A foal born earlier this year named Prometea is the first successfully cloned horse, scientists report today in the journal Nature. What is more, the horse from which the original cell material was taken--not a surrogate--gave birth to her. The birth also challenges the idea that the early success of a pregnancy depends on the mother's immune system responding to a developing fetus and placenta as something different from itself.

Cesare Galli and his colleagues at the Laboratory of Reproductive Technology in Italy engineered male and female cell lines from skin biopsies of two horses, a male Arabian thoroughbred and a female Haflinger. A total of 841 embryos were constructed using the same nuclear transfer technique that led to Dolly the sheep. Of these, 22 developed into blastocysts, or hollow spheres of 100 or so cells. The scientists then implanted 17 of the blastocysts into nine female horses, which resulted in four pregnancies. Prometea, born on May 28, 2003, was the only one to survive to full term and so far, she is in good health. "Our result adds the horse to the list of mammals that have so far been successfully cloned from an adult somatic cell," the authors note.

The legacy of championship racers and show horses could conceivably live on forever if reproducible copies are indeed feasible. The scientists conclude that "in principle, cloning could enable gelding champions [castrated horses] to contribute their genotype to future generations, as well as opening up an opportunity to verify the reproducibility of traits such as character and sporting performance."