Equine placentation.
Abstract: A tough, elastic glycoprotein capsule envelops the equine blastocyst between Days 6 and 23 after ovulation. It maintains the spherical configuration of, and provides physical support for, the embryo as it traverses the entire uterine lumen during Days 6-17, propelled by myometrial contractions that are stimulated by pulsatile release of prostaglandin F2alpha and prostaglandin E2. The capsule also accumulates constituents of the exocrine secretions of the endometrial glands ('uterine milk') as nutrients for the mobile embryo as it releases its antiluteolytic maternal recognition-of-pregnancy signal to the whole of the surface of the endometrium. Mobility ceases abruptly on Day 17 with a sudden increase in uterine tonicity that 'fixes' the conceptus at the base of one of the uterine horns. At Day 35, the trophoblast of the spherical conceptus has separated into its invasive and non-invasive components. The former, distinguished as the thickened, annulate chorionic girdle, invades the maternal endometrium to form the unique endometrial cups. These secrete a chorionic gonadotrophin that synergizes with pituitary follicle-stimulating hormone to induce secondary luteal development in the maternal ovaries. The cup cells express foreign fetal antigens that stimulate strong maternal humoral and cell-mediated immune responses, which curtail their lifespan. The non-invasive trophoblast of the allantochorion establishes a stable microvillous contact with the endometrial epithelium around Day 40 and, over the next 100 days, develops a complex multibranched interdigitation with the endometrium to form the microcotyledonary haemotrophic exchange units that cover the entire surface of the diffuse epitheliochorial placenta. Reduction in the effective total area of fetomaternal contact at this placental interface, by competition between twin conceptuses for the limited area of available endometrium, by attachment of the allantochorion to an imperfect endometrium in a mare with endometrosis, or following cross-breeding or embryo transfer between a sire and dam of dissimilar size, will all induce intrauterine growth retardation of the fetus and runting of the foal, which persists into adult life. Over 40 years ago, Professor Roger Short and his colleagues determined that the high concentrations of conventional and unique ring B unsaturated oestrogens in the blood and urine of mares during the second half of pregnancy stem from placental aromatization of large quantities of C-19 precursor molecules secreted by the temporarily hypertrophic fetal gonads. Placental production of progesterone and 5alpha-reduced progestagens, on the other hand, depends on both maternal and fetal adrenal sources of pregnenelone.
Publication Date: 2002-05-10 PubMed ID: 11999314DOI: 10.1071/rd01063Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Review
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
The research article essentially detailed the process of equine placentation, including the formation, function, and influences on the development of the equine placenta and its impact on fetal development and growth.
The role of the glycoprotein capsule
- The paper described that a strong, elastic glycoprotein capsule enwraps the equine blastocyst, which includes the embryo and its early amniotic cavity, during the period between Day 6 and 23 after ovulation.
- This capsule was seen to be vital for the embryo’s preservation, particularly when it traverses the full uterine lumen between Days 6 to 17.
- Its movements are powered by contractions in the muscular wall of the uterus, stimulated by the cyclical release of certain substances called prostaglandin F2alpha and prostaglandin E2.
- Furthermore, the capsule accumulates uterine milk, which provides nourishment for the mobile embryo once it starts to release a signal that prevents the destruction of the corpus luteum, necessary for maintaining the pregnancy.
Fixation and further separation of the trophoblast
- On Day 17, the embryo ceases to be mobile due to a sudden rise in uterine tonicity. This cements the conceptus at the base of a uterine horn.
- By Day 35, the covering of the growing embryo (the trophoblast) has been divided into invasive and non-invasive parts. The invasive part, the chorionic girdle, infiltrates the maternal endometrium forming unique endometrial cups.
- These cups release a special hormone which, together with follicle-stimulating hormone, induces the growth of the secondary corpus luteum necessary for the maintenance of the pregnancy.
- These cups also express antigens which trigger a maternal immune response that limits their lifespan.
Development of placental exchange units and related problems
- The non-invasive part of the trophoblast contacts with the endometrial epithelium by Day 40 and over the next 100 days, forms a complex network of contact points, forming the haemotrophic exchange units that cover the whole of the diffuse epitheliochorial placenta.
- The limited area of available endometrium for twinning, endometrosis, or when there is a significant difference in the size of the parents can all cause a reduction in the total area of contact, resulting in slowed intrauterine growth of the fetus and the stunting of the foal that can continue into adulthood.
