NAVLE Reproductive

Equine Uterine Artery Rupture Study Guide

📅 March 28, 2026 ⏱ 25 min read

Overview and Clinical Importance

Uterine artery rupture (periparturient hemorrhage) is a life-threatening emergency that occurs when arteries supplying blood to the equine reproductive tract rupture, typically around the time of foaling. This condition represents one of the most common causes of death in periparturient mares, accounting for up to 40% of postpartum mare fatalities. Understanding the pathophysiology, clinical presentation, and emergency management of this condition is essential for NAVLE success and clinical practice.

The condition predominantly affects older, multiparous mares (greater than or equal to 15 years of age) and can occur before, during, or after parturition. In a 15-year necropsy study of 513 horses with periparturient arterial rupture, 78% were 15 years of age or older. The hemorrhage may be contained within the broad ligament (forming a hematoma) or rupture into the abdominal cavity (hemoabdomen), with the latter carrying a significantly worse prognosis.

Artery	Origin and Course	Clinical Significance
Uterine Artery (Middle Uterine Artery)	Branch of the EXTERNAL iliac artery (unique to mares); courses through the mesometrium (broad ligament) toward the uterine horn	MOST COMMONLY RUPTURED vessel; rupture typically occurs within 15 cm of the bifurcation from the external iliac
Uterine Branch of Ovarian Artery	Cranial uterine artery; anastomoses with uterine artery at cranial aspect of uterine horn	Less commonly affected; supplies cranial portion of uterine horns
Uterine Branch of Vaginal Artery	Caudal uterine artery; anastomoses with uterine artery at caudal aspect; supplies cervix and caudal uterus	Rarely affected; provides collateral supply

Vascular Anatomy of the Equine Uterus

Understanding the blood supply to the mare's uterus is critical for comprehending the pathophysiology of uterine artery rupture. The arterial supply to the equine uterus is unique compared to other domestic species and involves three main vessels:

Arterial Blood Supply to the Equine Uterus

High-YieldSPECIES DIFFERENCE - In mares, the main uterine artery arises from the EXTERNAL iliac artery. This is unique compared to cows and dogs where the main uterine blood supply comes from branches of the internal iliac (vaginal or umbilical arteries). This anatomical distinction is a favorite NAVLE question!

The Broad Ligament (Mesometrium)

The broad ligament is a double layer of peritoneum that suspends the uterus from the dorsal body wall. It consists of three parts: the mesovarium (attaches to ovary), mesosalpinx (attaches to uterine tube), and mesometrium (attaches to uterus). The uterine artery courses through the mesometrium, and when rupture occurs, blood can be contained between the two serosal layers, forming a hematoma. If the pressure becomes too great, the broad ligament ruptures, leading to free hemorrhage into the peritoneal cavity (hemoabdomen).

Risk Factor	Clinical Significance
Advanced Age (greater than or equal to 15 years)	78% of cases occur in mares 15 years or older; probability increases with each pregnancy beyond 10 years
Multiparity	Repeated vessel stretching during pregnancies causes cumulative vascular damage; incidence of angiosis: 18% in mares less than or equal to 5 years, 82% in mares greater than 20 years
Dystocia	Increased intra-abdominal pressure and prolonged straining increase risk of arterial rupture
Previous History	Mares that survive uterine artery rupture have higher recurrence risk in subsequent pregnancies
Timing	Most common during/after parturition: 29.6% prepartum, 59.1% during parturition, 11.3% postpartum

Pathophysiology and Risk Factors

Arterial Wall Degeneration

Research has identified specific degenerative changes in the arterial walls of affected mares. A landmark study by Ueno et al. (2010) examining 31 Thoroughbred mares with fatal peripartum hemorrhage found consistent pathological changes:

Smooth muscle atrophy of the tunica media
Fibrosis of the tunica media
Calcification of the internal elastic lamina
Aneurysm formation at vessel bifurcations

These degenerative changes are believed to result from repetitive cyclic loading of the arterial walls associated with maintaining pregnancy, combined with increased wall shear stress at points of bifurcation or curved areas of the arteries. The hemodynamic changes during parturition (increased blood pressure, intra-abdominal pressure, and heart rate) serve as the final trigger for rupture.

