horn. The embryos are collected in a
zwitterionic buffer solution containing antibiotic/antimycotic.
Embryo Searching
The fluid flushed through the uterus is filtered through a special filter that
traps the embryos but allows the fluid to drain free. All but 50 cc is drained
through the filter. This remaining fluid, containing the embryos, is divided
into several scored petri dishes to be searched.
The embryologist searches each dish under a dissecting microscope and upon
finding an embryo, removes it with a pipette to be transferred to a small petri
dish. All the embryos are placed in these small dishes to later be washed,
identified, and classified.
Transfer of Embryos
Non surgical. Embryos to be transferred non surgically are aspirated into 0.25
ml artificial insemination straws. Air bubbles are placed on either side of the
fluid containing the embryo. The straw is fitted into a cassou gun, which is
covered with a plastic breeding sheath. The cassou gun is similar to an A.I. gun
but slightly longer so that it can go deeper into the uterine horn.
The recipient is placed in a squeeze chute and given an epidural. After being
palpated for a corpus luteum, the cassou gun is inserted mid way up the uterine
horn of the recipient and the embryo is deposited in the horn ipsilateral to the
corpus luteum. This technique takes considerable practice to achieve
satisfactory pregnancy rates.
Results
From the average donor, approximately eight to ten embryos are collected.
Several of these may be unfertilized or degenerate. Approximately seven embryos
are of transferable quality and on the average, four or five pregnancies will
result after their transfer.
Approximately 65% of fresh and 60% of frozen embryos result in pregnancies. Your
success rates may vary greatly because every donor is different. Some donors
will consistently produce large numbers of excellent embryos, while others may
only produce a few.
For embryo transfer to be successful, it is essential to pay the strictest
attention to detail, thus minimizing any outside influences on the success of
the transfer. |