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Alta Embryo Group Ltd. first started our research into embryo
sexing in 1989. By 1992, a commercial procedure was being
offered to our clients. This was a major advance in particular
for the dairy industry, where bull calves are wanted only
from the very top end of the breed.
The major difference between a male and a female embryo
is that the cells of the male contain an X and a Y chromosome,
whereas the female cells contain two X chromosomes. The
secret to determining sex then becomes the ability to determine
if a Y chromosome is present.
Researchers in the Department of Medical Biochemistry of
the University of Calgary, working in conjunction with Alta
Embryo Group, were able to isolate a specific sequence of
chemicals found only on the Y chromosome. Through a procedure
called the polymerase chain reaction, the DNA of embryonic
cells can be analyzed for the presence of this sequence.
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When present, it can be multiplied
over a million times. Once this replication has been completed
a simple test indicates whether the male DNA is present.
The procedure involves removing a few cells (biopsy)
from the early embryo. These cells are analyzed and whatever
their sex, the remaining embryo must be the same. Typically,
a donor is brought to Alta Embryo Group early in the morning
(9:00 AM) and the sexes of the embryos are known by 3:00 PM,
when the transfers are done. Biopsied embryos can also be
frozen.
Until June 1992, the sexing procedure was carried out at the
University of Calgary, but at that time the laboratory was
moved to Alta Embryo Group, where the complete procedure is
now carried out. The initial commercialization started in
September 1992. The fee to sex an embryo is saved in transfer
costs alone, since only half the number of transfers will
be performed where calves of a specific sex are wanted.
Results to date have been very encouraging. The sex is
identified more than 90% of the time. There are instances
where the sex is not determined (<10%). Through the use
of fetal sexing by ultrasound, the reliability of this test
for sexing embryos has been confirmed. The right sex is
assigned to an embryo about 95% of the time.
Pregnancy rates following biopsy of embryos are reasonable.
With transfer of fresh sexed embryos, the pregnancy rates
exceed 60%. If embryos are frozen after biopsy, the pregnancy
rate is about 50% following transfer. Combined with direct
transfer, producers can now transfer sexed embryos into
their own recipients.
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