Colic in Broodmares: Special Considerations

It's no secret that when complications arise around foaling time, they can be life-threatening for either mare or foal. A relatively common complication for broodmares is peripartum (the last month of gestation or the first few months after delivery) colic.

At the American Association of Equine Practitioners Focus on Colic Meeting, held July 24-26 in Indianapolis, Ind., Tim Mair, BVSc, DEIM, DESTS, Dipl. ECEIM, MRCVS, of the Bell Equine Veterinary Clinic in Kent, England, discussed some of the most common complications that cause colic--which is a collective term to include most ailments that cause abdominal pain in horses--in the peripartum mare.

"Colic in the broodmare presents both diagnostic and treatment challenges," Mair said. "In the pregnant mare we are faced with not only one, but potentially two patients simultaneously, and the best course of treatment for one may not necessarily be what is best for the other."

He explained that when treating a pregnant mare for colic, the veterinarian's goal is to "identify and correct whatever abnormality is present as soon as possible, and to support placental function to maintain fetal viability throughout the remaining period of gestation."

Mair presented a review of the most common types of colic found in the peripartum mare.

Arterial Rupture

There are several arteries that commonly rupture in the broodmare, causing intense abdominal pain, hematoma in the broad ligament (which supports the uterus on either side), and/or hemorrhage. These arteries include the middle uterine artery, the utero-ovarian artery, and the external ileac artery.

Mair noted that should a hematoma (which is essentially a blood blister or bag filled with blood) form in the broad ligament following a rupture of one of the first two aforementioned arteries, the broodmare will suffer hemorrhage into her abdominal cavity if the ligament ruptures.

More so, a rupture of the iliac artery almost certainly results in death, as the mare will bleed out into her abdomen. However, fatalities can occur from any of these arterial ruptures.

"Mares whose hematomas rupture or who directly bleed into their abdomen from the start demonstrate rapid signs of shock and death," Mair added. "Mares whose bleeds are initially contained within the broad ligament may still die if the blood loss has been severe enough, or if the clot is disturbed and subsequently ruptures during the recovery phase."

Most fatal bleeds, Mair noted, occur in horses more than 18 years of age, and the first occurrence of a bleed is often fatal.

Mair explained that broodmares suffering a uterine artery rupture can experience a variety of clinical signs consistent with colic signs, including:

Sweating;
Tachycardia (excessively fast heartbeat);
Tachypnea (rapid or shallow breathing);
Pale mucous membranes;
Thready pulse (a light pulse that is barely perceptible);
Cool extremities;
Depression;
General weakness;
Collapse; and
More swelling and edema in their vulva than generally observed in broodmares after foaling.

Mair explained that rectal palpation and ultrasound are the most common diagnostic tools veterinarians use to detect arterial ruptures, and abdominocentesis (the surgical puncture of the abdomen, or a belly tap) can confirm a diagnosis.

There are two treatment routes that are routinely employed for mares that suffer an arterial rupture: the "conservative" approach and the "more aggressive" approach, as Mair described them.

"Regardless of which therapeutic option is chosen, the mare must be kept as quiet as possible so as to minimize excessive increases in her arterial pressure," he cautioned.

In the conservative treatment, Mair said the mare is kept in a quiet, dark stall to minimize stress or excitement. Depending upon which situation is least stressful for the mare, her foal will either remain with or be removed from her until she heals further. He noted that transporting a mare post-rupture is not recommended.

"Tranquilizers are used judiciously as needed to help keep the mare calm and, in the case of acepromazine, to help reduce arterial pressure directly," Mair added.

Veterinarians that choose the conservative treatment route sometimes use aminocaproic acid to prevent fibrinolysis (the process that removes blood clots from circulation by the breakdown of insoluble fibrin), which would cause the mare to bleed again. Mair said analgesics are used to control the mare's pain, and that intravenous fluids or blood transfusions are sometimes employed to preserve the mare's cardiac function.

Mair explained that the more aggressive treatment approach includes all of the aforementioned therapies in addition to aggressive intravenous fluid therapy and blood transfusions to treat the shock (i.e., replace the volume of blood that has been lost from the circulation).

"This aims to support the circulation and maintain the supply of blood and oxygen to all of the tissues in the body," Mair explained. "The risk of this aggressive therapy is that it increases the blood pressure, and this could aggravate the bleeding from the ruptured vessels."

Mares with uterine artery ruptures have a guarded prognosis, Mair noted.

"For those that survive the acute episode, it is important that they must be kept quiet for several weeks as the clot resolves and the vessels slowly repair, as increases in arterial pressure during this period can cause renewed bleeding," he added.

