🐴 Breeding-Induced Endometritis in Horses: Preventing Infertility in 2025 🧬💉

By Dr Duncan Houston BVSc

Infertility in broodmares is one of the most frustrating challenges in equine reproduction. One often-overlooked cause is breeding-induced endometritis (BIE)—a condition that doesn’t always involve infection, but still prevents pregnancy. In 2025, improved diagnostics and targeted uterine therapy are helping more mares carry healthy foals to term. 🧠🐎

💡 What Is Breeding-Induced Endometritis?

Endometritis is inflammation of the uterine lining, and while infection is a common cause, inflammation can also be triggered by breeding itself. This is referred to as breeding-induced endometritis (BIE). 🧪

Normally, after mating or insemination, the mare’s uterus mounts a short-term inflammatory response to:

• 🧼 Remove bacteria introduced during breeding
• 💧 Clear excess semen and seminal fluid

In healthy mares, this response resolves within 48 hours. But in susceptible mares—especially older mares—this inflammation persists, creating an environment hostile to embryo implantation. 🚫

📅 When the Problem Starts

The embryo drops from the oviduct into the uterus around days 5–6 post-ovulation. If inflammation is still present at that time, the uterus is not receptive to implantation, and the pregnancy fails silently. ⚠️

🧠 Why Older Mares Are at Higher Risk

As mares age, the uterine immune system becomes less efficient. These mares often:

• 📉 Have slower uterine clearance of fluid
• 🧬 Mount prolonged inflammatory responses
• 📍 Show no signs of infection but fail to conceive

This makes older maiden mares particularly prone to persistent BIE. 🐴

🔬 Diagnosing Breeding-Induced Endometritis

Key diagnostic indicators include:

• 📸 Ultrasound: Shows fluid accumulation in the uterus post-breeding
• 🔬 Cytology: Detects inflammation but no infection
• 🧪 Culture: Negative for bacteria in many cases

If inflammation is still present 18–48 hours after breeding, persistent BIE is likely. 📋

💉 Treatment Options in 2025

✅ Uterine Lavage

• 🧼 Flushes out semen, bacteria, and debris
• 💧 Typically performed with sterile saline or lactated Ringer’s

✅ Oxytocin Injections

• 💉 Administered to stimulate uterine contractions
• 📆 Often given every 4–6 hours after breeding

✅ Corticosteroids

• 🧠 Used to suppress excessive inflammation in select cases
• ⚠️ Only used under close veterinary supervision

✅ Immunomodulators

• 🧬 Drugs that support a more balanced uterine immune response
• 🔁 Often used alongside lavage and oxytocin

⚠️ When NOT to Use Antibiotics

Because BIE is usually non-infectious, antibiotics are not recommended unless a confirmed infection is present. Overuse can disrupt the uterine environment and delay healing. 🛑

📋 Managing Mares with BIE

• 📆 Track fluid on ultrasound before and after each breeding
• 🧬 Use semen of high quality to reduce inflammation
• 📉 Breed only once per cycle to reduce uterine load
• 🧠 Consider embryo transfer if inflammation persists despite treatment

📲 Ask A Vet for Breeding Consults

If your mare has failed to conceive without obvious infection, visit AskAVet.com or use the Ask A Vet App for an inflammation-focused fertility plan. 📱🐴

Dr Duncan Houston and the team can help evaluate cytology, fluid scores, and treatment response to identify and manage breeding-induced endometritis. 🧬💬

🏁 Final Thoughts

In 2025, persistent endometritis isn’t just about infection. For older or hard-breeding mares, it’s often a question of timing, inflammation, and uterine tone. With the right diagnostics and gentle, non-antibiotic therapies, pregnancy is still very possible. ❤️🐎

Struggling with repeat breedings? Visit AskAVet.com to help your mare conceive with confidence 🧬🐴