Early pregnancy in the horse revisited – does exception prove the rule?
Abstract: Early equine pregnancy shares many features with that of more intensively assessed domestic animals species, but there are also characteristic differences. Some of those are poorly understood. Descent of the equine conceptus into the uterine lumen occurs at day 5 to 6 after ovulation but is only possible when the embryo secretes prostaglandin E2. Although maintenance of equine pregnancy probably involves secretion of a conceptus derived anti-luteolytic factor, this agent has not been identified. Rapid growth, conceptus mobility and presence of an acellular capsule at the time of maternal recognition of pregnancy, i.e. between days 12 and 14, are prerequisites to avoid pregnancy loss. Progesterone together with 5α-pregnanes is secreted by the corpus luteum and induces the production of endometrial histotroph which is responsible for conceptus nutrition until placention. A stable contact between the outer trophoblast layer of the allantochorion and the luminal epithelium of the endometrium is not established before days 40 to 42 of pregnancy.
Publication Date: 2015-12-02 PubMed ID: 26635959PubMed Central: PMC4668677DOI: 10.1186/s40104-015-0048-6Google Scholar: Lookup
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Summary
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This study reviews the unique aspects of early pregnancy in horses, focusing on how it compares to other domestic animals and highlighting the current gaps in knowledge. Certain characteristics, such as the embryo’s release into the uterus, its growth and mobility, and how it is protected and nourished, are detailed.
Overview of Equine Pregnancy
- Equine pregnancy exhibits some similar characteristics to other domestic animals, but also possesses unique elements. Understanding these differences is crucial for effective veterinary care and improving reproductive success in horses.
- The descent of the horse embryo into the uterus occurs around 5 to 6 days post ovulation, and this process is facilitated by the secretion of a hormone known as prostaglandin E2. Currently, the reasons as to why horses specifically require the secretion of this hormone for successful embryo descent are still relatively unknown.
Conceptus Derived Anti-luteolytic Factor (CDALF) and Pregnancy Maintenance
- While it is theorized that the maintenance of equine pregnancy involves a component emitted by the embryo (known as a conceptus-derived anti-luteolytic factor, or CDALF), the exact nature of this agent remains unidentified. Figuring out what this component is could greatly contribute to our understanding of horse pregnancy and potentially be used to help maintain pregnancies in difficult cases.
Importance of Growth, Mobility, and the Acellular Capsule
- Between days 12 and 14 of equine pregnancy, rapid embryonic growth, active movement of the conceptus (embryo and surrounding membranes), and the presence of an acellular capsule are crucial for the maternal recognition of pregnancy.
- An insufficiency in any of these aspects might lead to pregnancy loss, emphasising their critical role in the initial stages.
Role of Progesterone and 5α-pregnanes
- The hormones progesterone and 5α-pregnanes are secreted by the corpus luteum (a temporary endocrine structure involved in ovulation and early pregnancy stages). These hormones stimulate the endometrial lining of the uterus to produce a substance known as histotroph, which is accountable for nourishing the conceptus before the formation of the placenta.
Establishment of Stable Contact
- Direct contact between the outer trophoblast layer of the allantochorion (a membrane formed during pregnancy) and the luminal epithelium of the endometrium does not occur until around days 40 to 42 of pregnancy. This indicates a delayed attachment in horses compared to other domestic animals, which may have significant implications for horse reproductive health and management.
Cite This Article
APA
Aurich C, Budik S.
(2015).
Early pregnancy in the horse revisited – does exception prove the rule?
J Anim Sci Biotechnol, 6, 50.
https://doi.org/10.1186/s40104-015-0048-6 Publication
Researcher Affiliations
- Artificial Insemination and Embryo Transfer, Vetmeduni Vienna, Veterinärplatz 1, 1210 Vienna, Austria.
- Artificial Insemination and Embryo Transfer, Vetmeduni Vienna, Veterinärplatz 1, 1210 Vienna, Austria.
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