Evaluation of Gestational Deficiencies in Cloned Sheep Fetuses and Placentae1

Abstract

Sheep fetal development at 35 days of gestation was examined following natural mating, in vitro production (IVP) of fertilized embryos, or somatic cell nuclear transfer (NT). Five crossbred (Blackface x Black Welsh) and four purebred (Black Welsh) fetuses and their associated placentae produced by natural mating were morphologically normal and consistent with each other. From 10 ewes receiving 21 IVP embryos, 17 fetuses (81%) were recovered, and 15 of these (88%) were normal. The NT fetuses were derived from two Black Welsh fetal fibroblast cell lines (BLW1 and 6). Transfer of 21 BLW1 and 22 BLW6 NT embryos into 12 and 11 ewes, respectively, yielded 7 (33%) and 8 (36%) fetuses, respectively. Only three (43%) BLW1 and two (25%) BLW6 NT fetuses were normal, with the rest being developmentally retarded. The NT fetal and placental deficiencies included liver enlargement, dermal hemorrhaging, and lack of placental vascular development reflected by reduced or absent cotyledonary structures. Fibroblasts isolated from normal and abnormal cloned fetuses did not differ in their karyotype from sexually conceived fetuses or nuclear donor cell lines. Our results demonstrate that within the first quarter of gestation, cloned fetuses are characterized by a high incidence of developmental retardation and placental insufficiency. These deficiencies are not linked to gross defects in chromosome number.