Early development of the chorioallantoic membrane and cotyledons in the water buffalo (Bubalus bubalis)

The villous synepitheliochorial placenta of ruminants is formed by close interaction between fetal and maternal tissues and complex cell differentiation mechanism. Whereas the bovine is extensively studied, for the buffalo as close relative early stages of placental differentiation are unknown. We investigated the early development of the chorioallantoic membrane (CM) and cotyledones in water buffalos. In total, 33 individuals with gestational ages from 15 to 58 days were studied by means of gross anatomy, histology, immunohistochemistry and electron microscopy. Data so far show that until 30 days the CM was smooth and thin. At 15-19 days, the CM had cubic epithelial cells associated with a very thin layer of collagen fibers towards the mesenchyme and a few small vessels. At 21-24 days, this layer increased in volume, as well as the number of vessels. Small folds as precursor of the villi occurred associated with dispersed binucleate trophoblast giant cells (TGCs). Abundant short villi were present at 26-32 days, characterized by a stratified cellular layer of small round cells and numerous TGCs. At 32-36 days, regions with dark color represented the origin of the cotyledons. They were villous at 45 days; especially in the middle of the CM. At 51-58 days, the cotyledons had increased in number and size and were distributed in rows along the caruncles of the CM. They possessed prismatic epithelium in the basal axis and numerous wellvascularized villi and projections. As occurred for bovine years ago, due to the role of CM for the successful of gestation, our results may contribute to the understanding and improvement of reproductive technologies applied to the in vitro buffalo embryo production, in order to compensate problems related to the low efficiency of superovulation and embryo transfer in this species.