Risk Factors

NAVLE TipRemember "OLD MAMAS BLEED" - O = Old age (greater than 15 years), L = Long breeding history, D = Dystocia risk, M = Multiparity, A = Arterial degeneration, M = Mesometrium rupture, A = After foaling (most common), S = Shock signs, B = Broad ligament hematoma, L = Lactate monitoring, E = Emergency treatment, E = Early detection saves lives, D = Don't stress the mare!

Parameter	Broad Ligament Hematoma	Hemoabdomen
Primary Signs	Colic signs predominate (pawing, rolling, flank watching)	Hemorrhagic shock signs predominate (may have less pain)
Heart Rate	Elevated (60-80+ bpm)	Markedly elevated (greater than 80 bpm), weak pulse
Mucous Membranes	Pale pink, may be tacky	Very pale to white, prolonged CRT
Temperature	Normal to low	Low (hypothermia in severe shock)
Rectal Palpation	Fluctuant mass in broad ligament	Edematous broad ligament; may feel normal
Other Signs	Sweating, anxiety, lip curling	Sweating, trembling, ataxia, pupillary dilation, collapse
Prognosis	Fair to good if contained; usually stabilizes within 24 hours	Guarded to poor; rapid deterioration possible

Clinical Presentation

Clinical presentation varies depending on whether hemorrhage is contained within the broad ligament or ruptures into the abdominal cavity. Experienced owners often recognize the classic presentation: a pawing, sweating postpartum mare with a lifted lip (flehmen response to pain).

Comparison of Clinical Presentations

High-YieldCRITICAL DISTINCTION - Mares with hemorrhage contained in the broad ligament typically show MORE PAIN (colic signs) because the expanding hematoma stretches the peritoneal layers. Mares with hemoabdomen may show LESS PAIN but have more severe signs of shock. A mare that transitions from colic to shock signs suggests broad ligament rupture with progression to hemoabdomen!

Diagnostic Test	Expected Findings	Clinical Significance
PCV/TS	May be normal initially; PCV drops before TS in acute hemorrhage; PCV less than 15% indicates severe blood loss	Serial monitoring essential; initial values may not reflect severity
Blood Lactate	Normal less than 2.0 mmol/L; elevated values indicate tissue hypoperfusion	Rising lactate despite fluid therapy = indication for blood transfusion
Transabdominal Ultrasound	Swirling heterogeneous/hyperechoic free fluid in abdomen (hemoabdomen); hypoechoic/hyperechoic mass in broad ligament (hematoma)	QUICKEST method to confirm hemoabdomen; also useful for monitoring hematoma size
Transrectal Ultrasound	Hyperechoic mass adjacent to uterine horn within broad ligament	Useful for characterizing hematoma; use caution - rectal exam may increase BP
Abdominocentesis	Grossly bloody fluid that does not clot (distinguishes from iatrogenic splenic puncture)	Confirms hemoabdomen; PCV of peritoneal fluid should approach blood PCV

Diagnosis

Diagnosis is based on a combination of clinical signs, history, physical examination, ultrasonography, and abdominocentesis. CRITICAL: Handle suspected cases with extreme care - stress can destabilize clots and increase hemorrhage!

Diagnostic Approach

Physical Examination Considerations

Minimize stress - keep foal visible to mare, use chemical restraint if needed
Avoid nose twitch - can induce collapse
Rectal examination may be abbreviated or avoided - abdominal press can disrupt thrombus
Obtain HR, RR, temperature, and mucous membrane assessment first

Diagnostic Tests and Findings

Differential Diagnosis

Clinical signs of postpartum hemorrhage can mimic other periparturient emergencies:

Uterine rupture - may cause hemorrhage and peritonitis
Large colon volvulus/displacement - severe colic, may have concurrent GI sounds changes
Cecal rupture - septic peritonitis develops
Small intestinal strangulation - reflux, rapid deterioration
Ruptured ovarian neoplasm (granulosa cell tumor) - hemoabdomen in non-periparturient mare
Splenic rupture - trauma history, may have palpable mass

