🐴 Factors Affecting Pregnancy in Performance Mares: Vet-Backed Strategies for Breeding in 2025 🧬🏇

By Dr Duncan Houston BVSc

Performance mares are athletic, driven, and often under saddle even during breeding season. But in 2025, science now confirms that the intensity and timing of exercise can negatively impact fertility. Here’s what you need to know if your goal is a healthy pregnancy and a successful foaling season. 🧠🐎

💡 Research Behind the Concern

Recent studies have evaluated how exercise—particularly in hot and humid conditions—affects mares during the breeding season. 🔬

Study Setup:

• 📍 Mares were divided into two groups
• 🐎 One group exercised at a long trot and canter for 30 minutes in heat & humidity
• 🛌 The control group was not exercised

Key Conditions:

• 🌡️ Temperatures > 86°F (30°C)
• 💧 Humidity > 50%

📉 Results: What Happened?

• 🔻 Exercised mares developed smaller follicles
• 📉 Fewer embryos were recovered from the exercised group
• ⚠️ Embryo quality was significantly lower in exercised mares

Bottom line? Exercise during heat and ovulation can reduce conception rates and embryo viability. 🚫

🧪 Cortisol’s Role in Fertility

The likely culprit behind these changes is cortisol, the stress hormone. 🧠

Researchers noted:

• 📈 Higher heart rates and cortisol levels in exercised mares
• 💓 Increased ovarian blood flow—but this didn’t improve embryo outcomes

🚚 Is Transport Stress the Same?

You might assume that transportation stress also hurts fertility—but that’s not the case.

• 🚚 Mares transported to breeding farms showed elevated cortisol
• 🔬 But no decrease in ovulation or conception rates was observed

In other words, light transport is okay—but intense physical exercise in heat is not. ✅

📋 Breeding Season Exercise Guidelines

❌ Avoid During:

• 📆 Days leading up to and including ovulation
• ☀️ Hot, humid weather conditions

✅ Safe Practices:

• 🚶 Hand walking or light turnout in the shade
• 🧊 Exercise during cooler times of day (early morning or evening)

Always prioritize reproductive monitoring via ultrasound to time breeding accurately and reduce environmental stress. 🩺

🧬 Performance vs. Pregnancy: Finding the Balance

While keeping mares fit during pregnancy is important, early gestation and breeding timing are not the best times for high-output training. 💡

If performance is the priority for the season, consider embryo transfer so your mare can stay in work while a recipient mare carries the foal. 🤱

📲 Ask A Vet for Breeding & Training Balance

Planning to breed your performance mare? Visit AskAVet.com or use the Ask A Vet App to schedule cycle tracking, exercise management, and post-breeding care. 📱🐴

Dr Duncan Houston and the team can help optimize fertility protocols, exercise schedules, and prevent early pregnancy loss due to cortisol spikes. 💬🧠

🏁 Final Thoughts

In 2025, we know that exercise can harm fertility—but timing is everything. Skip the heat workouts during ovulation, monitor cortisol-inducing stressors, and give your mare every chance at a healthy pregnancy. 🐴❤️

Need help syncing performance with breeding? Visit AskAVet.com to get started today 🐎🧬