A way to improve or resolve a condition or diagnosis. This might include resolving the underlying cause or treating the signs of disease (symptomatic treatment).

Cost: $100 to $500

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.

YOUR VET MAY Recommend

Sterile Glass Marble Placed in Uterus

Cost: $100 to $500

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.


A small glass marble (usually 35mm in diameter) can be placed in a mare's uterus to suppress behavioral estrus. Other materials may be used too - stainless steel and plastic spheres have been shown to have similar effect. It is essentially an IUD (intra-uterine device).

The presence of the ball in the uterus causes the corpus luteum (the ovarian structure that produces progesterone) to remain after ovulation. This keeps the level of progesterone elevated enough to suppress estrus for a period of time.

After sterilization in an autoclave, the ball is inserted through the cervix into uterus within 24 hours after ovulation, while the mare is still in heat. Ultrasound and palpation is often used to ensure proper timing. Generally, mares tolerate the balls well. They are occasionally lost and are easily removed. Timing of placement is key.

my vet's role


The marble may be lost. If the marble is too small, it can be easily expelled.

Sometimes people forget to remove the balls. Vets occasionally find multiple IUD devices in the uterus of mares. In some cases, this can result in uterine injury. Occasionally, the glass balls may break or shatter (when they come into contact), resulting in uterine injury and development of scar tissue.

This treatment only works in a percentage of mares. In my experience, about 50% of mares have a prolonged period where they do not show heat.

If you are not the first owner of the mare or otherwise do not know her complete reproductive history, talk to your vet about examining the mare to confirm that no marbles are already in her uterus.


Not usually used in conjunction with oral hormone therapy. Not used in mares with existing uterine problems like infection.

your role

Is it working? Timeframe for effect.
Immediate. A mare should not show estrus signs once the marble has been placed. This should last a variable period of time; several months at minimum.
Questions To Ask Your Vet:
  • Should we confirm that no marbles are already in the mare?
  • What is the success rate, in your experience?
  • Should we try this treatment before we use oral progestin (Regumate)?
  • What has your experience been with the placement of a marble "IUD"?
  • When will the marble be removed?
  • What are the dangers in using this treatment?

further reading & resources

Related References:

Vanderwall, DK. Is it time to retire the use of intrauterine glass balls for estrus suppression in mares. JAVMA Vol. 247, No. 4 August 15, 2015

Author: Doug Thal DVM Dipl. ABVP