New Observations regarding Staging Turkey Embryos from Oviposition through Primitive Streak Formation

Abstract

The normal developmental sequence of the turkey embryo from the initial cleavage divisions through hypoblast formation has been described previously in 11 separate stages based on the progressive morphological differentiation of the embryo (Gupta and Bakst, Turkey embryo staging from cleavage through hypoblast formation. J. Morphol., 217, 313–325, 1993). However, in recent preliminary studies, our attempts to apply this stage table to describe the stages of embryo development were not successful. Therefore, we re-evaluated the development sequence of the turkey using eggs obtained from modern day commercial lines. Embryos from unincubated eggs and eggs incubated at different time intervals up to 25 hour were examined. In contrast to the observations by Gupta and Bakst, embryos from unincubated eggs lack an area pellucida (AP) but are characterised by dense clusters of cells that do not begin to dissipate and begin forming the AP until after 3–4 hours of incubation. Koller's sickle may or may not be present prior to and during hypoblast formation. Based on these new observations, a revised stage table including the above observations is presented to reflect more accurately the development of the modern commercial turkey embryo.