Understanding of ruminant placental structure and function is essential for veterinarians and researchers. The ruminant placenta is classified as cotyledonary and synepitheliochorial on the bases of its gross anatomical features and histological characteristics respectively. The richly vascularized embryonic chorioallantois is lined on its outer surface by cells of the trophectodermal epithelium. These cells which assume specialized functions are referred to as trophoblast cells. Two morphologically and functionally distinct cell types have been recognized in the trophectoderm of the placenta of ruminant animals. These are the mononucleate trophoblast cells and the binucleate trophoblast cells. The occurrence, morphological characteristics, and specialized functions of these trophoblast cells, in relation to conceptus nutrition and survival in utero are discussed in this review.

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