Researcher explores innovative treatments for bacterial infections causing pregnancy loss in mares

LEXINGTON, Ky. (Oct. 28, 2026) — A University of Kentucky researcher is developing a new approach to protect pregnant mares from bacterial infections that can cause foal loss. The research could help horse breeders prevent reproductive losses while addressing growing concerns about antibiotic resistance.

Yosra Helmy, Ph.D., an associate professor of veterinary science in the UK Martin-Gatton College of Agriculture, Food and Environment (CAFE), has received funding from the American Quarter Horse Foundation to investigate whether specially developed chemical compounds, known as small molecules, can control bacteria responsible for abortions in mares.

The project, titled “Development of Novel Small-Molecule Therapeutics to Control Pathogens Causing Abortion in Mares,” will focus on finding alternatives to conventional antibiotics, which do not always successfully treat these infections.

“In many cases, losing a pregnancy represents the loss of an entire breeding season, substantial veterinary and management expenses and uncertainty about a mare’s future reproductive performance,” Helmy said. “Our research is driven by the need to develop new therapeutic approaches that could help veterinarians protect both the mare and her developing foal.”

One of the project’s primary targets is Streptococcus equi subspecies zooepidemicus, commonly called Streptococcus zooepidemicus. The bacterium can normally be found in horses without causing illness, but under certain conditions, it can enter the reproductive tract and cause serious infections. Other bacteria, including Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae, can cause similar reproductive problems.

These bacteria can cause a serious infection called ascending placentitis. The infection happens when bacteria enter the mare’s reproductive tract and spread to the placenta, which provides oxygen and nutrients to the developing foal. When the placenta becomes infected and inflamed, the foal may not receive everything it needs to grow and stay healthy. This can lead to premature birth or cause the mare to lose her foal before it is born.

“Veterinarians commonly rely on antibiotics to treat bacterial infections in pregnant mares,” Helmy said. “Although these treatments can be effective, they do not always eliminate infections, particularly when bacteria become resistant to the medications being used.”

Antibiotics can also affect microbial communities, raising additional questions about their broader effects on reproductive health. Furthermore, bacterial biofilms can complicate treatment by contributing to persistent infections and making it difficult to achieve effective drug concentrations at the site of infection.

“The goal is to find treatments that can control the infection and potentially reduce reliance on conventional antibiotics while limiting the emergence and spread of antimicrobial resistance,” Helmy said.

Searching for the next generation of treatments

The researchers aim to identify compounds that effectively target harmful bacteria while assessing their effects on host cells, their potential impact on beneficial microorganisms and their ability to reduce reliance on conventional antibiotics.

The research will evaluate the most promising candidates for activity against antibiotic-resistant bacterial strains, biofilm prevention or disruption and potential toxicity to mammalian cells. These studies are essential steps toward identifying compounds that may be suitable for future therapeutic development.

The project will draw on the expertise and resources of the Centers of Biomedical Research Excellence for Translational Chemical Biology to search for new ways to fight bacterial infections in horses. Researchers will work with Helmy’s laboratory to identify and test promising compounds, including those found in nature, that could stop harmful bacteria from growing or spreading. They will also study whether these compounds can prevent bacteria from forming biofilms. The goal is to find potential new treatments for bacterial infections that affect horses’ reproductive health.

The work is still in its early stages, and researchers must evaluate the compounds before determining whether they could become safe, effective treatments for pregnant mares. If successful, the work could eventually give veterinarians another option for managing reproductive infections, help breeders reduce foal losses and support efforts to limit antibiotic resistance.

“For the equine industry, even modest improvements in preventing infectious abortions could have meaningful benefits,” Helmy said. “Protecting a pregnancy means more than saving a potential foal; it can also help preserve a mare’s reproductive health and protect the investments breeders make in future generations of horses.”

The research reported in this article was made possible in part by a grant from the American Quarter Horse Foundation. The views expressed are those of the authors and do not necessarily reflect the views of the American Quarter Horse Foundation.

Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number P20GM130456. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.