Disclosed herein are cultures of undifferentiated avian primordial germ cells/blastodermal cells. The cultures are capable of maintaining their undifferentiated characteristic and also their capability of expressing the EMA-1 epitope for extended periods when cultured in the presence of an isolate from avian navel (e.g. turkey navel extract). Methods of culturing such cultures using avian navel extracts, and culture media containing avian navel extract are also disclosed. Recombinant birds derived from these cultures are also disclosed. These cultures can be frozen for long-term preservation of germ line genomes.