This investigation was carried out to study the equine placenta from early gestation to near term, with special reference to morphological changes associated with the development of the vasculature of the fetal component of the microcotyledons. Pregnant uteri were removed post mortem from five Thoroughbred mares between 110 and 309 days of gestation, two of which were aged, multiparous animals suffering age-related degenerative changes in their endometrium (endometrosis), while the other three were young, and had primigravid normal healthy uteri. Pieces of endometrium with placenta attached were fixed for light microscopy and fetal vascular casts were made by injecting the placental arteries with a mixture of Mercox and methylmethacrylate. The casts were examined under the scanning electron microscope. In an aged, endometrotic mare at 110 days of gestation, most of the microplacentomes were irregular in shape with a mean±sem diameter of 399±30.53μm. Capillaries with variable diameters made up widely meshed network villi with pointed ends (Type 1 terminal villi), and narrow-meshed networks with finger-like ends (Type 2 terminal villi). In the “paired” young healthy mare at day 121 of gestation, most of the microplacentomes were globular in shape and appeared smaller in diameter than those in the 110-day “pair”. The narrow-meshed capillary networks formed villi with stems that consisted of both intermediate and terminal parts, the latter of which represented more the Type 2 than the Type 1 terminal villus. In another aged endometrotic mare at 179 days of gestation, the microplacentomes were typically globular in shape and they showed a mean diameter of 534±36.07μm. The villi were short and thick and they were distinctly differentiated into stem, intermediate and terminal parts. The density of the fetal capillaries had now greatly increased so that, three dimensionally, they constituted bulb-like capillary networks at the base of the stem of each villus. At 199 days in the young healthy “pair”, the microplacentomes were again smaller in diameter (402±16.24μm) than in the old mare at 179 days and the interhaemal distance had now reduced to 14.28±0.42μm. The vascular density was lower than in the day 179 aged mare and the fetal villi were much longer and thinner. In the single late stage, healthy young mare at 309 days of gestation (term=336days), the microplacentomes, each of around 2mm diameter, exhibited maximal length villi. The capillaries were arranged simply, mostly in straight lines along the axis of the villus, and with communications visible at irregular intervals. Simple and slightly more complicated side capillary loops could be seen along the whole length of the villi and at the top of the terminal villi. Most of the capillaries were characterized by zones containing dilated sinusoids, which increased the surface area for materno-fetal exchange. Thus, the morphological development of the microplacentomes on the surface of the horse placenta during gestation was studied, with special reference to the growth and organisation of the fetal and maternal capillary beds within each microplacentome. The study also reinforced previous work showing the disadvantageous influence of age-related endometrial degenerative changes on microplacentome development and on both the extent and intimacy of physical and haematological contact at the fetomaternal interface, and hence upon fetal growth.

Comparison has been made between glycans at the fetomaternal interface of two Tayassu species (New World peccaries or wild pigs) and those of swine (true pigs) and dromedary, which have similar epitheliochorial placentae. Plastic sections of near-term fetomaternal interface from Tayassu tajacu (120 days gestation) and Tayassu pecari (140 days gestation) were stained with 20 lectins and compared with those of swine (109 days) and dromedary (375 days). Both Tayassu species showed similar staining characteristics, which differed only slightly from those of the swine. Most differences were quantitative rather than qualitative, except for binding of Arachis hypogaea lectin to terminal beta-galactose which was absent in swine uterine epithelium though present in both Tayassu species, and binding of Sambucus nigra lectin to sialic acid which was absent in swine epithelium and trophoblast though present in Tayassu. Glycosylation of the dromedary fetomaternal interface showed, in contrast, significant differences compared to Tayassu and swine, particularly regarding fucosyl, sialyl and terminal galactosyl residues. Despite a divergence of between 33 million and 37 million years between true pigs and peccaries, glycosylation of the fetomaternal interface has remained similar, with most of the observed changes affecting terminal structures. The dromedary has an epitheliochorial placenta with a similar architecture, but different glycan expression, suggesting modification of glycosyl transferases with evolution. These data contain clues to changes of glycosyl transferase activity that accompany speciation.

