Fetomaternal interactions and influences during equine pregnancy.
Abstract: The equine embryo takes 6 days to traverse the oviduct and, when it finally enters the uterus, it remains spherical in shape and moves continually throughout the uterine lumen until day 17 after ovulation to deliver its maternal recognition of pregnancy signal to the entire endometrium. Between day 25 and day 35 after ovulation, the trophoblast cells of a discrete annulate portion of the chorion multiply rapidly and acquire an invasive phenotype and, between day 36 and day 38, migrate deeply into the maternal endometrium to form the equine-unique endometrial protuberances known as endometrial cups. These cups secrete large quantities of a gonadotrophic hormone (eCG) into the maternal circulation which, in conjunction with pituitary FSH, stimulates the development of accessory luteal structures in the maternal ovaries to supplement the supply of progesterone to maintain the pregnancy until the placenta can assume this role at about day 100. The non-invasive allantochorion extends slowly to fill the uterus by days 80-85 and its microcotyledonary architecture, which provides both haemotrophic and histotrophic nutrition for the growing fetus, is not fully established until days 120-140. The fetoplacental unit synthesizes large quantities of steroid hormones during the second half of pregnancy, using fetal C-19 precursors secreted by the enlarged fetal gonads for the production of oestrogens and maternal C-21 precursors for the synthesis of progesterone and large quantities of 5alpha-reduced progestagens. Near term, additional pregnenelone is secreted by the fetal adrenal glands so that the mare exhibits the unusual phenomenon of foaling while maternal serum progestagen concentrations are increasing and oestrogen concentrations are decreasing.
Publication Date: 2001-03-30 PubMed ID: 11277870
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.
This study explores the interactions between a fetus and mother horse during pregnancy and how these influence the development of the embryo and maintenance of the pregnancy. The research dives into the journey of the embryo, from its movement in the uterus to the various hormones it secretes to signal its presence and maintain a healthy pregnancy.
Embryo Development and Journey
- The study begins by explaining the journey of the equine embryo. It takes about 6 days for it to traverse the oviduct. Once it enters the uterus, it remains spherical and moves constantly within the uterine lumen.
- Until around day 17 after ovulation, it continually delivers its maternal recognition of pregnancy signal to the endometrium, the lining of the uterus.
Trophoblast Cell Development and Role
- Between days 25 and 35 after ovulation, trophoblast cells, which forms the outer layer of a blastocyst providing nutrients to the embryo and develops into a large part of the placenta, in a portion of the chorion (the outermost fetal membrane) begins to multiply and morphs into an invasive phenotype.
- Between days 36 and 38, these cells migrate deeply into the maternal endometrium, forming unique endometrial protuberances called endometrial cups.
Formation of Endometrial Cups
- Endometrial cups secrete a large amount of a hormone called eCG into the mother’s bloodstream. In conjunction with another hormone known as pituitary FSH, this aids in the development of additional luteal structures in the maternal ovaries. This supplements the supply of progesterone, a hormone necessary for maintaining pregnancy, until about day 100 when the placenta can assume this role.
Role of the Allantochorion
- The allantochorion, which is a non-invasive part, extends slowly to fill the uterus by days 80-85. It has a microcotyledonary architecture, providing both haemotrophic (bloodborne) and histotrophic (derived from maternal tissues) nutrition for the growing fetus.
- This complex structural development is not fully established until days 120-140.
Circulation of Steroid Hormones
- In the second half of pregnancy, there’s synthesis of a large quantity of steroid hormones using fetal and maternal precursors for the production of oestrogens and progestogens.
- As the term nears, the fetal adrenal glands secrete additional pregnenelone. Hence, the mother horse experiences increasing maternal serum progestagen concentrations and decreasing oestrogen concentrations while giving birth.
Cite This Article
APA
Allen WR.
(2001).
Fetomaternal interactions and influences during equine pregnancy.
Reproduction, 121(4), 513-527.
Publication
Researcher Affiliations
- Thoroughbred Breeders' Association, Equine Fertility Unit, Mertoun Paddocks, Woodditton Road, Newmarket, Suffolk CB8 9BH, UK.
MeSH Terms
- Animals
- Embryo Transfer / veterinary
- Embryonic and Fetal Development
- Endometrium / physiology
- Extraembryonic Membranes / physiology
- Female
- Fetus / physiology
- Gestational Age
- Gonads / embryology
- Horses / physiology
- Placentation
- Pregnancy
- Pregnancy, Animal / physiology
Citations
This article has been cited 23 times.- Meuffels-Barkas J, Wilsher S, Allen WRT, Ververs C, Lueders I. Comparative reproduction of the female horse, elephant and rhinoceros: implications for advancing Assisted Reproductive Technologies (ART). Reprod Fertil 2023 Jul 1;4(3).
