Maintenance of pregnancy in pigs with limited viable embryos

Interest is increasing in assisted reproductive technologies in the pig involving embryo cryopreservation, cloning, and genetic modification. Although inherently inefficient and variable in their outcome, the successful application of these techniques in this species is confounded by unique mechanisms for pregnancy recognition and maintenance that require a minimum number of viable embryos during a critical window of time early in gestation. These mechanisms require both local and systemic interactions between conceptuses and the maternal reproductive axis. Here, we describe a method wherein cotransfer of parthenogenetic embryos with the capacity for limited development can be used to sustain the pregnancy of fewer than four viable conceptuses to term.