🐴 Progesterone Supplementation in Mares: Smart Use in 2025 Pregnancy Care 💊🧬

By Dr Duncan Houston BVSc

Many breeders turn to progesterone supplementation to help maintain pregnancy in mares—but in 2025, evidence shows most mares don’t need it. Let’s break down when progesterone is truly necessary, when it’s not, and how to make informed decisions that save money and protect your breeding program. 🧠🐎

💡 What Is Progesterone?

Progesterone is a hormone that supports pregnancy by maintaining the uterine lining and preventing contractions. Without it, early embryonic loss or abortion may occur. 📉

🧬 Where Does It Come From?

• 📅 During the first 100 days of pregnancy: produced by the corpus luteum on the ovary
• 📆 After 100 days: placenta takes over progesterone production

This timeline is key when deciding whether supplementation is needed. 🔍

💉 When Is Supplementation Needed?

Progesterone is indicated when:

• 🧪 Blood tests show low progesterone levels early in pregnancy (before day 100)
• 🩺 The mare has a history of early pregnancy loss
• 🤒 The mare becomes acutely ill or stressed in later pregnancy (even though blood tests can't confirm need)

In some cases, mares that have had ovaries removed can maintain pregnancy with proper progesterone support. ✅

💸 Cost Considerations

Supplements like Regu-Mate® cost around $3 per day. That’s approximately $300 for just the first 100 days—and over $700 if used throughout gestation unnecessarily. 💲

Using it when not needed is a financial drain with no added benefit. 📉

🧪 Monitoring and Testing

Progesterone blood tests are reliable in early pregnancy but not useful after day 100 due to placental hormone differences. 🧬

Vet Recommendations:

• 🧪 Test progesterone levels at days 14–45 to determine need
• 🩺 Consider use later in pregnancy only if the mare is sick or at high risk

⚠️ Potential Downsides

• 🧬 Masking abortion: Mares will NOT come back into heat if they abort while on Regu-Mate
• 💊 False sense of security if pregnancy checks aren’t performed

This means it’s vital to recheck pregnancy status regularly while supplementing. 🩺

✔️ Proven Progesterone Products

The only formulations shown to be effective in mares are:

• 💊 Regu-Mate® (oral altrenogest)
• 💉 Injectable progesterone

Other products may be marketed for equine use but lack evidence of effectiveness. Stick with vet-approved options. ✅

📲 Ask A Vet for Progesterone Planning

Wondering if your mare needs progesterone support? Visit AskAVet.com or use the Ask A Vet App to get hormone testing, daily dosing schedules, and proper recheck timelines. 📱🐴

Dr Duncan Houston and the team can help you balance science and budget to ensure your mare’s pregnancy is supported—without unnecessary costs. 💬🧠

🏁 Final Thoughts

In 2025, we know that progesterone is essential in select cases—but not for every pregnant mare. Use it wisely, test early, monitor closely, and avoid overuse. Smart supplementation is better for your mare, your foal, and your breeding program. 🐣🐎

Need hormone testing or a pregnancy care plan? Visit AskAVet.com to get started 🐴💊