- The increased estrogen levels in mares’ blood and urine during the second half of the pregnancy originates from placental transformation of large quantities of C-19 precursor molecules secreted by the temporarily hypertrophic fetal gonads.
- In contrast, the production of progesterone and other progestogens by the placenta requires both maternal and fetal adrenal sources of pregnenolone.
Cite This Article
APA
Allen WR, Stewart F.
(2002).
Equine placentation.
Reprod Fertil Dev, 13(7-8), 623-634.
https://doi.org/10.1071/rd01063 Publication
Researcher Affiliations
- University of Cambridge, Department of Clinical Veterinary Medicine Equine Fertility Unit, Mertoun Paddocks, Newmarket, Suffolk, UK.
MeSH Terms
- Allantois / anatomy & histology
- Animals
- Chorion / anatomy & histology
- Embryonic and Fetal Development
- Endometrium / anatomy & histology
- Endometrium / physiology
- Extraembryonic Membranes / anatomy & histology
- Extraembryonic Membranes / physiology
- Female
- Fetus / metabolism
- Gestational Age
- Horses / physiology
- Placenta / metabolism
- Placentation
- Pregnancy
- Steroids / biosynthesis
Citations
This article has been cited 26 times.- Gibson C, de Ruijter-Villani M, Stout TAE. Insulin-like growth factor system components expressed at the conceptus-maternal interface during the establishment of equine pregnancy. Front Vet Sci 2022;9:912721.
- Shen Y, Ren H, Davshilt T, Tian S, Wang X, Yi M, Ulaangerel T, Li B, Dugarjav M, Bou G. The transcriptome landscapes of allantochorion and vitelline-chorion in equine day 30 conceptus. Front Cell Dev Biol 2022;10:958205.
- Macleay CM, Carrick J, Shearer P, Begg A, Stewart M, Heller J, Chicken C, Brookes VJ. A Scoping Review of the Global Distribution of Causes and Syndromes Associated with Mid- to Late-Term Pregnancy Loss in Horses between 1960 and 2020. Vet Sci 2022 Apr 13;9(4).
- Rudolf Vegas A, Podico G, Canisso IF, Bollwein H, Almiñana C, Bauersachs S. Spatiotemporal endometrial transcriptome analysis revealed the luminal epithelium as key player during initial maternal recognition of pregnancy in the mare. Sci Rep 2021 Nov 16;11(1):22293.
- Parsons AM, Bouma GJ. A Potential Role and Contribution of Androgens in Placental Development and Pregnancy. Life (Basel) 2021 Jul 1;11(7).
- Gibson C, de Ruijter-Villani M, Bauersachs S, Stout TAE. Asynchronous Embryo Transfer Followed by Comparative Transcriptomic Analysis of Conceptus Membranes and Endometrium Identifies Processes Important to the Establishment of Equine Pregnancy. Int J Mol Sci 2020 Apr 7;21(7).
- Schöniger S, Schoon HA. The Healthy and Diseased Equine Endometrium: A Review of Morphological Features and Molecular Analyses. Animals (Basel) 2020 Apr 5;10(4).
- Klohonatz KM, Coleman SJ, Cameron AD, Hess AM, Reed KJ, Canovas A, Medrano JF, Islas-Trejo AD, Kalbfleisch T, Bouma GJ, Bruemmer JE. Non-Coding RNA Sequencing of Equine Endometrium During Maternal Recognition of Pregnancy. Genes (Basel) 2019 Oct 18;10(10).
- Klohonatz KM, Coleman SJ, Islas-Trejo AD, Medrano JF, Hess AM, Kalbfleisch T, Thomas MG, Bouma GJ, Bruemmer JE. Coding RNA Sequencing of Equine Endometrium during Maternal Recognition of Pregnancy. Genes (Basel) 2019 Sep 25;10(10).
- Klohonatz KM, Nulton LC, Hess AM, Bouma GJ, Bruemmer JE. The role of embryo contact and focal adhesions during maternal recognition of pregnancy. PLoS One 2019;14(3):e0213322.
- Moser G, Windsperger K, Pollheimer J, de Sousa Lopes SC, Huppertz B. Human trophoblast invasion: new and unexpected routes and functions. Histochem Cell Biol 2018 Oct;150(4):361-370.
