ZITA the supercow was a beast in a million, the highest-ranked Holstein in
the US. In her prime her milk yield was nearly twice the average, and cattle
breeders paid top dollar to get her genes into their herds. Then, alas, she got
old and died.
But dry your eyes. This is the age of the clone, and the genetic blueprints
of prize cows can now be saved from the grave. Grazing on a farm in Maryland are
Zita-2 and Zita-3, two three-month-old calves cloned using two cells from Zita鈥檚
ears.
American cloning companies are busy making multiple copies of just about
every top pedigree cow and bull in the land. In time, they hope identikit
supercows and superbulls will be bred, milked and even butchered for profit,
just like the old ones. 鈥淲e鈥檙e cloning some of the highest-level bulls and think
we can sell hundreds,鈥� says Ron Gillespie of Cyagra, the Massachusetts company
that cloned Zita. For prize breeding animals, which can fetch $40,000 or
more, cloning is economic even at today鈥檚 going rate of $15,000 to
$25,000 per cow. And as more animals are cloned, the cheaper it will get.
鈥淧ush the price down to $10,000 and there would be 100,000 animals that
it would be economic to clone, and in the $5000 range, millions.鈥�
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That鈥檚 millions of cloned cows and bulls. Created just to make food. In the
US alone.
Ever since Dolly the sheep was born, fears about cloning have been tempered
by hopes that the technology will one day save thousands of human lives. And so
it might. Already cloning is enabling scientists to produce animals capable of
secreting valuable drugs in their milk, and to look for ways to clone tissues
for transplantation. But developing these medical spin-offs could take up to 10
years. Cloned beef steaks and milkshakes could be with us much sooner.
So far, it鈥檚 the baby cloners who have been in the firing line. Now, as
companies like Cyagra forge ahead, the prospect of cows being cloned en masse
for food is provoking alarm as well. And not just among animal welfare
campaigners.
Ian Wilmut, the scientist who led the Dolly team, says it is vital that
controlled farm trials of cattle cloning are carried out before any commercial
production of cloned meat and dairy food is allowed. Companies need to prove
that large-scale farm cloning involves no undue animal cruelty, that clones are
as healthy as ordinary animals, and that food from cloned animals and their
offspring is as safe and nutrious as conventional food, Wilmut told New
快猫短视频. The cattle cloners 鈥渙ught to be making systematic comparisons
between clones and animals produced by embryo transfer, looking not just at
their milk yield but also their health and lifespan鈥�. Until then, he says cloned
food ought to be banned from shops and restaurants. 鈥淚f companies start
marketing this food and there are problems it will bring the whole technology
into disrepute.鈥�
Herds of identical cloned animals would be a welfare disaster, says Joyce da
Silva of Compassion in World Farming. 鈥淭here would be a huge loss of genetic
diversity with unforeseeable results in terms of animal illness.鈥�
A more immediate fear is that four years on from Dolly, cloning is still a
waste of animal life. For every Zita-2 or Zita-3, say scientists at the sharp
end, scores of clones die in the womb or develop deformities, and even clones
that look healthy could be 鈥渢icking timebombs鈥� destined to go awry.
Until recently, the full extent of the problem was hidden, largely because
the cloned animals that don鈥檛 survive don鈥檛 get much space in scientific papers.
A rare exception is a 1999 paper that appeared in the journal Theriogenology
(vol 51, p 1451) under the heading 鈥淐linical and pathological
features of cloned transgenic calves and fetuses鈥�. The paper is an
eye-opener.
Take the short life of 鈥渃alf 1鈥�. Its placenta was bloated with six times the
fluid of a normal pregnancy. Yet at birth it appeared normal. It mooed, started
breathing and tried to stand. But appearances were deceptive. Its blood oxygen
levels were one-third of what was expected, and carbon dioxide was up to three
times normal. A day later, oxygen was pumped into its lungs and it was sedated
with valium, but to no avail. The calf was soon dead. Its lungs had never
properly inflated, it had an enlarged heart, and its liver, which should have
been a smooth crimson organ, was a roughened orange slab.
