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Embryo transfer: an experimental tool with practical applications.

There are many different aspects of embryo transfer that might be considered for discussion. The theme of this paper is on the use of the technique for experimental work and the possible applications that it may have in domestic animal husbandry. The recovery and isolation of mammalian embryos from the genetic mother and their transfer to a different host mother is now a routine procedure for many experimentalists. The possibilities of this technique for obtaining answers to questions of the influence of prenatal maternal environment and as a means of evaluating the developmental potential of an embryo have long intrigued embryologists, physiologists, and geneticists. Although the present methods may be crude when viewed in retrospect several years hence, they are effective enough to permit a high proportion of embryos of several species to be recovered, isolated, stored, transferred, and to develop in a host mother. Not only has embryo transfer made it possible to obtain many answers of a scientific nature, but also has helped to realize the great potential of application to livestock husbandry. The history of the development of the technique is characterized by several features. First, the developments have usually been studied in litter-bearing laboratory animals such as the rabbit, mouse, and rat; second, the entire process requires that each of several distinct steps be successful in order to achieve a live fetus; third, as in many other fields, progress has been built in a series of steps based on work in several different laboratories and disciplines (Chang and Pickworth 1968, Rowson 1969, Dziuk 1968). The first recorded successful embryo transfer was made by Heape at Cam-