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Reproduction (Cambridge, England)2001; 121(4); 513-527;

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.
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Publication Date: 2001-03-30 PubMed ID: 11277870
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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

Reproduction (Cambridge, England)
ISSN: 1470-1626
NlmUniqueID: 100966036
Country: England
Language: English
Volume: 121
Issue: 4
Pages: 513-527

Researcher Affiliations

Allen, W R
  • 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.
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