Use of sexed semen is now a reality
for many cattle breeders. The early research on this technology
was done by USDA more than 15 years ago. The first sex-selected
calf using frozen sexed semen and AI was born in 1999. In 2004
this process became commercially available through a company
called Sexing Technologies with labs in Texas, Ohio, Wisconsin and
Brazil.
Gustavo Toro, Marketing Director for GRI (Genetic Resources
International) and sister company Sexing Technologies, says that
the research was done by Dr. Larry Johnson from Colorado State
University, in conjunction with a grant from the USDA. Johnson
developed a method for staining sperm, to facilitate sorting, and
worked closely with Mike Evans (Sexing Technologies) to develop
the instruments needed.
“When the technology was developed and a patent issued, a company
called XY Inc. of Fort Collins, Colorado, bought the patent. Our
company, Sexing Technologies, has a license for the U.S. and a few
other countries. We are the largest company dealing with sexed
semen. Our headquarters in Navasota, Texas is where we do all the
research and training. We also produce sexed semen for individual
customers as well as the big AI centers,” says Toro.
“We have a second lab in Brazil.
In March, 2006 we opened a lab in Ohio with Select Sires. In
August of 2006 we opened a lab with ABS in Wisconsin. In May 2007
we opened one in Holland. We’ve also signed a contract with Genex
and AltaGenetics and we have their bulls here in Texas where we
are collecting for them. So we are now lined up with the 5 biggest
AI studs in the world. We have our labs and machines in their
facilities,” says Toro.
In Texas some of the private
customers include producers of rodeo stock, like Vernon Guidry and
Bucks by Design. “We have done several of the bucking bulls, and I
think this will become a very important tool in that industry. It
is growing rapidly,” he says. Use of sexed semen in the beef
industry is also starting to catch on. The dairy industry is using
this technology the most, however, because almost all of those
breeders utilize AI. Only 6 percent of the beef cows in this
country are bred by AI, compared with almost 90 percent in the
dairy world, says Toro.
“We have now done sexed semen for
18 different breeds. Interest is increasing daily. We thought we
would just have 4 machines in Texas, but we have 9 running at
present and will soon have 11. Select Sires started with 4 and now
they have 8. ABS started with 4 and we are now installing 4 more
for them; they can’t keep up with demand,” says Toro.
The bulls have to be at one of
these studs in order to have this process done. “The only facility
where we are doing custom work for people is here in Texas. All of
the others are just processing their own bulls. They are not
offering this service to any outside bulls,” he explains.
COST
The cost of processing sexed semen is about $35 to $60 per straw,
depending on the quantity being done. Dr. Bob Everett at Cornell
University did a study to show the economic return to producers
using sexed semen. In several instances, having a calf of the
desired sex from a certain cow/bull combination will more than pay
for the cost, and may even return several hundred dollars on that
investment.
THE TECHNOLOGY
“The way the process is done is based on the fact that the x
chromosome has 3.8 percent more DNA than the y. The machines can
read that difference in DNA content,” says Toro. The semen is
stained with a fluorescent dye and then passed through a machine
(flow cytometer) that can sort the sperm as it goes by in a stream
of single droplets. The female producing sperm with the x
chromosome shines brighter than the y because the x chromosomes
are 3.8 percent larger and have absorbed more dye. A laser in the
sorting machine determines the gender of the sperm based on the
amount of light it emits.
In developing this technology, Dr.
Johnson modified existing flow cytometers to accomodate analysis
of stained sperm. Flow cytometry is the measurement of cells as
they flow by a detector. The flow cytometer uses focused laser
light to illuminate cells as they pass by the laser beam one at a
time in a fluid stream, traveling 60 miles per hour; more than
4000 sperm per second are sorted and processed. This seems fast,
but it takes about 3 to 4 times longer to process sexed semen than
to process conventional semen for shipping or freezing.
The X-bearing sperm are sorted off
in one direction, the Y- bearing sperm in another, and anything of
undetermined sex passes straight through as waste. The sorted
sperm are then frozen in .25 cc straws to be used for AI. An
ejaculate yields fewer straws of sexed semen than conventional
semen.
One advantage to the sorting
process (which also helps make the sexed semen more successful in
low dosage than regular sperm) is that damaged or dead sperm are
sorted off. A normal ejaculate always has a certain amount of
dead, dying or damaged sperm cells, so when it’s sorted by the
sexing process, these are eliminated—making the remaining sperm
more viable.
The highly purified groups of
sorted semen are then frozen for future use in AI, to enhance AI
programs or embryo transfer. For many years the drawback in using
sexed semen was the difficulty in getting enough sorted sperm from
an ejaculate to make it practical. Studies at Colorado State
University helped make it feasible. Their theory was that since it
only takes one sperm to fertilize an egg, why use 20 million (the
recommended amount for optimum reproduction)? They began
experimenting with low dose insemination for AI, and it
worked—especially if the cow was at the optimum point in her heat
period.
Today, advanced reproductive
techniques like in vitro fertilization (where the egg is
fertilized in the lab and then used in embryo transfer) make sexed
semen even more practical, since only a tiny amount of sperm is
needed for fertilizing a large number of eggs. Sexed semen works
well (with highest success rates) in a well managed AI or ET
program in which timing of insemination is optimum for proper
fertilization of the egg, but probably works best in an IVF
program. Some variability has also been noted with different
bulls; semen from various bulls goes through the sorting machines
differently, so some bulls are better candidates for sexed semen
than others.
BENEFITS OF USING SEXED SEMEN
When using sexed semen, the results are predictable about 93
percent of the time. It can be a handy tool to increase your
heifer numbers or steer numbers. This option is very useful for
the dairy industry, since there is always a market for heifer
calves but not for the bull calves. In the beef industry, it is
handy to be able to select the gender of calves if the producer
wants to keep replacement females from certain cows/bulls, or
wants just steers from a terminal cross.
In any given herd, the option of
sex determination could be useful for reducing calving difficulty
in first calvers (since heifer calves are typically smaller at
birth than bull calves), or for producing a higher number of good
females to choose from as replacements if you are wanting to
expand your herd size without buying outside cattle. If you can
keep a closed herd, not having to depend on bringing in any other
females, you can cut down on some of the health problems that may
be inadvertantly introduced, and in many cases you also have
better knowledge of the genetics in your own herd. If you want
your best cows to all have heifers, this can give you faster
genetic progress in improving your cow herd, enabling you to keep
more good females and cull more deeply.
“A producer may want heifers from
the top 10 to 15 percent of their cows, and steers from the rest
of the herd,” says Toro. When the market is good for replacement
females, breeders may opt for more heifers, and when the market is
better for steers they may choose to produce mostly male calves.
Seedstock producers may have bloodlines they are selecting for
maternal qualities for brood cows and others they are hoping to
use for marketing bulls. This technology gives producers the
choice, and also enables them to develop an early strategy for a
potential future market.
In female sales, for instance,
some breeders are finding their bred cows and heifers worth more
when bred with sexed semen. Bred heifers guaranteed to have heifer
calves (and less calving problems) may bring a premium. Other
buyers may want females that will produce only male calves.
Seedstock producers marketing pen lots of bred females or pairs
may find an advantage in being able to offer cattle guaranteed to
have one sex or the other, or may find a premium in offering
exceptional female bloodlines in a 3-way package—a cow with heifer
calf at side and bred back to have another good heifer calf.
For more information on sexed
semen, contact GRI or Sexing Technologies at 936-870-3960 or
gri@griglobal.com or visit
their website at
www.griglobal.com.
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