X-Message-Number: 9691
Date: Mon, 11 May 1998 07:47:18 -0700 (PDT)
From: Doug Skrecky <>
Subject: Frozen Little Piggies

From the March 28,1998 issue of New Scientist
  Kurt Kleiner, Washington, DC

   Pig embryos can now be chilled and stored, and then succesfully
implanted into sows. Farmers have been using a similar technique with
cattle for moe than a decade, but until now it has not worked well with
pigs. Five piglets due to be born this week at the US Department of
Agriculture research centre in Beltsville, Maryland, will be the third
litter from the technique.
   Cattle embryos have been frozen routinely since the mid-1980s. Breeders
can store thousands of frozen embryos for years and ship them quickly and
cheaply to farmers, who can implant them into their own cows.
   But the same method could not be used in pigs, says John Dobrinsky, the
animal physiologist at the USDA Agricultural Research Service who perfected
the new technique.
   When cow embryos are frozen, they are cooled relatively slowly. The slow
cooling allows ice crystals to form in and around the embryos, which kills
15 to 20 per cent of the cells. While most cow embryos are hardy enough to
be viable after this damage, pig embryos are not.
   So Dobrinsky tried cooling the embryos much more quickly, in a process
called vitrification. He plunged them into liquid nitrogen, chilling them
to -196 C. The cooling is so  quick that ice crystals do not have a chance
to form in the embryo or the liquid surrounding it, so there should not be
any damage to the cells.
   But even after this quick cooling, most of the embryos Dobrinsky
preserved were not viable once they had been thawed. Examining the cells
under the microscope, he eventually discovered that vitrification was
damaging structures called microfilaments that support the membrane of the
cell. These microfilaments help the cell to keep its shape. After they have
been damaged by vitrification, the microfilaments can no linger support the
cell, so when the embryos are thawed out they become deformed and are
unable to function.
   Dobrinsky's solution was to apply a chemical called cytochalasin before
freezing the embryos. Cytochalasin depolymerises the microfilaments,
essentially breaking down their protein structure in an orderly way into
simpler components. These compnents are not damaged by vitrification - and
when they thaw out. the components of the microfilaments re-form into their
correct shape and are able to support the cell.
   Dobrinsky says his laboratory's success rate is 80 per cent, which is
high enough to make the technique commercially viable for pig farmers.
"This technology will allow us to import and export valuable breeding
stock... without the worry of shipping live animals," Dobrinsky says.
   Maurice Boland, an embryologist and head of the animal science and
production department at University College Dublin, says Dobrinsky's method
will finally allow the pig industry to use supercooled embryos in the way
the cattle industry does.
   "This is significant because this is a very difficult procedure in pigs.
People have not been successful before. He's working with one of the most
difficult domestic animals," says Bolland.

Additional comment:
   It looks like where there's a potential cashflow there's a way.....

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