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Home / Equine Research Bank / Placenta / A review of implantation and early placentation in the mare.
Placenta2009; 30(12); 1005-1015; doi: 10.1016/j.placenta.2009.09.007

A review of implantation and early placentation in the mare.

Abstract: Constant, self induced mobility throughout the uterine lumen between days 6 and 17 after ovulation, complete envelopment by a self-secreted glycoprotein capsule between days 7 and 30 and 'injection' of specialised, gonadotrophin-secreting trophoblast cells into the maternal endometrium at days 35-37 are three unusual aspects of equine embryogenesis. The outer trophoblast layer of the allantochorion finally establishes a stable, microvillous contact with the lumenal epithelium of the endometrium around days 40-42 and placentation commences thereafter. The allantochorion elongates steadily until it occupies the whole of the interior of the uterus by day 85. It develops branched, sub-branched and highly convoluted microcotyledons over its entire surface and these interdigitate closely with accommodating endometrial upgrowths (sulci) to provide a total microscopic area of fetomaternal contact for haemotrophic exchange which exceeds 50m(2) at term. Endometrial gland exocrine secretions, imbibed by elongated trophoblast cells that form areolae above the mouths of the endometrial glands, contribute histotrophic nutrients to the fetus throughout gestation. These dual forms of haemotrophic and histotrophic nutrition achieve a high degree of precocity in the foal at birth. This paper describes the gross and microscopic changes at the fetomaternal interface between days 20 and 80 of gestation in the pregnant mare which establishes the extensive, diffuse, non-invasive microcotyledonary placenta that supports fetal growth and development thereafter.
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Publication Date: 2009-10-22 PubMed ID: 19850339DOI: 10.1016/j.placenta.2009.09.007Google Scholar: Lookup
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Summary

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This research article examines the unique aspects of equine embryo development and early placentation in mares, detailing the intricate process by which the equine fetus receives nutrition and attains a high degree of maturity at birth.

Introduction to Early Horse Embryogenesis and Placentation

  • The study first explores the unique aspects of embryogenesis in horses. It mentions three specific unusual characteristics: self-induced mobility within the uterus between the 6th and 17th day post-ovulation, encoding in a self-secreted glycoprotein capsule from the 7th to 30th day, and the injection of specialized trophoblast cells into the endometrium on the 35th to 37th day.

Establishment of Stable Contact and Placentation

  • By the 40th to 42nd day marks the moment when the outer trophoblast layer makes a stable, minuscule and finger-like contact with the endometrium’s innermost layer, starting the process of placentation.

Development and Expansion of the Allantochorion

  • The allantochorion – the fetal portion of the placenta – keeps expanding until the 85th day post conception when it fully occupies the interior of the uterus. This development includes the formation of branched, sub-branched, and highly convoluted microcotyledons across the entire allantochorion surface. The microcotyledons closely interdigitate with endometrial upgrowths to provide a large microscopic area for fetomaternal contact for nutrient exchange.

Dual Forms of Foetal Nutrition

  • The areolae, elongated trophoblast cells, imbibe secretion from endometrial glands thus contributing to the nutrition of the fetus throughout gestation. This study highlights the dual processes of blood nourishment (haemotrophic) and nutrient uptake via secretions (histotrophic) resources, which contribute to the foal’s precocity at birth.

Microscopic Changes at the Fetomaternal Interface

  • The research delves into the minute changes that take place between day 20 and 80 of gestation at the fetus-mother interface in pregnant mares. This progressive process solidifies the formation of the non-invasive, extensive, and diffuse microcotyledonary placenta that supports development and growth of the fetus thereafter.

Cite This Article

APA
Allen WR, Wilsher S. (2009). A review of implantation and early placentation in the mare. Placenta, 30(12), 1005-1015. https://doi.org/10.1016/j.placenta.2009.09.007

Publication

Placenta
ISSN: 1532-3102
NlmUniqueID: 8006349
Country: Netherlands
Language: English
Volume: 30
Issue: 12
Pages: 1005-1015

Researcher Affiliations

Allen, W R
  • The Paul Mellon Laboratory of Equine Reproduction, 3 Tower Stables, Suffolk, UK. paulmellonlab@btconnect.com
Wilsher, S

    MeSH Terms

    • Animals
    • Embryo Implantation / physiology
    • Embryo, Mammalian / anatomy & histology
    • Embryo, Mammalian / embryology
    • Female
    • Horses / physiology
    • Placenta / anatomy & histology
    • Placenta / embryology
    • Placentation / physiology
    • Pregnancy

    Citations

    This article has been cited 16 times.
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