Ask Your Veterinarian Presented By Kentucky Performance Products: Why Are Broodmares So Prone To Colic? - Horse Racing News | Paulick Report

Ask Your Veterinarian Presented By Kentucky Performance Products: Why Are Broodmares So Prone To Colic?

Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock.

Question: Why are broodmares so prone to colic, and what colic causes are most common for them?

Dr. Katy Dern, Rood and Riddle Equine Hospital: According to the Centers for Disease Control, 1.4 percent of human delivery hospitalizations in the United States in the year 2014 developed what are characterized as severe maternal morbidities. This means that, even in closely supervised and intensively managed births, 1.4 in every 100 women developed potentially life-threatening complications. Parturition (birth) has potential consequences for the mother, and broodmares are no exception to this biologic reality.

Dr. Kathryn Dern

When we discuss colic (abdominal pain) in the broodmare, the cause of the pain can be broadly divided into two categories: pain originating from the gastrointestinal tract and pain originating from the reproductive tract.

Colic signs attributable to the gastrointestinal tract are a common phenomenon in the broodmare, and can be further subdivided into those conditions seen prior to foaling and those seen in the post-parturient time period (after foaling). Prior to foaling, causes of colic include mild discomfort due to expanding uterine size and fetal movements, as well as displacements or abnormal motility of the large colon, cecum, or small intestine. Mares exhibiting colic secondary to fetal movements or impingement of the gravid uterus on the gastrointestinal tract will usually not have dramatic changes in their vital parameters (heart rate, respiratory rate, mucous membrane color), and will respond to analgesics (pain management). If the mare's colic signs do not respond to pain management or increase in severity, she may have a gastrointestinal issue which can be life threatening to her and/or the foal. In either case, veterinary evaluation is important to differentiate between mild and more severe forms of colic, and to ensure that more aggressive medical and surgical interventions can be instituted if necessary.

After foaling (and sometimes before foaling), gastrointestinal causes of colic can include large colon volvulus (twist) or displacement, cecal dysmotility or rupture, small intestinal incarceration, mesenteric tears leading to loss of intestinal viability, or rectal prolapse. Of these the most discussed and by far most common cause of colic is large colon volvulus. Broodmares are largely overrepresented in the large colon volvulus (LCV) caseload: one study evaluating the distribution of surgical LCV cases at a large referral hospital in California found that half of the admissions were broodmares that had foaled less than 60 days prior to admission.  This association between foaling and subsequent development of colonic displacement or LCV has been mirrored in multiple studies across various geographic areas and additional risk factors such as increased hours of stabling, increased feeding of concentrates, decreased dry matter intake, or a recent change in pasture have also been discovered.

Although our research has clearly shown that post-foaling broodmares are likely to develop large colon volvulus, we unfortunately have not yet determined exactly why they are prone to this disease. Common sense dictates that the presence of additional “room” in the abdomen post foaling must play a role, but this unfortunately does not account for the LCV cases we see in geldings, show horses, or preparturient [pregnant] mares.

Recent investigations into the role of intestinal microbiota in the development of colic suggest that significant changes in the fecal microbiota precede the development of colic. The changes in the bacterial population observed in the fecal samples of mares that developed colic are consistent with changes seen in both dysbiosis (imbalance in gastrointestinal bacteria) and inflammatory intestinal disease in other species, including humans. Further investigation into the role of intestinal microbiota in the development of large colon volvulus will hopefully allow us to not only fully characterize the disease process, but eventually identify at-risk mares and intervene prior to development of colonic displacement or volvulus.

Other gastrointestinal causes of post-foaling colic are usually more directly linked to the parturition itself. Cecal bruising or rupture can occur when the foal traumatizes the base of the cecum. These mares commonly present with abdominal discomfort within the first few days of foaling and then progress to signs of septic peritonitis (abdominal infection) if the wall of the cecum becomes devitalized to the point of rupture. Tears in the mesentery of the small colon or small intestine can subsequently trap segments of the small intestine, causing pain from the entrapment itself and, if prompt surgical intervention is not undertaken, these small intestinal segments can become devitalized, endangering the mare's life, necessitating resection (removal of the devitalized area). If the small colon mesentery is affected, the tear itself can often affect the blood supply to the small colon, causing a gradual necrosis (death) of a segment of the small colon requiring surgery.

Reproductive causes of colic are also common in the broodmare, and determining whether colic signs are gastrointestinal or reproductive in nature is one of the primary goals of the colic exam. In the pregnant mare, colic signs attributable to the reproductive tract can range from mild, medically manageable colics due to fetal shifting and increased fetal size, or abdominal discomfort can be a sign of more life threatening conditions such as uterine torsion or preparturient uterine artery hemorrhage. As with all signs of colic, evaluation by your veterinarian is indicated if your mare's colic signs do not resolve or increase in severity.  On the farm, your veterinarian may perform a physical, rectal, and/or ultrasonographic exam to determine if referral is indicated.

In the post foaling broodmare, causes of colic signs attributable to the reproductive tract include mild colic signs due to normal uterine contraction and involution, or more severe colic signs secondary to uterine artery rupture, uterine tears, invagination of a uterine horn or uterine prolapse. In the case of uterine artery rupture, the mare will often show signs of abdominal pain if the hemorrhage is limited to the broad ligament (soft tissue structure which suspends the uterus within the abdomen), as the hematoma dissects through the ligament itself. If she is bleeding freely into her abdomen however, she may not show signs of colic, rather exhibiting a high heart rate, anxiety, and increased respiratory rate consistent with blood loss. In these cases, a thorough physical exam, rectal palpation, abdominal ultrasonography, and abdominocentesis (analysis of a sample of the abdominal fluid) can be critical in determining whether or not the mare is actively hemorrhaging.

Uterine tears can present a diagnostic challenge, as they occur during foaling but do not necessarily cause signs of abdominal pain until the leakage of uterine fluid into abdomen causes signs of abdominal infection (septic peritonitis). In these cases, the mare often presents within the first few days after foaling for dullness and depression, fever, and high heart rate. The diagnosis of septic peritonitis is made using abdominal ultrasonography and abdominocentesis. Prompt surgical repair of these tears, often found at the tip of the uterine horn, limits the continued contamination of the abdomen and allows for intraoperative lavage of the abdomen with drain placement for post-operative lavages. Cases of invagination of the uterine horn are often diagnosed and treated on farm, but if they progress to uterine prolapse may necessitate referral for replacement under general anesthesia.

Lacerating or tearing the cervix during foaling is usually not painful and is commonly found later when the mare is spec'ed or when she is cultured. Manual examination of the cervix is required to definitively diagnose a cervical tear, which are usually repaired after the initial swelling from foaling has subsided (approximately three weeks after parturition).

It is important to note that just because a mare had an uneventful foaling does not mean that the foal didn't damage segments of the reproductive or gastrointestinal tract during parturition. In all cases of broodmare colic, evaluation by a veterinarian experienced in broodmare disorders and timely referral, if necessary, are critical to survival of both mare and foal.

Dr. Katy Dern is originally from Colorado and Montana. She attended Washington State University for her undergraduate work, and Colorado State University for her veterinary degree. Following graduation from CSU in 2012, she completed an internship at Peterson and Smith Equine Hospital in Ocala, followed by an internship at Rood and Riddle Equine Hospital. After her internships, Dr. Dern completed a three-year surgical residency at The Ohio State University, while also earning a Master's of Science Degree. She became board certified in equine surgery in 2018 and has been the surgeon at Rood and Riddle's Saratoga hospital since 2017. 

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