- Haneda S, Nagaoka K, Nambo Y, Kikuchi M, Nakano Y, Li J, Matsui M, Miyake YI, Imakawa K. Expression of uterine lipocalin 2 and its receptor during early- to mid-pregnancy period in mares. J Reprod Dev 2017 Apr 21;63(2):127-133.
- Cohen L, Bousfield GR, Ben-Menahem D. The recombinant equine LHβ subunit combines divergent intracellular traits of human LHβ and CGβ subunits. Theriogenology 2015 Jun;83(9):1469-76.
- Tachibana Y, Sakurai T, Bai H, Shiota K, Nambo Y, Nagaoka K, Imakawa K. RNA-seq analysis of equine conceptus transcripts during embryo fixation and capsule disappearance. PLoS One 2014;9(12):e114414.
- Gambini A, De Stefano A, Bevacqua RJ, Karlanian F, Salamone DF. The aggregation of four reconstructed zygotes is the limit to improve the developmental competence of cloned equine embryos. PLoS One 2014;9(11):e110998.
- Cabrera-Sharp V, Read JE, Richardson S, Kowalski AA, Antczak DF, Cartwright JE, Mukherjee A, de Mestre AM. SMAD1/5 signaling in the early equine placenta regulates trophoblast differentiation and chorionic gonadotropin secretion. Endocrinology 2014 Aug;155(8):3054-64.
- Phillips KA, Bales KL, Capitanio JP, Conley A, Czoty PW, 't Hart BA, Hopkins WD, Hu SL, Miller LA, Nader MA, Nathanielsz PW, Rogers J, Shively CA, Voytko ML. Why primate models matter. Am J Primatol 2014 Sep;76(9):801-27.
- Sasaki M, Amano Y, Hayakawa D, Tsubota T, Ishikawa H, Mogoe T, Ohsumi S, Tetsuka M, Miyamoto A, Fukui Y, Budipitojo T, Kitamura N. Structure and steroidogenesis of the placenta in the Antarctic minke whale (Balaenoptera bonaerensis). J Reprod Dev 2013;59(2):159-67.
- Kammerer R, Zimmermann W. Coevolution of activating and inhibitory receptors within mammalian carcinoembryonic antigen families. BMC Biol 2010 Feb 4;8:12.
- de Mestre AM, Miller D, Roberson MS, Liford J, Chizmar LC, McLaughlin KE, Antczak DF. Glial cells missing homologue 1 is induced in differentiating equine chorionic girdle trophoblast cells. Biol Reprod 2009 Feb;80(2):227-34.
- Scoggin KE, Adlan F, Fedorka CE, Rakha SI, Stout TAE, Troedsson MHT, Ali HE. Gestation-Stage Related Changes in the IGF System Components in the Equine Placenta. Biomolecules 2025 Aug 6;15(8).
- Navarrete Zamora MB, Acuña F, Duarte da Silva M, Santos-Silva T, Garcia MHH, Barreto RDSN, Sato Sato A, Barbeito CG, Miglino MA. Morphology and Immunoexpression of Selenoproteins in Term Placenta of Alpaca (Vicugna pacos) from the Peruvian Andes. Biology (Basel) 2025 Jan 14;14(1).
- Piotrowska-Tomala KK, Jonczyk AW, Szóstek-Mioduchowska A, Hojo T, Żebrowska E, Katila T, Ferreira-Dias G, Skarzynski DJ. Intrauterine devices influence prostaglandin secretion by equine uterus: in vitro and in vivo studies. BMC Vet Res 2024 Feb 3;20(1):46.
- Oda K, Yoshida M, Irshad AR, Kanazawa T, Takahashi T. Development of a fluorometric Cuboni test for the semi-quantitative measurement of urinary estrogen levels and pregnancy detection in mares. J Reprod Dev 2024 Feb 19;70(1):25-29.
- Hao K, Wang J, Yu H, Chen L, Zeng W, Wang Z, Hu G. Peroxisome Proliferator-Activated Receptor γ Regulates Lipid Metabolism in Sheep Trophoblast Cells through mTOR Pathway-Mediated Autophagy. PPAR Res 2023;2023:6422804.
- Thompson RE, Meyers MA, Palmer J, Veeramachaneni DNR, Magee C, de Mestre AM, Antczak DF, Hollinshead FK. Production of Mare Chorionic Girdle Organoids That Secrete Equine Chorionic Gonadotropin. Int J Mol Sci 2023 May 31;24(11).
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
