🐴 Suppressing Estrus in Mares: Glass Ball Risks & Safer Vet Options in 2025 🧬🚫

By Dr Duncan Houston BVSc

Many mares become irritable, distracted, or even unrideable when in heat. For riders and trainers, this can mean inconsistent training, poor performance, or outright danger. In 2025, several methods exist to suppress estrus—but one of the more controversial tools is the use of glass balls or marbles inserted into the uterus. While they were once thought to be a simple and cost-effective solution, new concerns are emerging. 🧠🐎

🧬 What Is the Glass Ball Method?

The technique involves inserting a sterile glass ball or marble into the mare’s uterus after ovulation. The theory is that the ball mimics pregnancy, preventing the mare from returning to estrus. 🍼

Reported outcomes:

• 📈 Historically shown to suppress heat in about 50% of mares
• 💊 Used as an alternative to daily hormones like Regumate

Originally considered safe and minimally invasive, the method gained popularity as a non-hormonal estrus control technique. 📉

⚠️ Complications of Glass Ball Use

Recent veterinary reports are raising serious concerns:

• 🦠 A case of severe uterine infection post-insertion
• 🧩 A case where two glass balls were inserted—both broke, leaving embedded glass shards in the uterus

It's unclear whether the damage occurred from using multiple marbles or from spontaneous breakage—but either way, it highlights the potential risks. 🛑

🔍 Why the Risks Matter

• 💥 Uterine trauma can lead to permanent scarring and infertility
• ⚠️ Infections can cause systemic illness or endometritis
• 🚫 There are no controlled studies confirming long-term safety

Given these findings, I no longer recommend the use of glass balls to suppress heat in mares. There are safer, more reliable options available. 💉

💊 Safer Alternatives in 2025

✅ 1. Daily Progestin Therapy (e.g., Regumate)

• 💉 Effective at suppressing ovulation and estrus behavior
• 📅 Must be given daily, which adds cost and labor
• ⚠️ Wear gloves—absorbs through human skin!

✅ 2. Long-Acting Injectable Progestins

• 🧪 Compounded formulations provide weeks to months of estrus suppression
• 📈 Ideal for performance mares during show seasons

✅ 3. Oxytocin Protocols

• 💉 Administered for 2–3 days post-ovulation
• 🧠 Tricks the body into prolonging the luteal phase
• ✅ Shown to delay heat without hormones or implants

📋 Which Option Is Right for Your Mare?

Factors to consider include:

• 🔁 Frequency and severity of estrus behaviors
• 📅 Length of suppression needed
• 💵 Budget and convenience
• 🔬 Mare's overall health and breeding status

Your veterinarian can tailor an estrus control plan that balances performance, safety, and future fertility. 🧠

📲 Ask A Vet for Hormone Planning

Want help controlling your mare’s heat cycle for competition or training season? Visit AskAVet.com or use the Ask A Vet App to explore safe options for your horse’s behavior and health. 📱🐴

Dr Duncan Houston and the team can recommend dosing protocols, time ovulation checks, and monitor for side effects. 💬🧬

🏁 Final Thoughts

While once seen as a simple solution, glass ball estrus suppression now poses too many risks to justify use. In 2025, modern hormone therapy and oxytocin protocols offer safer, proven options to help mares perform comfortably—without damaging their reproductive system. 💡🐎

Need help managing estrus in your mare? Visit AskAVet.com to build a hormone-free, vet-approved plan 🐴💉