Comparative morphological analysis of the placenta of mares in late pregnancy by histomorphometry

Histomorphometric examination of the placenta of mares in the final stages of gestation revealed statistically significant differences in morphometric parameters during the physiological and pathological course of pregnancy. The area of the chorioallantois (cm2), the thickness of the chorion and allantoamnion (mm), the density of villi per unit area (villi/cm2) and per unit surface of the chorion, as well as the diameter and number of vessels in the allantoamnion per area of 100 cm2 were quantified. The analysis showed that placental insufficiency, manifested in the form of premature birth, placentitis and retention of the afterbirth, is associated with the disorganization of cellular structures, characterized by their sparse arrangement in the form of small, distant clusters. In contrast, the formation of denser and more coherent cell clusters is observed in mares with physiological pregnancy. Histomorphometry of the cellular structures of the fetal part of the placenta, in particular, the topological metrics of the network, acts as the main discriminating factor that makes it possible to quantify the specific features of the placenta of mares in conditions of pathological conditions. The distribution of chorioallantois villi over the entire surface of the placenta and the absence of dense contacts with the glandular epithelium of the uterus form microcotyledons, which determines the classification of the placenta of mares as diffuse microcotyledonous epitheliochoric. There is marked vascularization of all components of the placenta, including the amniotic membrane, stem and terminal villi of the chorioallantois. The stromal part of the placenta, represented by the amniotic membrane and chorioallantois villi, consists mainly of collagen fibers. The presence of long stem villi in certain areas of the placenta (distal part, middle of the contralateral horn, dividing line of the horns, middle of the main horn) correlates with their spatial location in the uterus, providing optimal contact with the uterine glands for effective gas exchange and nutritional support of the fetus.

1. Morphogenesis of the placenta in cattle with eclampsia / Prikhodko S. A., Rodin P. V., Avdeenko V. S., Plemyashov K. V. // Issues of regulatory and legal regulation in veterinary medicine. 2020, No. 1, pp. 117-121.

2. Saenko N. V. Morphology of provisional organs of a horse in relationship with the viability of newborn foals: Bulletin of the Krasnoyarsk State Agrarian University, No. 7, 2024 / - pp. 143-151.

3. Rodin P. V., Avdeenko V. S. Histological changes in the placenta of cattle with gestosis. // Issues of regulatory and legal regulation in veterinary medicine, 2015, 2: 233-235.

4. Kristoforova B.V., Saenko N.V. Provisional organs and viability of newborn animals: Monograph. SPb., 2022. - 158 p.

5. Teixeira A.R., Leao M.T., Costa A.L., Martin S., Abreu P., Blibernicht M. et al. Biometric and weight assessment of newborn foals: the influence of maternal factors. Abstract from the collection of abstracts of the 71st annual Virtual Meeting of the European Livestock Federation, December 1-4. Wageningen: Wageningen Academic Publishers (2020), 469 pp.

6. El-Sheikh Ali H., Legacki E.L., Loux S.C., Esteller-Vico A., Dini P., Scoggin K.E., Conley A.J., Stanley S.D., Ball B.A. Equine placentitis is associated with a downregulation in myometrial progestin signaling. Biol Reprod 2019; 101:162-176.

7. Neto da Silva A. K., Costa A. L., Teixeira A., Alpoim-Moreira J., Fernandes K., Fradinho M. J., Rebordan M. R., Silva E., Ferreira da Silva J., Blibernicht M., Alexander-Pires G., Ferreira-Diaz G. Collagen and microvascular network in placentas of young and old mares. Front Vet Sci. 2022 Jan 4; 8:772658.

8. Wynn M.A., Ball B.A., May J., EstellerVico A., Canisso I, Squires E., Troedsson M. Changes in maternal pregnane concentrations in mares with experimentally-induced, ascending placentitis. Theriogenology 2018; 122:130-136.

9. Park Y.S., Kim S., Park D.G., Kim D.H., Yoon K.W., Shin W., Han K. Comparison of library construction kits for mRNA sequencing in the Illumina platform. Genes Genomics 2019; 41:1233-1240.

10. El-Sheikh Ali H., Boakari Y.L., Loux S.C., Dini P., Scoggin K.E., Esteller-Vico A., Kalbfleisch T., Ball B.A. Transcriptomic analysis reveals the key regulators and molecular mechanisms underlying myometrial activation during equine placentitis. Biology of Reproduction 2020; 102:1306–1325.

11. Mu S., Shen Yu., Ren H., Ulaangerel T., Yi M., Zhao B., Hao A., Liu C., Wen S., Dugarzhav M., Bow G. Effect of interleukin- 6 (IL-6) on in vitro cultured foal chorion cells. Animals. 2025. 15(3):450.

12. Antczak D.F., Allen W.R.T. Placement in ungulates. Adv Anat Embryol Cell Biol. 2021; 234:91-128. doi: 10.1007/978-3-030-77360-1_6.

13. Citation: Neto da Silva AC, Costa AL, Teixeira A, Alpoim-Moreira J, Fernandes C, Fradinho MJ, Rebordão MR, Silva E, Ferreira da Silva J, Bliebernicht M, AlexandrePires G and Ferreira-Dias G (2022) Collagen and Microvascularization in Placentas from Young and Old Mares. Vet. Sci. 8:772658. doi: 10.3389/fvets.2021.772658.

14. The adaptive potential of newborn caves under conditions of technogenic anthropobio -cenosis / N. Saenko [et al.] // E3S Web of Conferences. 2021. No. 265.

15. Canisso I.F., Luks S.K., Lima F.S. Biomarkers of placental diseases in mares. Theriogenology. 2020 1; 150:302-307.

16. The adaptive potential of newborn caves under conditions of technogenic anthropobio -cenosis / N. Saenko [et al.] // E3S Web of Conferences. 2021. No. 265.