| Cloning technology offers new possibilities for agriculture, medicine and the study of fundamental developmental processes. Application of this technology is limited by inefficiencies of the nuclear-transfer procedure, high rates of abnormal pregnancies and fetal loss, and concerns about the health and longevity of resulting animals. To understand further factors that may influence the outcome of the nuclear-transfer process, experiments were conducted to compare the effect of the nuclear-donor cell stage of differentiation by testing cells of the follicular cell sequence: preantral follicle, cumulus, granulosa, and luteal. Two cell types in the sequence, preantral follicle and luteal, were previously untested for cloning proficiency and were demonstrated competent to support development of cloned embryos into the last trimester of gestation. Cloned bovine embryos derived from preantral follicle cells, the least differentiated cells in the lineage, were less likely to develop to the blastocyst stage but more likely to survive the preimplantation period, confirming previous results from research with mice. Additional experiments were conducted to compare physiological differences between cloned and embryo transfer control calves at birth and during the 48-hour period immediately thereafter. Cloned calves were similar to controls for many parameters studied. Notable exceptions included developmental delays of important physical adjustment parameters, hypoglycemia, anemia, enlargement of the umbilical region and problems with thermoregulation. With appropriate clinical intervention, all the cloned calves in the present study survived the first 48-hour neonatal period. Placentas of cloned calves contained fewer total placentomes; however, mean placentome mass and surface area were greater. Phenotypically, cloned placentas differed from controls in the percentage of placentomes classified Type A (engulfing mushroom-like; controls > clones) and Type C (flattened; clones > controls). Other placental anomalies observed included edema, teratomas, enlarged vasculature, and areas devoid of placentation. During the preweaning period (birth to 60 days) cloned calves were observed with higher incidence of umbilical infections most likely related to the placental abnormalities observed at birth. Cloned calves were more variable in rectal temperature, heart rate, and respiratory rate and were observed with increased frequency and severity of disease. Seventy-five percent of cloned calves failed to survive; 100% of controls under similar management survived the preweaning period and subsequently. |
