WEDNESDAY, Sept. 5, 2001 (HealthDayNews) -- Add pigs to the catalog of cloned animals at Texas A&M University.
A piglet litter, born Aug. 12, joins previously cloned cattle and goats, the College of Veterinary Medicine announced today.
Dogs, cats and horses may be next, researchers there say.
"None of these, of course, are the first [to be cloned] in an animal group," says James Womack, the director of the university's Center for Animal Biotechnology and Genomics, located in College Station, Texas. "But this is -- and I say this with pride -- the first time one academic institution in the world has cloned three different species."
So, why all the fuss?
Cloned pigs could be very useful for humans, says Robert Foote, professor of animal physiology at Cornell University in Ithaca, N.Y. "Pigs are relatively difficult to clone; only four institutions have been successful and have only produced small numbers of progeny," he says. "But pigs could be important because of the interest in organ donation."
"If you could clone a genetically engineered pig that could be used potentially for organ donation, that could be very helpful," Foote says.
And Texas has a few more in the works.
"There are three litters so far, and we have two [more] sows who are pregnant," says lead researcher Jorge Piedrahita, associate director of the animal biotech center. "It took three times to get those litters. We have made several modifications [to the cloning process] that have made a tremendous difference in the success rates of the pregnancies, as well as in the number of piglets we are getting per embryo transfer. We are now getting between 80 and 100 percent of pregnancies from this technology."
Texas A&M says a cloned Boer goat, aptly named Second Addition, was born March 29, 2001. She has similar color markings to her 8-year-old donor, as well as a similar disposition, the researchers say.
In 1999, the school cloned a calf from the oldest animal ever used in the procedure and also created an Angus calf, named 86 Squared, which was specifically cloned for disease resistance. The calf was born in 2000.
Since the first cloned mammal in 1997, Dolly the sheep, researchers around the world have cloned all sorts of animals, from mice to monkeys. But the process is far from perfect: Many cloned embryos die while still in the womb, and some of the offspring that are born are beset with any number of health problems, from respiratory failure to extreme growth.
But Piedrahita says the pig litters have been healthy.
"We had three litters which produced 20 piglets each, and we lost 10 of the piglets," he says. "But none of those had any development problems or abnormalities. [Rather], we had a husbandry problem. Two of the mothers would not take care of the piglets, and that's because we had to intervene so much in looking after the piglets that the mothers rejected them. We had to hand raise them, and that's always difficult."
The pigs were created by essentially the same cloning method used to create Dolly, Piedrahita says. Known as "nuclear transfer," the nucleus from the donor mammary cell was fused with a different pig's egg cell that had had its nucleus removed. The cells are fused by placing them side-by-side and passing a tiny electrical pulse through them, enough to temporarily open the cellular membrane of the egg cell so the other cell's nucleus can pass through.
"We are concentrating on cloning animals for two practical reasons," Womack explains. "Cloning animals gives you a powerful experimental tool. Multiple animals that are genetically identical allow you to do experiments that can determine the relative role of genetics and environment, and that can apply to any complex trait -- reproduction, growth, behaviors, anything that might have a genetic or environmental influence."
"Second, there's a real advantage in agriculture to duplicate animals that are the elite -- whether it's a dairy bull who can sire outstanding daughters for milk production or a bull steer who can produce terrific cattle for beef," Womack says. "In the past, we've been able to artificially select for certain traits and create outstanding animals, but they don't always run true to form."
But don't expect to see cloned animals at your local farm just yet, adds Foote. "It's still a very experimental process, and it's very inefficient and very expensive."
And there's still lots of research to be done on cloning, he says.
"This is still a very inefficient process," Foote says. "The progeny that are born, there's still a substantial portion of them that die. The reprogramming of the genetic material is incomplete, and that causes problems."
Using cells from older animals also is problematic, Foote says. "Those cells have to go through a lot of transformation -- a lot of turning on and off," he says. "So, there's greater manipulation of the cells, a bigger workload to reprogram the genes -- and even a small percentage of mistakes can prove to be very serious."
Womack agrees that the cloning process is not yet perfect.
"No, not all the bugs are worked out," he says. "Some animals have yet to be cloned, which is one of the reasons we are so interested in cloning multiple species. We're trying to learn what's alike and what's different in these cloning processes."
"That's why we're still working to clone dogs, cats and horses: It's to learn more about the reproductive physiology of these animals," he says.
What To Do
For everything you could want to know about cloning, check out the NewScientist Clone Zone. For more on the ethical debate surrounding cloning, see Bioethics.net.
And for more on the ewe that started it all, take a look at this article from Scientific American.
