Some one to four years after birth, 24 cloned cows appear normal and healthy, scientists say. The findings, which will be published in the November 30 issue of the journal Science, stand in contrast to earlier reports of genetic, immunological and developmental defects in cloned animals. According to researchers involved in the work, the results demonstrate that cattle producers should be able to use their cloning technology to safely replicate their best animals. Moreover, they affirm the potential of cloning for medicine.
Investigators led by Robert P. Lanza of Advanced Cell Technology in Worcester, Mass., implanted 496 cloned embryos into 247 cows. Some 35 to 40 days after the transfer, 45 percent of the cows were shown to be pregnant. Only 30 of the clones developed to term, but of these 24 survived to adulthood and have passed the full spectrum of health tests with flying colors. This 80 percent success rate among the cloned cows approaches that of normal rates of survival from birth to adulthood, which range from 84 to 87 percent. The team further notes that the animals seem behaviorally and reproductively normal. In fact, two of the cloned animals have given birth to their own calves, which themselves appear normal in every way.
"Several of the cloned calves experienced pulmonary hypertension and respiratory distress at birth, and fever after vaccinations at four months," the researchers write. "However, we did not observe genetic defects, immune deficiencies, gross obesity or other drastic abnormalities cited by other researchers." Whether these previously reported defects occur in other species or stem from differences in cloning techniques¿or some combination of the two¿they conclude, remains to be determined.