Endocrine characteristics of cloned calves

To examine the possible link between endocrine status and perinatal problems related to cattle cloning, plasma concentrations of cortisol, adrenocorticotropic hormone (ACTH) and components of the insulin-like growth factor (IGF) system were compared between 13 somatic cell cloned and seven control Japanese Black calves (five produced by artificial insemination [AI] and two produced from in vitro fertilized embryos [IVP]) immediately after birth. Five cloned calves required delivery by cesarean section (C-section), while all of control calves were delivered by spontaneous vaginal delivery. The C-section delivered clones were heavier at birth, followed by vaginally delivered clones and IVP controls, and AI controls were the lightest. The neonatal mortality (death within the 1st week) of C-section delivered clones was also high (4/5) compared to that of vaginally delivered clones (1/8) or controls (0/7). Plasma concentrations of cortisol and IGF-I were lower in the clones than control calves although the plasma ACTH level was not different between the groups. A striking difference was observed in plasma IGF binding protein (IGFBP) profile in which cloned calves had a greater relative abundance of IGFBP-2 compared with controls. Observed differences suggest that insufficient prepartum rise in plasma cortisol of cloned calves failed to initiate the switch to an adult mode of the IGF system during late gestation and therefore parturition was not spontaneous. Inappropriate developmental changes in endocrine system may be partly responsible for the fetal overgrowth and perinatal complications associated with the cloning technology.