Cloned sheep, which are created by a technique called somatic-nuclear cell transfer, age normally, suggests a study published in Nature Communications. The analysis of 13 aged cloned sheep, including four created from the same genetic material as the first cloned animal, Dolly the sheep, represents the first long-term study of the health effects of cloning in a large animal.
Dolly the sheep, who was born 20 years ago (in July 1996), died at a comparatively young age of 6.5 years, having suffered from osteoarthritis. This outcome has raised concerns that cloned animals may age more quickly, or less healthily, than normal offspring.
Kevin Sinclair and colleagues studied 13 cloned sheep between 7 and 9 years of age. Four of the animals were cloned using nuclei from the same mammary-gland cell line as Dolly, so are effectively clones (or genomic copies) of Dolly. The authors performed musculoskeletal assessments, metabolic tests and blood pressure measurements, as well as radiological examinations of all main joints in the cloned sheep and compared them to control sheep (5 and 6 years old). All cloned sheep are still alive and healthy, showing only mild or, in one case, moderate osteoarthritis. The animals also show no signs of metabolic diseases, and have normal blood pressure.
Although the authors could not compare the cloned sheep with normal animals of exactly the same breed and age, and did not measure molecular markers associated with ageing, the study provides the strongest evidence yet that large cloned animals age normally. These findings provide important information about the safety of cloning and its long-term effects on animal health.