And those, remark some cloners wryly, were the 鈥済ood old days鈥�. 鈥淲e saw
consistent defects, so we thought we鈥檇 find consistent solutions,鈥� says Jim Robl
of the Massachusetts-based company Hematech. Over-sized calves, lung and
heart problems were the major themes. But now the more cloners you talk to, the
longer the list of defects you hear about: enlarged tongues, squashed faces, bad
kidneys, intestinal blockages, immune deficiencies, diabetes and shortened
tendons that twist the young animal鈥檚 feet into useless curves. 鈥淭here鈥檚 no
pattern,鈥� says Robl. 鈥淚t鈥檚 perplexing.鈥�
Nor are the clones the only victims. The cow that carried calf 1 suffered a
fatal fall in blood pressure after the birth. In fact, 4 of 12 surrogate mothers
in the study died from pregnancy complications. Such deaths still happen despite
improvements to cloning, says Michael Bishop of Wisconsin-based cloning company
Infigen. 鈥淲e sacrifice the cow and the clone . . . all the heroics in the world
can鈥檛 rescue those animals.鈥�
Despite this, some commercial cloners claim that cloning is no more wasteful
than cattle breeders鈥� standard artificial insemination methods. The figures to
date suggest otherwise. While artificial insemination has a 40 per cent success
rate, at best only 5 to 10 per cent of implanted cloned embryos become live
calves. Around 75 per cent die in the first two months of pregnancy but
miscarriages and terminations happen right to the end. And every fourth clone
born is either stillborn or suffers from a lethal defect.
Even clones that survive and look healthy may harbour subtle defects. When
Jon Hill from Cornell University examined the behaviour of newborn cow clones,
he found they scored lower on average than typical cows in tests of
attentiveness and intelligence. And mouse cloners say that one in three clones
born looking normal become massively overweight a few weeks later. 鈥淩esearchers
who study obesity in mice say they have never seen such fat animals,鈥� says Ryuzo
Yanagimachi of the University of Hawaii at Manoa.
Yanagimachi鈥檚 team is now taking a close look at gene activity in newborn
mouse clones. And things aren鈥檛 looking good. 鈥淎ll cloned babies have some sort
of errors,鈥� he says. 鈥淚鈥檓 surprised they can survive it.鈥�
Of course in some species, they don鈥檛 survive at all鈥攚itness the
countless failed attempts to get cloned cat and dog embryos to develop into
living, breathing animals.
Back at the cloning companies, scientists see this outbreak of negativity as
little more than propaganda orchestrated to put off the baby cloners. What
happens with mice is no guide to what happens in other animals, insists Robert
Lanza of Advanced Cell Technology in Worcester, Massachusetts. Lanza says his
company has carried out fresh, and as yet unpublished, tests on virtually every
surviving cow it has cloned and claims they are healthy and normal. 鈥淧eople have
said they don鈥檛 believe there is a single normal clone alive. That is just total
苍辞苍蝉别苍蝉别.鈥�
In any case, say the cattle cloners, even if clones are quite different from
other animals, that doesn鈥檛 make them unhealthy. Infigen has amassed a huge
database of blood tests from apparently healthy cloned cows. 鈥淭he data suggested
to the vets that some of them should be dead,鈥� says Infigen鈥檚 Michael Bishop. 鈥淚
think that shows we don鈥檛 really know what normal is.鈥�
Perhaps. But whether that is the sort of reassurance needed to silence the
sceptics seems debatable when even small imbalances in hormones, proteins or fat
levels could alter the quality of milk and meat. According to Britain鈥檚 Food
Standards Agency, in Europe cloned meat and milk would be classed as novel foods
and so sellers would need a special licence. But unlike GM foods, there is no
legal requirement for cloned food to be labelled. And nothing to stop British
farmers importing cloned cattle.
Meanwhile, there鈥檚 one thing virtually every animal cloner agrees on: human
cloning ought to be unthinkable. The idea of screening cloned embryos for
chromosomal abnormalities, and using imaging to keep tabs on the fetus, is
鈥渟heer nonsense鈥�, says Don Wolf, who is attempting to clone monkeys at the
Oregon Regional Primate Research Center in Beaverton. Fetuses that look robust
at 60 days may die at 61. And a clone that dies after five days of life can have
normal chromosomes and genes while still in the womb. 鈥淗ow in the world,鈥� asks
Wolf, 鈥渨ill they screen out problems when they don鈥檛 know what to look for?鈥�
So far that question has been aimed only at the baby cloners. One day it
could be on the lips of shoppers faced with shelves bulging with milk and meat
from cloned supercows.
