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Embryonic stem cells (ESCs) are derived from the inner cell mass of preimplantation blastocysts. For decades, attempts to efficiently derive ESCs in animal livestock species have been unsuccessful, but this goal has recently been achieved in cattle. Together with the recent reconstitution of the germ cell differentiation processes from ESCs in mice, these achievements open new avenues for the development of promising technologies oriented toward improving health, animal production, and the environment. In this article, we present a strategy that will notably accelerate genetic improvement in livestock populations by reducing the generational interval, namely in vitro breeding (IVB). IVB combines genomic selection, a widely used strategy for genetically improving livestock, with ESC derivation and in vitro differentiation of germ cells from pluripotent stem cells. We also review the most recent findings in the fields on which IVB is based. Evidence suggests this strategy will be soon within reach., (© The Author(s) 2018. Published by Oxford University Press on behalf of Society for the Study of Reproduction.)

Animals with extreme body growth frequently experience poor reproductive performance, but the cause for this association has not been clearly established. A line of mice homozygous for the high growth (hg) mutation, a mutation that has a major effect on post-weaning growth, exhibits several reproductive deficits including an abnormally high incidence of luteal failure. The objective of the present study was to investigate luteal failure in high-growth (HG) mice during pregnancy and to determine whether the cause of the apparent luteal failure resides in the ovary or the hypothalamic-pituitary unit. In HG females with a demonstrated history of infertility, progesterone injections (1 mg s.c. daily) beginning on Day 1 postcoitum (p.c.) increased the proportion of animals pregnant at Day 17 of gestation. Twice-daily injections of 100 microgram of ovine prolactin (PRL) in alkaline saline given to another group of females beginning on Day 1 p.c. increased the proportion of HG females that were pregnant on Day 6 of gestation compared with saline-injected HG females, although PRL did not increase the pregnancy rate in HG females when compared with a group of noninjected control females. When ovaries from HG females were transplanted into ovariectomized congenic C57 hosts, the C57 graft hosts displayed normal estrous cycles, and upon mating the majority of graft hosts became pregnant. In contrast, when ovaries from C57 females were transplanted into ovariectomized HG hosts, the HG graft hosts displayed normal estrous cycles, but upon mating most were unable to maintain pregnancy. These results suggest that the hypothalamic-pituitary unit of the HG female provides an inadequate signal to the ovaries to maintain pregnancy. Luteal failure in HG females may be due to insufficient PRL as required for establishment and early maintenance of the CL during pregnancy in mice.