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BIOTECHNOLOGY
The possibility of cloning humans has raised questions as to whether nuclear transfer can be used to reproducibly generate healthy adult animals. Reports in the popular and scientific press on genetic, immunological, and other developmental problems raise the question of whether there are "any normal clones in existence" (1-4). We evaluated a series of 24 sexually mature cattle, cloned from nonquiescent somatic cells as described (5, 6).
A total of 496 blastocysts were transferred into progestin-synchronized recipients, and 110 of the 247 recipients (45%) were pregnant as determined by ultrasound 35 to 40 days after transfer. Eighty of these spontaneously aborted (73% compared with 7 to 24% for in vitro fertilization-derived pregnancies) (7), 30 developed to term (Web table 1) (8), and six died shortly after birth (Web table 2) (8). Necropsy results indicated that five of six deaths were due to cardiopulmonary problems secondary to placental insufficiencies; one calf died from enteric complications 149 days after birth. The remaining 24 Holstein cattle (80%) were vigorous (45 +/- 2 kg at birth compared with 43 kg normal weight) (9) and remain alive and healthy 1 to 4 years later [survival from birth to reproductive maturity normally ranges from 84 to 87% (10, 11)].
Results of physical examination were normal for all animals, including objective (temperature, pulse, and respiratory rate) and subjective (general appearance, eyes, lymph nodes, and cardiac and pulmonary auscultation) findings. Results of abdominal palpation per rectum (reproductive and gastrointestinal organs and kidneys) were normal. Body condition scores (1 = thin, 5 = fat) averaged 3.25...