Equine Abortion in Horses: A Silent Threat to Breeding Success

Equine Abortion in Horses: A Silent Threat to Breeding Success 

Reproductive failure is one of the biggest challenges in the equine industry, and abortion in mares remains a major cause of economic loss worldwide. Defined as pregnancy loss before 300 days of gestation, equine abortion can disrupt breeding programs, reduce foal output, and impact the long-term value of mares and stallions^1,2,3,4. 

Why Equine Abortion Matters 

A single abortion can mean more than just the loss of a foal. It can lead to¹: 

• Financial losses for breeders 

• Reduced reproductive efficiency 

• Increased veterinary expenses 

• Delays in breeding schedules 

• Risk of disease spread within the stable 

Early recognition and preventive care are therefore critical in equine practice. 

Viral Infections: The Leading Concern 

Several viral diseases are strongly linked to abortion in mares. 

Equine Herpesvirus (EHV-1) 

One of the most common infectious causes of abortion, EHV-1 can also cause respiratory and neurological disease in horses^6,7,8. The virus spreads rapidly through nasal secretions, contaminated equipment, and close contact. 

Equine Arteritis Virus (EAV) 

EAV affects the respiratory and reproductive systems and may lead to fetal death and abortion. Stallions can act as carriers, transmitting the virus during breeding^1,9,10,11,12. 

Other Viral Threats 

Viruses such as Equine Infectious Anemia Virus (EIAV) and West Nile Virus (WNV) have also been associated with reproductive losses in horses¹. 

Bacterial Causes of Abortion 

Bacterial infections can trigger placentitis, fetal infection, and late-term abortion. 

Important bacterial pathogens include: 

• Salmonella abortus equi 

• Streptococcus zooepidemicus 

• Escherichia coli 

• Rhodococcus equi 

• Leptospira species^1,13 

These infections often spread through contaminated water, feed, bedding, or direct animal contact. 

Fungal and Parasitic Risks 

Fungal placentitis, especially caused by Aspergillus species, is another important cause of abortion in mares¹. 

Parasitic diseases such as neosporosis and equine piroplasmosis have also been linked with pregnancy loss and poor reproductive outcomes¹. 

Non-Infectious Factors Also Play a Role 

Not all abortions are caused by infections. Other important causes include: 

• Twinning 

• Umbilical cord torsion 

• Hormonal imbalances 

• Toxicosis 

• Poor management practices¹ 

Proper nutrition, stress reduction, and regular reproductive monitoring are essential for maintaining pregnancy health. 

Prevention Is the Key 

Reducing abortion risk in horses requires a proactive approach, including: 

• Routine vaccination 

• Strict biosecurity measures 

• Early disease diagnosis 

• Vector and insect control 

• Regular reproductive examinations 

• Isolation of infected animals 

Modern diagnostic tools such as PCR and serological testing help veterinarians identify infectious causes quickly and improve herd management outcomes. 

Final Takeaway 

Equine abortion remains a significant reproductive and economic challenge in horse breeding. From viral outbreaks to bacterial infections and management-related factors, multiple risks can threaten a healthy pregnancy. Early detection, preventive healthcare, and strong biosecurity practices remain the best defense against pregnancy loss in mares. 

References 

1. Li L, Li S, Ma H, Akhtar MF, Tan Y, Wang T, Liu W, Khan A, Khan MZ, Wang C. An overview of infectious and non-infectious causes of pregnancy losses in equine. Animals. 2024 Jul 2;14(13):1961. https://doi.org/10.3390/ani14131961  

2. Ali AA, Abdallah F, Shemies OA, Kotb G, Nafea MR. Molecular characterization of equine herpes viruses type 1 and 4 among Arabian horse populations in Egypt during the period between 2021 and 2022. Open Veterinary Journal. 2024 Jan 31;14(1):534. https://pmc.ncbi.nlm.nih.gov/articles/PMC11018441/pdf/OpenVetJ-14-534.pdf  