Drug Class	Drug/Agent	Dose	Notes
Antifibrinolytic	Epsilon-aminocaproic acid (EACA)	40 mg/kg IV loading in 1L saline over 30-60 min; then 20 mg/kg IV q6h	Lysine analog; inhibits fibrinolysis by blocking plasminogen activation
Antifibrinolytic	Tranexamic acid	5-25 mg/kg IV slow bolus q12h	8-10x more potent than EACA; may be preferred
Herbal Hemostatic	Yunnan Baiyao	8-13 mg/kg PO q12h	Anecdotal use; studies show no effect on hemostatic parameters in horses
Sedation/Analgesia	Xylazine	0.25-0.5 mg/kg IV as needed	Provides sedation and analgesia; use low doses to avoid hypotension
Sedation/Analgesia	Butorphanol	0.01-0.02 mg/kg IV	Opioid analgesia with minimal cardiovascular effects
NSAID	Flunixin meglumine	1.1 mg/kg IV q12-24h	Anti-inflammatory and analgesic; may affect platelet function
Ecbolic	Oxytocin	2-10 IU IM q4-6h	Promotes uterine involution; use LOW doses - controversial in active bleeding

Treatment

Treatment focuses on supportive care, minimizing stress, promoting hemostasis, and managing shock. Surgery is generally NOT recommended due to anesthetic risk and difficulty locating/ligating the affected vessel.

Treatment Goals

Minimize stress - keep mare calm, foal visible, avoid unnecessary procedures
Permissive hypotension - provide perfusion support WITHOUT normalizing blood pressure
Promote coagulation/prevent clot lysis - antifibrinolytic therapy
Provide analgesia - control pain without excessive sedation
Support oxygen-carrying capacity - blood transfusion when indicated

Pharmacological Treatment Options

Fluid Therapy and Blood Transfusion

PERMISSIVE HYPOTENSION is the key concept in fluid therapy for uncontrolled hemorrhage. The goal is to provide sufficient perfusion pressure to maintain vital organ function while keeping blood pressure below normal to avoid disrupting clot formation at the rupture site.

Fluid Options

Hypertonic saline (7.2%) - rapid volume expansion; 2-4 mL/kg IV
Polyionic crystalloids (LRS) - volume replacement; titrate to clinical effect
Plasma - provides coagulation factors and proteins
AVOID hetastarch - can impair coagulation and cause renal tubular injury in volume-contracted patients

Indications for Blood Transfusion

PCV less than 15%
Lack of clinical response to crystalloid resuscitation
Persistent or rising lactate despite fluid therapy
Estimated blood loss greater than 25% of blood volume (greater than 20 mL/kg)

Transfusion Volume: Approximately 40% of estimated blood loss. Pre-crossmatching potential blood donors is recommended for high-risk mares foaling at referral hospitals.

NAVLE TipPERMISSIVE HYPOTENSION is a NAVLE favorite! Remember: DO NOT aggressively fluid resuscitate to normalize blood pressure in uncontrolled hemorrhage. Maintain just enough perfusion for vital organs while allowing clot formation. Indicators for transfusion: PCV less than 15%, rising lactate, or loss of greater than 25% blood volume. Survival rate reaches 84% when mares are diagnosed early and treated at referral hospitals!

Scenario	Prognosis and Outcome
Hemorrhage contained in broad ligament	FAIR to GOOD; mare usually stabilizes within 24 hours; hematoma organizes and resolves over 5-6 months
Hemoabdomen with early treatment	GUARDED; 50% survival rate reported; 84% survival when diagnosed early near referral hospital
Hemoabdomen with delayed treatment	POOR; rapid deterioration; high mortality
Poor prognostic indicators	High respiratory rate, persistent tachycardia, rising lactate, rapid PCV decline, progression from colic to shock

Prognosis and Long-Term Management

Future Breeding Recommendations

Do NOT breed in the same year as uterine artery rupture - hematoma disruption risk
Future foaling should occur at an equine hospital with blood transfusion capabilities
Consider elective cesarean section option for high-risk mares
Pre-crossmatch blood donors before expected foaling date
Recurrence is more likely once a mare has experienced uterine artery rupture
Some owners may elect to retire affected mares from breeding

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