Cloned non-human mammalian nuclear transfer units, embryos and animals are provided by introducing a contact-inhibited non-cycling mammalian donor cell in the G1 state or a nucleus thereof into an enucleated oocyte from a non-human mammal of the same species as the donor to form a nuclear transfer unit, implanting the nuclear transfer unit into the uterus of a surrogate mother, permitting the nuclear transfer unit to develop into the cloned non-human mammalian embryo and allowing the embryo to come to term.