Late-gestation abdominal pain in mares can be a perplexing enigma, a blend of mystery and urgency

A horse of any sex or reproductive status could experience abdominal pain from gastrointestinal (GI) distress or muscle pain in the abdomen. But a pregnant mare showing abdominal discomfort could be aborting her fetus or developing pregnancy complications.

Most colics resolve uneventfully: no surgery or even fluids needed. “Abdominal pain is common in horses in general,” notes Ashley VanderBroek, DVM, Dipl. ACVS-LA, assistant professor of large animal surgery at Michigan State University (MSU) College of Veterinary Medicine, in East Lansing.

When it comes to dealing with pregnant mares, “I would say the majority of colic cases are similar to horses that are not pregnant—usually mild and resolve on their own,” VanderBroek says. However, when a pregnant mare’s colic becomes severe, it might require “prompt surgical management.”

Causes of Late-Gestation Colic

“Colic is just a term to describe abdominal pain in the horse,” VanderBroek explains. “Most of the time that’s associated with the GI tract, but it doesn’t have to be.”

“We have to think about the GI tract, urinary tract, and reproductive tract when a horse is displaying signs of colic,” adds Julie Strachota, DVM, MS, Dipl. ACT, assistant professor and director of clinical education at MSU’s College of Veterinary Medicine.

In late gestation space is scarce in the abdomen. So, in a pregnant mare experiencing abdominal pain, “some of it could just be discomfort from everything being a little bit more compressed,” VanderBroek says.

When the mare’s internal organs get compressed and displaced, diagnostics become challenging.

“It is very, very hard to call some of these ‘GI problems’ just based on palpation or based on ultrasonography,” says Ahmed Tibary, DMV, MS, DSc, PhD, Dipl. ACT, professor emeritus in the Department of Veterinary Clinical Sciences at Washington State University College of Veterinary Medicine, in Pullman.

With abdominal distress veterinarians often discern first whether surgery will be necessary. The precise diagnosis comes later.

Gastrointestinal Colic

Notable GI colic types in pregnant mares include a large colon volvulus (rotation of the bowel), cramping from gas, and impactions in or displacements of the large colon.

A large colon volvulus occurs when the colon rotates and tightly twists around on itself, VanderBroek explains. It is more commonly seen immediately post partum. “That is the most fatal form of colic, and broodmares, particularly, are predisposed to that.

“They are violently painful, like intractable pain,” she says. Getting close enough to administer sedatives safely can be difficult.

Sometimes the colic is just gas.

“Gas is produced during digestion, so the colon needs to be able to expand,” VanderBroek says. But when there’s a “big gravid uterus,” a little gas can lead to discomfort more quickly.

“Of the GI causes (of colic in late-gestation broodmares) approximately half are medical,” meaning they can be treated without surgery, says Julie Dechant, DVM, MS, Dipl. ACVS and ACVECC, professor of clinical equine surgical emergency and critical care at the University of California, Davis, School of Veterinary Medicine. “Of those needing surgery, almost 80% are strangulating lesions.” Those are mostly found in the large intestine.

Pregnancy-Related Colic

Notable pregnancy-related colic includes uterine torsion, abortions or dystocias (difficult births), hydrops (fetal fluid accumulation in the uterus), tearing of the abdominal wall, and uterine artery bleeding.

“Uterine torsion and uterine artery bleeding each account for approximately 5% of late-gestation colic,” Dechant says.

Uterine Torsion occurs when the mare’s uterus twists on its axis, potentially cutting off blood supply and damaging the placenta. It occurs more frequently during the final three months of gestation, Strachota says.

 Veterinarians diagnose uterine torsion using transrectal palpation, which they use to check the severity and direction of the twist, Tibary says.

Mares with uterine torsions usually display mild to moderate abdominal discomfort, Strachota says. They might lie down more, have a decreased appetite, or defecate less than they should.

Cases of late-gestation mares showing signs of colic can present another issue: premature foals. These foals face such long odds that VanderBroek says she avoids delivering them early.

“If I take a mare to surgery for a uterine torsion, even if her due date is next week, I will correct the torsion, and I will leave the foal in the uterus,” VanderBroek says.

Abortion and parturition (giving birth) have similar clinical signs and can include vulvar discharge, relaxation of the prepubic tendon, and mammary development. Nesting in the stall, eating less, or isolating from other horses are other signs, Strachota says.

Dystocias can occur with live foals but are more likely if a fetus dies in the uterus.

“Horses have to be born a specific way,” with head and legs extended, VanderBroek explains. If the head or legs are bent instead of in a “forward dive” position, the mare might have difficulty delivering.

Hydrops is rare but “one of the most critical as far as emergencies,” Tibary says. Hydrops occurs when an abnormally large amount of fetal fluid accumulates in the mare’s uterus.

“The last case I had was 230 liters of fluid,” Tibary says. “That’s 230 liters pressing on the diaphragm.”

Respiratory distress can be a sign of hy- drops, he says, or they are a downer mare—one that is lying down and unable to rise.

Muscle Tone and Age can contribute to colic risk, with aging mares or those with pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease) particularly vulnerable.

“PPID generally compromises the abdominal muscle tone and, as they get heavier toward the end of pregnancy, they may have ruptured muscles or prepubic tendon rupture,” Tibary says.

Monitoring the Mare for Colic

Typical signs of colic include pawing, flank-watching, and rolling. But late-gestation mares can show broader signs, Dechant says. Watch for “changes in attitude (agitated or dull), changes in manure consistency (loose or dry), decreased or absent manure output, reduced or absent appetite, and lying down more often.”