This study aimed to elucidate development of the areola in the early dromedary placenta in comparison with that of the pig and mare. Placental tissues from 25 pregnant camels were obtained from Cairo abattoir and prepared for light, scanning and transmission electron microscopy by routine methods. Vascular casts were made by injection of 4 : 1 liquid plastic mixture of mercox and methylmethacrylate. Areolar formation was first observed at 4.5 cm curved-crown-rump CVR length, while by 5-9 cm CVR length, the endometrial surface was uneven and studded with numerous uterine gland openings, where corresponding foetal areolae were barely detectable and the foetal areolar cells were of variable appearance and covered with long microvilli. At 10-13 cm CVR length the uterine gland openings developed irregular folds and the maternal areolar cells showed numerous apical blebs. At 14-29 cm CVR length the foetal areolae showed a great increase in height at the expense of their width. At 30-34 cm (CVR) length the maternal areolae appeared discoid and sharply demarcated from the surrounding inter-areolar tissues and the foetal areolae were rounded to irregular in shape with well-developed areolar rims. The vascular casts showed a widely meshed capillary network on the maternal areola, connecting with the pre- and post-capillary vessels, whereas the foetal side showed a relatively dense capillary meshwork. These studies indicate that the areola in the placenta of the one-humped camel is of the regular type like in the pig, and is poorly vascularized.

This study aimed to elucidate development of the areola in the early dromedary placenta in comparison with that of the pig and mare. Placental tissues from 25 pregnant camels were obtained from Cairo abattoir and prepared for light, scanning and transmission electron microscopy by routine methods. Vascular casts were made by injection of 4 : 1 liquid plastic mixture of mercox and methylmethacrylate. Areolar formation was first observed at 4.5 cm curved-crown-rump CVR length, while by 5-9 cm CVR length, the endometrial surface was uneven and studded with numerous uterine gland openings, where corresponding foetal areolae were barely detectable and the foetal areolar cells were of variable appearance and covered with long microvilli. At 10-13 cm CVR length the uterine gland openings developed irregular folds and the maternal areolar cells showed numerous apical blebs. At 14-29 cm CVR length the foetal areolae showed a great increase in height at the expense of their width. At 30-34 cm (CVR) length the maternal areolae appeared discoid and sharply demarcated from the surrounding inter-areolar tissues and the foetal areolae were rounded to irregular in shape with well-developed areolar rims. The vascular casts showed a widely meshed capillary network on the maternal areola, connecting with the pre- and post-capillary vessels, whereas the foetal side showed a relatively dense capillary meshwork. These studies indicate that the areola in the placenta of the one-humped camel is of the regular type like in the pig, and is poorly vascularized.

This study aimed to elucidate development of the areola in the early dromedary placenta in comparison with that of the pig and mare. Placental tissues from 25 pregnant camels were obtained from Cairo abattoir and prepared for light, scanning and transmission electron microscopy by routine methods. Vascular casts were made by injection of 4 : 1 liquid plastic mixture of mercox and methylmethacrylate. Areolar formation was first observed at 4.5 cm curved-crown-rump CVR length, while by 5-9 cm CVR length, the endometrial surface was uneven and studded with numerous uterine gland openings, where corresponding foetal areolae were barely detectable and the foetal areolar cells were of variable appearance and covered with long microvilli. At 10-13 cm CVR length the uterine gland openings developed irregular folds and the maternal areolar cells showed numerous apical blebs. At 14-29 cm CVR length the foetal areolae showed a great increase in height at the expense of their width. At 30-34 cm (CVR) length the maternal areolae appeared discoid and sharply demarcated from the surrounding inter-areolar tissues and the foetal areolae were rounded to irregular in shape with well-developed areolar rims. The vascular casts showed a widely meshed capillary network on the maternal areola, connecting with the pre- and post-capillary vessels, whereas the foetal side showed a relatively dense capillary meshwork. These studies indicate that the areola in the placenta of the one-humped camel is of the regular type like in the pig, and is poorly vascularized.