Abstract：Yak (Bos grunniens) has a typical cotyledon placenta which undergoes changes from formation, growth, and maturation during pregnancy, and it is the link between maternal and fetal during pregnancy. It is play an important role in the exchange of nutrients and metabolic waste, hormone secretion. Studying on the relationship between the phenomenon of apoptosis and the main physiological function in the placentome is very improtant for analyzing the mechanism of dynamic development of yak placentome in the angle of apoptosis. Placenta tissues during pregnancy, pre and post parturation of 4 ~ 8-year-old yaks were collected. They were paraffin-embedded and HE dyeinged to observe the changes of placental structure in all stages of pregnancy. The apoptosis of yak placental tissue was observed and analyzed by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and 4,6-diamidino-2-phenylindole (DAPI) dyeing technology. The structure of yaks placentomes during pregnancy was constantly changing, so the different stage of gestation could present different morphological characteristics. Yaks had formed a typical structure of the epithelial chorionic placenta in 45 days of pregnancy. With the progress of pregnancy, fetal villi gradually branched and deeply into the maternal caruncula crypts. The number of binucleate cell was increased in placentomes gradually. Caruncula crypt epithelium in 6 months of pregnancy began to appear obviously degenerative changes, such as cell vacuolization. The entire crypt epithelium was not found at pre-parturition. Yak placentomes existed in obvious apoptosis phenomenon. Fetal villi epithelium and maternal crypt epithelium was the main distribution of TUNEL positive cells during gestation and uterine meat Fu matrix had a very small amount of apoptotic cells in early stage of gestation. With the grown of the fetus, TUNEL-positive cells in the two layer epithelial tissue generally showed an upward trend, and the maternal crypt epithelium was significantly lower than the fetal villus epithelium. Fetal villi epithelium was significantly higher in the pre-delivery and achieve maximum after delivery. The experimental study found that yak placentomes processed in a series of changes about the morphological structure from the formation, growth and maturation of physiological. Its apoptosis plays an important role in the normal renewal of cells and structural changes of placental tissue, and the result provides a theoretical data for solving the problems such as abortion appearing in the yak production process.