3. Cantón GJ, Navarro MA, Asin J, Chu P, Henderson EE, Mete A, Uzal FA. Equine abortion and stillbirth in California: a review of 1,774 cases received at a diagnostic laboratory, 1990–2022. Journal of Veterinary Diagnostic Investigation. 2023 Mar;35(2):153-62. https://journals.sagepub.com/doi/pdf/10.1177/10406387231152788  

4. Macleay CM, Carrick J, Shearer P, Begg A, Stewart M, Heller J, Chicken C, Brookes VJ. A scoping review of the global distribution of causes and syndromes associated with mid-to late-term pregnancy loss in horses between 1960 and 2020. Veterinary Sciences. 2022 Apr 13;9(4):186. https://www.mdpi.com/2306-7381/9/4/186  

5. Chen L, Li S, Li W, Yu Y, Sun Q, Chen W, Zhou H, Wang C, Li L, Xu M, Khan MZ. Rutin prevents EqHV-8 induced infection and oxidative stress via Nrf2/HO-1 signaling pathway. Frontiers in Cellular and Infection Microbiology. 2024 Apr 25;14:1386462. https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2024.1386462/full  

6. Wang T, Li S, Hu X, Geng Y, Chen L, Liu W, Zhao J, Tian W, Wang C, Li Y, Li L. Heme oxygenase-1 is an equid alphaherpesvirus 8 replication restriction host protein and suppresses viral replication via the PKCβ/ERK1/ERK2 and NO/cGMP/PKG pathway. Microbiology Spectrum. 2024 Apr 2;12(4):e03220-23. https://journals.asm.org/doi/pdf/10.1128/spectrum.03220-23  

7. Wang T, Hu L, Li R, Ren H, Li S, Sun Q, Ding X, Li Y, Wang C, Li L. Hyperoside inhibits EHV-8 infection via alleviating oxidative stress and IFN production through activating JNK/Keap1/Nrf2/HO-1 signaling pathways. Journal of Virology. 2024 Apr 16;98(4):e00159-24. https://journals.asm.org/doi/pdf/10.1128/jvi.00159-24  

8. Macleay CM, Carrick J, Shearer P, Begg A, Stewart M, Heller J, Chicken C, Brookes VJ. A scoping review of the global distribution of causes and syndromes associated with mid-to late-term pregnancy loss in horses between 1960 and 2020. Veterinary Sciences. 2022 Apr 13;9(4):186. https://www.mdpi.com/2306-7381/9/4/186  

9. Adams MJ, Lefkowitz EJ, King AM, Harrach B, Harrison RL, Knowles NJ, Kropinski AM, Krupovic M, Kuhn JH, Mushegian AR, Nibert M. Changes to taxonomy and the International Code of Virus Classification and Nomenclature ratified by the International Committee on Taxonomy of Viruses (2017). Archives of virology. 2017 Aug;162(8):2505-38. https://link.springer.com/content/pdf/10.1007/s00705-017-3358-5.pdf  

10. Balasuriya UB, Carossino M. Reproductive effects of arteriviruses: equine arteritis virus and porcine reproductive and respiratory syndrome virus infections. Current opinion in virology. 2017 Dec 1;27:57-70. https://www.sciencedirect.com/science/article/am/pii/S1879625717301049  

11. Zhang Z, Guo K, Chu X, Liu M, Du C, Hu Z, Wang X. Development and evaluation of a test strip for the rapid detection of antibody against equine infectious anemia virus. Applied Microbiology and Biotechnology. 2024 Dec;108(1):85. https://link.springer.com/content/pdf/10.1007/s00253-023-12980-9.pdf  

12. Otzdorff C, Beckmann J, Goehring LS. Equine arteritis virus (EAV) outbreak in a show stallion population. Viruses. 2021 Oct 24;13(11):2142. https://www.mdpi.com/1999-4915/13/11/2142  

13. Akter R, Sansom FM, El-Hage CM, Gilkerson JR, Legione AR, Devlin JM. A 25-year retrospective study of Chlamydia psittaci in association with equine reproductive loss in Australia. Journal of medical microbiology. 2021 Feb;70(2):001284. https://www.microbiologyresearch.org/content/journal/jmm/10.1099/jmm.0.001284?crawler=true&mimetype=application/pdf