- Schuler G, Fürbass R, Klisch K. Placental contribution to the endocrinology of gestation and parturition. Anim Reprod 2018 Jul-Sep;15(Suppl 1):822-842.
- 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.
- Gao Y, Hannan MA, Murata K, Rajabi-Toustani R, Nambo Y. Ultrasonographic examination of equine fetal growth parameters throughout gestation in pony for Equine-Assisted Therapy. J Vet Med Sci 2022 Jan 7;84(1):74-81.
- Scarlet D, Handschuh S, Reichart U, Podico G, Ellerbrock RE, Demyda-Peyrás S, Canisso IF, Walter I, Aurich C. Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus. Animals (Basel) 2021 Aug 17;11(8).
- Stefanetti V, Pascucci L, Wilsher S, Cappelli K, Capomaccio S, Reale L, Passamonti F, Coletti M, Crociati M, Monaci M, Marenzoni ML. Differential Expression Pattern of Retroviral Envelope Gene in the Equine Placenta. Front Vet Sci 2021;8:693416.
- Smits K, Gansemans Y, Tilleman L, Van Nieuwerburgh F, Van De Velde M, Gerits I, Ververs C, Roels K, Govaere J, Peelman L, Deforce D, Van Soom A. Maternal Recognition of Pregnancy in the Horse: Are MicroRNAs the Secret Messengers?. Int J Mol Sci 2020 Jan 9;21(2).
- Kimura Y, Sasaki M, Watanabe K, Dhakal P, Sato F, Taya K, Nambo Y. Expression of activin receptors in the equine uteroplacental tissue: an immunohistochemical analysis. J Equine Sci 2018;29(2):33-37.
- Smits K, Willems S, Van Steendam K, Van De Velde M, De Lange V, Ververs C, Roels K, Govaere J, Van Nieuwerburgh F, Peelman L, Deforce D, Van Soom A. Proteins involved in embryo-maternal interaction around the signalling of maternal recognition of pregnancy in the horse. Sci Rep 2018 Mar 27;8(1):5249.
- Park JJ, Seong HK, Kim JS, Munkhzaya B, Kang MH, Min KS. Internalization of Rat FSH and LH/CG Receptors by rec-eCG in CHO-K1 Cells. Dev Reprod 2017 Jun;21(2):111-120.
- Stefanetti V, Marenzoni ML, Passamonti F, Cappelli K, Garcia-Etxebarria K, Coletti M, Capomaccio S. High Expression of Endogenous Retroviral Envelope Gene in the Equine Fetal Part of the Placenta. PLoS One 2016;11(5):e0155603.
- Aurich C, Budik S. Early pregnancy in the horse revisited - does exception prove the rule?. J Anim Sci Biotechnol 2015;6:50.
- Ono M, Akuzawa H, Nambo Y, Hirano Y, Kimura J, Takemoto S, Nakamura S, Yokota H, Himeno R, Higuchi T, Ohtaki T, Tsumagari S. Analysis of the equine ovarian structure during the first twelve months of life by three-dimensional internal structure microscopy. J Vet Med Sci 2016 Jan;77(12):1599-603.
- 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.
- Brekke TD, Good JM. Parent-of-origin growth effects and the evolution of hybrid inviability in dwarf hamsters. Evolution 2014 Nov;68(11):3134-48.
- Lueders I, Niemuller C, Rich P, Gray C, Hermes R, Goeritz F, Hildebrandt TB. Gestating for 22 months: luteal development and pregnancy maintenance in elephants. Proc Biol Sci 2012 Sep 22;279(1743):3687-96.
- Bartošová J, Komárková M, Dubcová J, Bartoš L, Pluháček J. Concurrent lactation and pregnancy: pregnant domestic horse mares do not increase mother-offspring conflict during intensive lactation. PLoS One 2011;6(8):e22068.
- Satué K, La Fauci D, Medica P, Damiá Gímenez E, Cravana C, Fazio E. Shifts between pro-inflammatory and anti-inflammatory profiles in pregnant mares: a review of physiological functions. Front Vet Sci 2025;12:1660759.
- Siemieniuch-Tartanus M. The early pregnancy in mares - What do we still not know?. Vet Anim Sci 2025 Jun;28:100441.
- Ulaangerel T, Mu S, Sodyelalt J, Yi M, Zhao B, Hao A, Wen X, Han B, Bou G. Transcriptome Analysis Reveals Equine Endometrium's Gene Expression Profile Around Embryo Fixation. Genes (Basel) 2025 Feb 1;16(2).
- Cuccato M, Bertuglia A, Divari S, Brambilla E, Grieco V, Bollo E, Scaglione FE. Case report: Findings in ovaries development from an aborted equine fetus. Front Vet Sci 2024;11:1275220.
- 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.
- Carter AM. Evolution of Placental Hormones: Implications for Animal Models. Front Endocrinol (Lausanne) 2022;13:891927.
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
