Equine Cloning Expert Reviews Successes, Challenges

Cutline for accompanying photo:The University of Idaho's three mule clones strive to outrace each other in their pasture. The photo was taken in June 2004.Please credit the photo to: Kelly Weaver/University of Idaho © 2004

Newswise — Successful births and vigorous offspring are the rule for equine clones, University of Idaho veterinary scientist Dirk Vanderwall said Jan. 10, but pregnancies still are challenging to establish.

Smithsonian National Zoological Park researcher Budhan S. Pukazhenthi and Vanderwall were invited to address advances in biotechnology and species conservation during the annual conference of the International Embryo Transfer Society in Orlando, Fla.

Losses of cloned mule and horse embryos during early pregnancy do not translate into the health problems seen at birth or in newborns of other livestock species, Vanderwall said.

The loss of more than 80 percent of embryos early in pregnancy is consistent in animal cloning overall. Vanderwall said, "We see some similarities in equine cloning, but we are not seeing the problems at birth or shortly after birth that have been reported in cloned sheep and cattle."

The University of Idaho's three mule clones are healthy and vigorous as three-year olds. Two, Idaho Gem, the world's first equine clone, and Idaho Star, are now in training for competitive racing later this year.

The third mule clone, Utah Pioneer, will be displayed Feb. 18 in St. Louis at Family Science Days during the American Association for the Advancement of Science annual meeting.

The three mule clones were produced by a team led by Dr. Gordon Woods, UI Northwest Equine Reproduction Laboratory director, that included UI's Vanderwall, Utah State University animal scientist Dr. Ken White and Coeur d'Alene veterinarian Dr. David F. Tester.

Scientists elsewhere also have reported the successful birth of three horse clones.

The Idaho team documented a 2.7 percent foaling success rate with the cloned mule embryos. In 2005, a Texas A&M University team reported a .7 (seven-10ths) percent foaling success rate with cloned horse embryos.

"Clearly, further work is needed to increase the efficiency of equine cloning," Vanderwall said.

Vanderwall presented data during the Orlando meeting that showed late-term pregnancies of cloned embryos can be assessed in horses by monitoring the combined thickness of the uterus and placenta.

In the case of the three mule clones, ultrasound measurements showed the uterus-placenta thickness was within the normal range during the months before the successful births.

Early pregnancy monitoring with ultrasound showed that of 28 cloned mule and horse embryos detected by the Idaho team, 25 had failed within 80 days. The gestation period for horses is about 330 days, and is closer to 350 days for mules.

Most cloned embryos were generally lost in the earliest phase with no previous indication of trouble, Vanderwall said. Once an actual embryo was established, several symptoms signaled impending loss, including lack of a heartbeat, failing membranes, change in the ultrasonic echo and the physical size of the embryo.

Genetic programming errors were the most likely source of losses in the early stages of cloned equine pregnancies, Vanderwall said.

Animal cloning offers several potential applications, Vanderwall said. They include preserving genetics from animals otherwise unable to reproduce, saving exotic species such as Przewalski's horse or "biopharming" to produce transgenic animals.

In horse breeding, cloning can salvage the genetic heritage of geldings, stallions that were castrated to make them easier to train. Many horse breed associations rule out the registration of clones, but equine sports such as dressage and eventing typically are open to all horses regardless of their breed.

Vanderwall was named theriogenologist of the year in 2005 by the American College of Theriogenologists, which is composed of veterinary specialists focused on animal reproduction.

An associate professor of animal and veterinary science in the Northwest Equine Reproduction Laboratory in the UI College of Agricultural and Life Sciences, Vanderwall earned his veterinary degree from Cornell University in 1986. He then worked for a standardbred horse breeding farm in New York.

He earned a doctorate in animal physiology from UI in 1992 and became a diplomate of the American College of Theriogenologists in 1993. He completed a two-year post-doctoral fellowship at the University of Kentucky in 1994. He joined the faculty of the Colorado State University before returning to Idaho in 1999.