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Calves produced from cloned embryos have been characterized by high birth weight and low survival rate. The cause of these problems has not been identified. In this study 40 Brangus calves from embryos cloned by a nuclear transfer technique were delivered by caesarean section during naturally initiated parturition. They were treated medically to maximize survival rates when life-threatening physiologic abnormalities were recognized. Birth weight ranged from 26.4 to 67.3 kg. Most calves were slow to stand and had poor suckling behaviors. One or more of the following physiologic abnormalities were measured in 34 of 40 calves during the first hour of life: hypoxemia, hypoglycemia, metabolic acidosis, and/or hypothermia. These abnormalities were sufficiently severe to warrant medical treatment. Only one calf died in the immediate postnatal period (29 hr of age). The cause of death in six of the eight calves that …