Postnatal characteristics of calves produced by nuclear transfer cloning

Abstract

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 died or were euthanized in the first 14 weeks of life was related to bacterial infection. Because the calves' clinical abnormalitites in the immediate postpartum period could be caused by defective energy metabolism, additional plasma analytes were measured retrospectively. There was sufficient sample available from 21 calves (20 male, 1 female). Plasma growth hormone, insulin-like growth factor-1, cortisol, glucagon, glucose, and free fatty acid concentrations in clone calves were not different from those of a reference population (P > 0.05). Thyroxine and triiodothyronine concentrations were lower (P < 0.05) and insulin concentrations higher (P < 0.05) in clone calves than in the reference group at 10 min after birth. None of the analytes from clone calves at birth or 10 min was significantly correlated to birth weight, except for glucagon (R 2 = 0.184 at birth; R 2 = 0.449 at 10 min). The findings were interpreted as an abnormality of in-utero energy regulation, causing abnormal growth rate and poor preparation for extrauterine life.