Final resolution of the problem could take several months, he noted, and mares that survive the first uterine artery rupture generally have an increased risk of recurrence with subsequent pregnancies, so it is often recommended that these mares not be bred back.

Small Colon Rupture

A colic-causing complication associated with foaling is the rupture of the small colon.

"During the final stage of labor, movements of the fetus can cause the small colon of the mare to become trapped between the uterus and the dorsal body wall, causing the mesentery (which is the thin veil-like tissue that suspends the bowel) to tense and tear," Mair explained.

A ruptured mesentery of the small colon can also cause a rectal prolapse, he noted. Once the mesentery of the small colon ruptures or tears, the blood supply to that area of the bowel is lost, resulting in death of that part of the small colon wall; this then causes obstructions, peritonitis (inflammation of the membrane lining the abdomen), and common signs of colic.

"Affected horses usually fail to pass feces and present with large amounts of impacted feces in the distal small colon and rectum," Mair explained. These horses' outlook is poor. Some cases can survive with surgery but in other cases the affected region of the small colon cannot be reached surgically, and the mare will die.

Perineal Trauma

Damage to the vagina and anus--or perineal trauma-- that occurs during foaling can cause "significant pain" in recently foaled mares. Mair explained that affected mares often are reluctant to defecate, which leads to constipation.

"Anti-inflammatory drugs (such as phenylbutazone or flunixin meglumine) as well as local treatment with topical anti-inflammatory ointments are indicated to relived pain and swelling of tissues," Mair said, adding that walking the mare and administering oral laxatives are thought to be helpful in relieving constipation. These mares usually have a good prognosis for recovery, although they might later require surgical repair of the damaged tissues.

Colonic Displacements and Torsions

"Broodmares are especially at risk of developing large colon displacements and torsions, especially in the first 100 days post-foaling," Mair said. This is believed to be due to the increased space within the abdomen that arises following the birth of the foal; the increased space allows the large colon to move and sometimes twist.

This ailment yields different degrees of colic-related clinical signs associated with the degree of displacement or torsion in the large colon, Mair explained: "A large colon volvulus (twist) will present as a violently painful colic, often with a very high heart rate (60-100 beats per minute), whereas a simple colonic displacement (without a twist) may present with mild to moderate signs of colic with a relatively normal heart rate."

He noted prompt surgical correction of the displacement is necessary in most cases: "The prognosis for mares with large colon volvulus is poor. Surgery needs to be undertaken rapidly if the mare is going to have any chance of surviving. The outlook for mares with simple displacements of the large colon (without a twist) is much better, and most affected mares will survive following surgical correction."

Uterine Ruptures

On occasion, the mare's uterus will rupture during foaling. In these cases the mare will experience peritonitis and abdominal pain. The uterus can rupture, for example, when the fetus is being maneuvered into position or when post-foaling treatment is overly vigorous, such as with a uterine lavage (i.e., flushing). One of the biggest concerns with a ruptured uterus is internal contamination with environmental irritants.

Mair noted that veterinarians can generally combat small tears with antimicrobial medications, crystalloid and colloid fluids (both commonly used in specialized fluid therapy), peritoneal drainage, and NSAIDs. Larger tears could require surgery to effectively correct, he added.

Mares with a large amount of internal contamination are typically given a poor prognosis; however, mares with smaller tears and less internal contamination often have a better prognosis.

Uterine Horn Inversion and Uterine Prolapse

Finally, Mair discussed the inversion of uterine horns and uterine prolapse, two painful and potentially dangerous conditions that often go hand in hand.

"Pain is the result of the ovary and tip of one horn becoming inverted and entrapped within the uterine (cavity)," he explained. "The condition may progress to a complete prolapsed of the uterus through the vulvar lips if left uncorrected."

Uterine horn inversions are generally characterized by acute pain within a few hours of foaling and are not typically visible from the outside. Thus, veterinarians often diagnose a uterine horn inversion through a rectal palpation.

Several steps for treating uterine horn inversions and uterine prolapsed include:

Controlling the mare's pain and abdominal contractions, often through an epidural and sedation;
Manual correction of the inverted horn, which often requires using uterine relaxants and sometimes general anesthesia;
Replacement of the horn and ovary to their normal position;
Supportive therapy including intravenous fluids, NSAID pain relievers, antibiotic medication, and tetanus prophylaxis; and
Low-dose oxtytocin "may also aid in rapid normal involution and prevention of a recurrence," said Mair.

"Once the inverted uterine horn has been pushed back into its normal position, the outlook for the mare is generally excellent," Mair concluded.

Take-Home Message

An understanding the types of colic that often arise in broodmares can help an owners keep their mares happy and healthy before, during, and after parturition and birth. Of course, any health concerns should be addressed by a veterinarian.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.