Structural and vascular alterations in placentas from cloned horses and their relationship with placental efficiency

Abstract

The aim of this study was to describe the macroscopic and microscopic characteristics of placentas from cloned horses and to evaluate their placental efficiency compared with placentas from natural pregnancies. Samples were collected from recipient mares that delivered cloned foals (n=10) and from mares with natural pregnancies (n=10). A comprehensive structural (macroscopic and microscopic) analysis was performed, and placental weight, foal birth weight, and placental efficiency were recorded. In the control group, the allantoic surface appeared intact and bluish translucent, while the chorionic surface was reddish and velvety, with evident microcotyledons. In contrast, cloned placentas showed severe structural alterations, including reduction or absence of microcotyledons, amniotic thickening, fibrosis, hematomas, and signs of placental vasculopathy. Despite the viability of cloned foals, they exhibited lower birth weights and reduced placental efficiency, as cloned placentas were significantly heavier than those of controls. Histological analysis confirmed a chronic vasculopathy characterized by concentric perivascular collagen fibrosis, thickening of the tunica media, and luminal stenosis, suggesting decreased maternal–fetal blood flow. These macro- and microstructural alterations may reflect compensatory mechanisms associated with placental insufficiency.