In that time, these cattle developed long bodies and short, sturdy legs. When the cattle became so numerous that they were harmful to the island's ecosystem, the government ordered the herd destroyed. A female named Lady, however, was not destroyed, and scientists harvested the semen from ten bulls, in the hope of establishing the unique herd in another location. Before this could be accomplished, Lady had grown older, and the birthing process became hazardous for her.
Cloning Lady and then implanting her zygotes into surrogate mothers was considered safer. The scientists and an organization called the New Zealand Rare Breed Conservation Society hoped to inseminate females cloned from Lady with the preserved semen and start a new generation of these cows. By 2006, there were seven “pureblood" Enderby cattle — all clones of Lady. Embryos from three of these, fertilized with semen taken from the bulls on Enderby Island in 1991, were implanted in cross-recipient (different breed) cows. Six purebred Enderby calves were produced,including three bulls.
Despite the many successes in cloning around the world, cloning techniques are probably not advanced enough to produce a human today. The success rate in the rhesus monkey experiment was three to four percent of pregnancies. What success rate would be acceptable in humans? Considering how devastating it is to lose a child during pregnancy, cloning techniques would have to render success rates as high as or higher than that of clinical fertility-enhancing procedures to be acceptable to even the most desperate parents.
Pregnancy, in the case of Dolly, was complicated by another poorly understood effect of the cloning technique — high gestational birth weight. Dolly weighed one-third more than a normal lamb, and researchers at the Roslin Institute were even criticized for having Dolly's zygote implanted in a smaller breed of sheep.