Embryo Transfer

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Embryo Transfer in Cattle

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Introduction

• Embryo Transfer is a expensive procedure, costing
  around 300 for each flush and approximately 270
  for each calf born. Not including the cost of the
  semen.
• Students should understand that ET is a
  complicated procedure with a fairly high
  difficulty level.
• ET should only be performed by trained
  professionals.

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Objectives

• Explain the benefits of embryo transfer.
• The impact that embryo transfer has on the
  livestock industry.

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Reproductive Anatomy
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What is an Embryo?

• An embryo is an egg that has already been
  fertilized by a sperm cell.
• It is an organism in the earliest stage of
  development.

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What is Embryo Transfer?

• ET involves the removal of an embryo from a
  female of superior genetics and the placement of
  the embryo into the reproductive tract of a
  female of average genetics.

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What is the Goal of Embryo
Transfer?

• The goal of ET is to obtain the maximum number of
  genetically superior embryos in a minimum amount
  of time.

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Benefits of Embryo Transfer

• Traditionally, cows produce only one calf per
  year. ET allows the production of many offspring
  within a year from a single cow.

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Benefits (continued)

• ET can increase the genetic potential of a herd
  in a relatively short period of time.
• ET can increase milk production in dairy herds.
• ET can increase weaning weights in beef and dairy
  herds.

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Benefits (continued)

• ET allows other producers to take advantage of
  superior genetics because frozen embryos can be
  shipped almost anywhere.
• ET preserves superior genetics for future
  generations due to embryo freezing.

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The Process of Embryo Transfer

• ET begins with the selection of a donor cow.
• The donor cows will contribute the embryos to be
  transferred.

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Donor Cows Have Superior
Characteristics

• High milking ability
• High growth rate
• Outstanding reproductive capacity

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Recipient Cows

• Finally, recipient cows must be selected.
• Recipient cows serve as surrogate (foster)
  mothers to the calves, but contribute no genetic
  information.
• For this reason, the genetic makeup of the
  recipient cow is not as important as the makeup
  of the donor cow.

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Recipient Cows (continued)

• However, the recipient cow must be able to
  maintain her pregnancy to term and produce an
  adequate milk supply for her calf.

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Synchronizing the Estrous Cycle

• Once the donor and recipient cows have been
  selected, they must be synchronized so they are
  on the same phase of their estrous cycle.
• It is important to synchronize estrous cycles
  because the reproductive environments of the
  donor and recipients must be identical in order
  for the embryo to survive the transfer.

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Synchronizing the Estrous Cycle
(continued)

• The estrous cycle is controlled by the production
  and secretion of hormones at the proper time
  during the cycle.
• Prostaglandin (PGF2a) is the hormone used to
  synchronize the estrous cycles of the donor and
  recipient cows.

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Synchronizing the Estrus Cycle
(continued)

• Prostaglandin is produced naturally by the cow.
  However, a synthetic version called Lutalyse is
  given in one or two injections intra muscular in
  the neck or hip to synchronize estrous cycles.

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Preparing the Donor Cow to be
Flushed

• Before the donor cow is flushed, she is
  superovulated with a series of injections of
  Follicle Stimulating Hormone (FSH).
• Ovulation is the process of releasing eggs.
• Superovulation causes the ovary (the female
  reproductive organ) to produce many follicles.

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Preparing the Donor Cow to be Flushed
(continued)

• Follicles are small blister-like structures that
  develop on the ovary containing one egg each.
• When the follicles ovulate, the eggs are
  released.
• Superovulation ensures that many eggs will be
  released because there are many follicles
  present.

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Breeding the Donor Cow

• When the donor shows signs of estrus (the time
  period during the estrous cycle when she will
  allow breeding), she is ready to be bred.
• Some signs of estrus are riding other cows, clear
  vaginal mucus, and pacing the fence.

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The Flush

• Once the donor cow has been bred, the embryos are
  allowed to grow for six days.
• During this time the embryos also travels down
  the reproductive tract from the oviduct (the site
  of fertilization) to the uterus where they can be
  flushed out.
• On the seventh day, the embryos are ready to be
  removed. This process is called flushing.

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The Flush (continued)

• Embryo professionals use a non-surgical method to
  remove the embryos. The process requires
  experience and a patient, steady hand.

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The Flush (continued)

• An injection of lidocaine is given prior to the
  flush to reduce pressure and stress on the donor
  cow and to make the flush easier for the ET
  professional.

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The Flush (continued)

• To begin the flush, a catheter is passed through
  the cervix into one uterine horn.

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The Flush (continued)

• The catheter contains a balloon that is inflated
  with a saline solution in order to seal the
  entrance to the uterus so fluid and embryos are
  not lost.

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Removing the Embryos

• The uterine horn is filled with flush media and
  massaged to allow the embryos to flow out of the
  tract.
• This process is repeated several times in each
  uterine horn.

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Collecting the Embryos

• Embryos are carried out of the reproductive tract
  through plastic tubes and collected in a filter
  with the flush media.
• The pores in the filter are smaller than the
  embryos so excess fluid drains out of the filter
  without losing the embryos.

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Injecting Penicillin

• After the embryos have been flushed out, uterus
  injected with penicillin to kill any missed
  embryos or infections.

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Embryo Statistics

• An average of 7-10 embryos is collected from each
  flush.
• However, the number of embryos obtained from a
  single flush may range anywhere from 0-60.

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Separating the Embryos

• In the lab, embryos are separated from the flush
  media and examined under a microscope to
  determine their quality and stage of development.
  

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Embryo Size and Quality

• Embryos are microscopic in size (about 0.2 mm).
• Only undamaged embryos at proper maturity should
  be transferred.

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Embryo Quality
The embryos on the left are damaged and should
not be transferred.
The embryo on the right is of proper maturity and
quality and should be transferred.
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Transferring the Embryos

• The embryo to be transferred is put into a small,
  plastic straw and then loaded into an embryo
  transfer gun.

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Transferring the Embryos (continued)

• The embryo is then inserted into either the left
  or right uterine horn depending on which ovary
  has a corpus lutuem (CL).
• The CL is a structure on the ovary that secretes
  the hormone progesterone which is needed to
  maintain the pregnancy.

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Transfer Immediately or Freeze

• Embryos should be transferred as soon as possible
  after the flush (within 8 hours at least).
• Embryos can also be frozen for later implantation
  and stored in liquid nitrogen tanks.

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• Benefits to Embryo Transfer
• -A single heifer or cow is able to produce
  multiple
• calves from the same genetic line.
• -An older superior cow is able to donate ovules
  for
• embryo transfer.
• -Embryos can be frozen and stored for future use.

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FACTS
-In 1987, 3.6 (5,105) of all calves registered
were a result of embryo transfer. -In 2002,
25,093 calves resulting from ET were registered.
This was 8.9 of all calves registered. -In
2007, just under 40,000 calves resulting from ET
were registered. This accounted for about 11.5
of total registrations.
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Disadvantages of ET
-Increased expenses and higher breakeven costs
for calves. Requires a higher level of
management. Increased potential for spread of
certain diseases. Not all potential donors
respond positively to treatment.
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Summary

• ET can be costly, so the return on the investment
  should always be greater than the input costs.
• ET should only be performed using donor cows of
  superior genetics.
• Bull selection should be based on superior
  genetics as well.

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Conclusion

• If the required conditions are met, embryo
  transfer can be a beneficial way to produce
  superior cattle.