Early ontogeny in the llama (Lama glama): Morphofunctional characterization of the preimplantation blastocyst.

South American camelids are domestic species native to the Andean region and display distinctive reproductive features relevant to their productive management. Although embryo transfer has been adopted as a genetic improvement tool, important knowledge gaps persist regarding embryo quality assessment and early embryonic morphophysiology. This study aimed to describe morphometric characteristics, steroidogenic capacity, and the presence of primordial germ cells in preimplantation llama embryos. Sixteen adult females were superovulated with 650 IU equine chorionic gonadotropin (eCG) and used as embryo donors. Embryos were recovered non-surgically on days 7, 8, and 10 post-mating, yielding a total of 32 embryos. Sixteen embryos were processed for histological and immunohistochemical analyses. Embryos were photographed, analyzed using ImageJ-FIJI®, and classified according to shape and size as spherical, irregular, elongated, or filamentous. Histological sections were stained with haematoxylin-eosin and periodic acid-Schiff, and embryo dimensions and trophoblastic wall thickness were recorded. Immunohistochemical detection of P450 aromatase and DDX4 was performed. Day 7 embryos were spherical or irregular, day 8 embryos exhibited spherical, irregular, and elongated forms, and day 10 embryos were exclusively filamentous. All embryos were hatched blastocysts lacking the zona pellucida. Mean embryo diameter increased markedly with developmental stage. Aromatase immunoexpression intensified with development and was localized to trophoblastic cells, whereas DDX4-positive cells were detected within the inner cell mass. These findings provide novel insights into early llama blastocyst biology and support the development of objective embryo evaluation criteria in South American camelids.