removing uterine marbles from mares

It wasn’t so long ago when veterinarians would insert a marble into a mare’s uterus, a common practice for managing estrous cycles. The theory? The marble would act like an embryo and trick the mare’s body into thinking she was pregnant, thus eliminating estrus and “heat-cycle” related behaviors. However, their lack of effectiveness and overall negative health effects from prolonged placement—including endometritis and infertility—have prompted some veterinarians to call for the retirement of the practice, said Mariana Diel de Amorim, DVM, DVSc, Dipl. ACT, who’s on faculty at Cornell University’s College of Veterinary Medicine.

Diel de Amorim presented “How to Successfully Recover Intrauterine Marbles and Foreign Bodies Using Manual Extraction or Videohysteroscopy and Endoscopic Tools” at the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas.

In addition to unreliably mitigating estrus, marbles also can be ejected spontaneously from the uterus without the owner or manager’s knowledge. When they do remain in place, intrauterine marbles can be forgotten about (usually when a mare is sold) and/or difficult to find and remove, Diel de Amorim said.

Intrauterine marbles are usually either 25 or 35 mm in size, the larger (heavier) of which are harder to remove, especially when mares have a pendulous uterus (one that hangs down loosely). These marbles are not medically approved and, despite reported problems associated with their use, cannot be recalled from use, Diel de Amorim said.

Intact marbles aren’t the only objects veterinarians need to remove from the uterus. During breeding soundness exams, veterinarians report finding fetal bones, broken endometrial swab tips, swap caps, and glass shards from broken marbles. Diel de Amorim said veterinarians have associated the presence of these foreign bodies with:

  • Pyometra (uterine infection);
  • Adhesions (internal scarring);
  • Failure to cycle;
  • Chronic endometritis (inflammation of the uterine lining);
  • Infertility; and
  • Abortion.

In the case of marbles, Diel de Amorim said veterinarians usually find them via uterine palpation or transrectal ultrasound. While they can usually readily detect marbles in a non-pendulous uterus, that isn’t usually true in mares with pendulous uterus, in which case “transrectal ultrasound examination is imperative,” she said.

She advises mapping the foreign body’s location and estimating its size via imaging before attempting extraction.

If marble (or foreign body) retrieval is expected to take longer than 20 minutes or if hysteroscopy (using endoscopy through the cervix to inspect the uterine cavity) is necessary, Diel de Amorim recommends sedating the mare. The procedure is also easiest when a mare is in estrus because the cervix is softer and more easily dilated. The veterinarian can induce estrus with a prostaglandin if necessary. Shards or foreign bodies can create significant endometrial inflammation just 24 hours after their placement, so Diel de Amorim does not advise waiting for estrus in these cases.

Veterinarians can remove some easily accessible foreign bodies with a sterile, gloved hand or a two-handed approach, one through the rectum to manipulate the marble from outside the uterus through the cervix, and the other hand to retrieve the marble via the vagina. “This has an increased risk of rectal tear, so it might be easier to do hysteroscopy than having to do several rectal and vaginal manipulations,” Diel de Amorim said.

Other objects might be more challenging to remove, either because of their position in the uterus or because they’ve grown into the endometrium.

For more complex cases, veterinarians can use videohysteroscopy and endoscopy to remove the marble or foreign body. This is a two-person approach that requires one person to hold the scope in place through the cervix and another to operate the endoscope. Veterinarians have several endoscopic tools at their disposal for removing marbles and foreign bodies from a mare’s uterus, including snares, loops, and baskets of various sizes for grabbing and manipulation. They insufflate (fill with air) the uterus and work as a team to remove the marble or foreign body using one of these tools.

Take-Home Message

Veterinarians retrieve most foreign bodies from the mare uterus manually; however, more challenging cases, such as objects lodged in the endometrium or a mare with a pendulous uterus containing a large marble, might benefit from the use of hysteroscopy tools and equipment.

And, Diel de Amorim reminded attendees, “Marbles are nonmedically approved devices and several reports have warranted their retirement.”