In Vitro development of preimplantation embryos from domestic species

In recent years, the development of methods for the genetic manipulation of domestic species has generated a rapidly increasing demand for pre-attachment embryos. The limited prolificacy of these species makes superovulation and surgical recovery of embryos necessary. However, these techniques are too expensive and labour-intensive to be used routinely for supplying enough material for experimental or commercial applications. This has provided the thrust for an unprecedented effort to develop methods for the culture of embryos derived from in vitro maturation and fertilization of oocytes collected from slaughtered animals. Offspring generated in vitro have been obtained using cattle, goats, pigs and sheep, but the efficiency and reliability of the techniques and the quantity of the embryos vary between species. At present, the best results can be obtained in ruminants, while pig embryos have proved to be more difficult to generate. Although many obstacles have been overcome simply by empirical trials and observations, the availability of high numbers of easily accessible embryos has also led to a substantial advance in our knowledge of their physiology. This has therefore widened the range of experimental models that can effectively be used in developmental studies, especially since, in some cases, models using these species may be more relevant to human embryology than those using rodents.