Embryonic loss in mares. Incidence, possible causes, and diagnostic considerations.
Abstract: Fertilization rates were similar for normal and subfertile mares, and much of the difference in fertility between normal and subfertile mares was due to embryonic loss. Fertilization rate estimates for mares ranged from 71 to 96 per cent. The incidence of embryonic loss detected by ultrasonography between Days 11 and 50 was approximately 9 per cent for normal mares, and the estimated incidence of embryonic loss before Day 14 was also 9 per cent. Therefore, the estimated incidence of embryonic loss in normal mares between fertilization and Day 50 is approximately 18 per cent (Fig. 1). In subfertile mares, the corresponding estimate for embryonic loss between fertilization and Day 50 is 80 per cent, with most embryonic losses occurring before Day 14 in subfertile mares (Fig. 1). The high rate of early embryonic loss in subfertile mares could be related to embryonic defects, oviductal environment, or uterine environment. Oviductal embryos from subfertile mares were less viable than embryos from normal mares; therefore, embryonic defects were important in early embryonic losses in subfertile mares. These defects might be inherent within the embryo or might arise from the early oviductal environment. The uterine environment of subfertile mares was adequate to support normal embryos in early gestation; however, the relationship between the uterine environment and the increased metabolic demands of the conceptus in the late embryonic or early fetal periods requires further study. The uterine environment is also altered in mares with endometritis; therefore, endometritis may also be an important factor in embryonic loss in some mares. Uterine-induced luteolysis, as well as the effect of the pathogen or the resulting inflammation, may lead to embryonic loss. An increased susceptibility of some subfertile mares to endometritis could result in embryonic loss secondary to a postcoital endometritis that persists until the embryo reaches the uterus at Days 5 or 6 postovulation. Although progesterone is critical to embryonic survival, the cause-and-effect relationship between progesterone and spontaneous embryonic loss remains unclear. Reduced progesterone concentrations could be related to endometritis, failure of maternal pregnancy recognition, or luteal insufficiency. Progesterone supplementation may be indicated for some mares, but the value of exogenous progesterone for prevention of spontaneous embryonic loss has not been critically tested. A number of other factors have been associated with embryonic loss in mares.(ABSTRACT TRUNCATED AT 400 WORDS)
Publication Date: 1988-08-01 PubMed ID: 3044540DOI: 10.1016/s0749-0739(17)30641-7Google 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.
This research investigates the causes of embryonic loss in horses, highlighting that fertilization rates are similar in both healthy and subfertile mares, with the primary difference in fertility due to embryonic loss. The study found that such losses could be due to embryonic defects, the environment of the oviduct, or the uterine environment.
Embryonic Loss and Fertility Rates in Mares
- The research starts by establishing that fertilization rates are similar in both healthy and subfertile mares, with approximately 71% to 96% of mares achieving fertilization.
- It’s noted that the major difference in fertility seems to be due to embryonic loss rate, wherein normal mares experience an estimated 18% loss in embryos between fertilization and Day 50 of pregnancy, whereas subfertile mares showed a remarkable estimated loss of 80% in the same period.
- The majority of the embryonic losses in subfertile mares occur before Day 14 of pregnancy.
Probable Causes of Embryonic Loss
- The study proposes three possible primary causes—embryonic defects, unfavorable oviductal environment, and adverse uterine environment.
- Subfertile mares showed less viable oviductal embryos than normal mares, indicating that embryonic defects play a crucial role in early pregnancy loss, particularly in subfertile mares.
- These defects could potentially be inherent within the embryo or arise due to an unfavorable early oviductal environment.
The Role of Uterine Environment
- Notably, the uterine environment of the subfertile mares was enough to shelter normal embryos during the early gestation period, but the researchers suggest that the relation between the uterine environment and the increased metabolic requirements of a conceptus during the late embryonic or early fetal periods requires additional analysis.
- Mares suffering from endometritis (inflammation of the uterine lining) could experience an altered uterine environment, which possibly constitutes an essential factor in embryonic loss.
Progesterone and Endometritis
- The research suggests a complicated relationship between the hormone progesterone, necessary for embryonic survival, and embryonic loss, with the exact cause-and-effect relationship still unclear.
- Reduced levels of progesterone might be connected to endometritis, failure of recognizing pregnancy by the mare (maternal pregnancy recognition), or luteal deficiency (a possible abnormality in the ovulating corpus luteum).
- While some mares could potentially benefit from progesterone supplementation, the research urges the need for further study, as the benefits of exogenous progesterone for the prevention of spontaneous embryonic loss are yet unproven.
Cite This Article
APA
Ball BA.
(1988).
Embryonic loss in mares. Incidence, possible causes, and diagnostic considerations.
Vet Clin North Am Equine Pract, 4(2), 263-290.
https://doi.org/10.1016/s0749-0739(17)30641-7 Publication
Researcher Affiliations
- Department of Clinical Sciences, New York State College of Veterinary Medicine, Cornell University, Ithaca.
MeSH Terms
- Animals
- Female
- Fetal Death / veterinary
- Fetal Resorption / diagnosis
- Fetal Resorption / epidemiology
- Fetal Resorption / etiology
- Fetal Resorption / veterinary
- Horse Diseases / diagnosis
- Horse Diseases / epidemiology
- Horse Diseases / etiology
- Horses
- Pregnancy
- Ultrasonography / veterinary
References
This article includes 162 references
Citations
This article has been cited 5 times.- Beckers KF, Liu CC, Gomes VCL, Schulz CJ, Childers GW, Fedorka CE, Sones JL. Effects of Intra-uterine Ceftiofur on the Equine Uterine Microbiome. Vet Sci 2025 Aug 30;12(9).
- Siemieniuch-Tartanus M. The early pregnancy in mares - What do we still not know?. Vet Anim Sci 2025 Jun;28:100441.
- Antczak DF, Allen WRT. Placentation in Equids. Adv Anat Embryol Cell Biol 2021;234:91-128.
- Falomo ME, Del Re B, Rossi M, Giaretta E, Da Dalt L, Gabai G. Relationship between postpartum uterine involution and biomarkers of inflammation and oxidative stress in clinically healthy mares (Equus caballus). Heliyon 2020 Apr;6(4):e03691.
- Boakari YL, Ali HE, Dini P, Loux S, Fernandes CB, Scoggin K, Esteller-Vico A, Lawrence L, Ball B. A High Protein Model Alters the Endometrial Transcriptome of Mares. Genes (Basel) 2019 Jul 30;10(8).
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