Watch the udder “for premature signs of udder development or dripping of secretions. Vulvar discharge or development of abdominal edema or swelling are also important to monitor,” she adds.

Dechant further recommends owners learn to take their horse’s vital signs (temperature, heart rate, and respiratory rate). Late gestation mares often have mildly increased heart rates and respiratory rates. Sudden or moderate-to-severe increases in heart rate or respiratory rate are not normal, she says.

Call the veterinarian when you see obvious signs of discomfort; mild signs of discomfort that last more than one to two hours; or multiple simultaneous signs (such as mild discomfort in addition to not eating or abnormal vital signs).

Treatment Options for Late-Gestation Colic

The mare’s treatment depends on the diagnosis, of course. For late-gestation colics that get sent to the clinic, approximately half respond to medical treatment, while half require colic surgery, Dechant says.

“Some problems, such as uterine torsion, have different treatment options depending on the clinical signs, gestation length, and clinician preference,” Dechant notes. “Some problems, such as hydrops or body-wall tears, require confinement, analgesia, and abdominal support wraps.”

For other problems causing abdominal pain, the mare might need medication to fight infection or prevent pregnancy loss, Dechant says.

GI Colic Treatment

Mares with a large colon volvulus need to go straight to surgery; time is critical.

“The sooner they can get to a hospital, the sooner they can get anesthetized, the sooner that they can get on the table, the more likely they are to survive,” VanderBroek says. If it takes three or four hours to arrive at the hospital, “the likelihood that they’re going to survive decreases.”

For other kinds of GI colics, treatment might include administering non-steroidal anti-inflammatory drugs (NSAID) for pain; using a nasogastric tube to check for reflux; or administering fluids, Strachota says.

VanderBroek notes that pain plays a role in determining whether a case needs to go to surgery. Compromised blood supply is another factor. If something’s twisted or strangulating, “I recommend surgery because that’s going to be the only fix,” she says. “You cannot resolve a large colon volvulus or another strangulating lesion medically. There’s just no way to do that.”

Pregnancy-Related Colic Treatment

If your mare has uterine torsion, a veterinary team might attempt to roll the mare using the “plank on the flank” technique.

The veterinarian using this method first determines the direction of the twist—counterclockwise or clockwise. Next, after anesthetizing the mare, placing her on her side, and setting a wood plank on her belly in a specific area (TheHorse.com/124561), someone kneels on the plank, while other handlers roll the mare to her other side. The person kneeling holds the uterus still while the mare is rolled to correct the torsion.

The technique proves successful about 80% of the time, Tibary says. To attempt it veterinarians must know both how to perform the maneuver and the direction of the torsion.

“If you start rolling the mare every which way, and you don’t know the direction of the torsion, you could rupture the uterus,” Tibary says.

Veterinarians can also address torsions surgically.

“Mare survival is approximately 85-90% and up to 80% live birth rates if the mare is less than 320 days gestation, and the mare is not in shock or compromised,” Dechant says.

Prognosis After Treatment

Survival rates after colic surgery in late-gestation mares average 60-65%, slightly lower than rates in nonpregnant horses, Dechant says.

When the mare survives, “approximately 75% of these cases can have successful pregnancy outcomes” depending on the severity, she adds.

Mares with hydrops have an excellent survival rate, provided they do not have body wall tears or go into shock, Dechant says, though they typically lose the fetus. But in many of these cases, mares can be successfully rebred and deliver foals naturally.

Preventing Late-Gestation Colic

Preventing GI Colics

“Owners will say, ‘What can I do to ensure that my horse never colics?’ and my response is, ‘Don’t get a horse,’ ” VanderBroek says. “Because there’s no way to completely prevent colic.”

Still, our experts have some advice:

• Ensure horses have hay in front of them all the time so they eat throughout the day. “If the colon is full of fiber when it twists, it doesn’t compromise the blood supply quite as much,” VanderBroek says. “Horses were not meant to eat large grain meals twice daily.”
• Feed pregnant mares and lactating mares according to their body condition and their actual energy demands, says Strachota. This will ensure they receive balanced nutrition, which supports their gut health and reduces the risk of digestive disturbances.
• If you make changes in feed and management, do it gradually to help the sensitive bugs in the gut adjust.
• Hydration can prevent impactions. Try flavored electrolytes if your mare needs more water, Strachota says.

Preventing Pregnancy-Related Colics

Some pregnancy-related colics have unknown causes.

Uterine torsion is “bad luck,” VanderBroek says; there’s nothing you can do to prevent it.

Theories exist about the cause of hydrops but “we don’t really know,” Tibary says.

Strachota emphasizes the role of biosecurity in preventing abortion. Mares should be isolated from animals that have left the property and returned, and they should be kept away from high-traffic areas.

Tibary stresses the importance of checking a mare’s pregnancy early because twin pregnancies are “something that is either going to result in abortion or result in some pretty serious problems.”

If your veterinarian finds one embryo but the ovaries show more than one ovulation during the first pregnancy check, you might need to check again later, he says. Vets should examine the mare at five months of gestation to verify everything is normal. These checks can identify problems that could lead to abortion, such as a thickening or separation of the placenta.

Take-Home Message

Late in pregnancy, mares’ abdominal space is a limiting factor, and they can experience colic, whether due to gastrointestinal problems, uterine torsion, abortion, or dystocia.

“There are other possible causes for colic, but those three come to my mind first,” VanderBroek says. Deciphering a mare’s clinical signs can be tricky and time matters, so call the veterinarian sooner rather than later.