Haemoperitoneum in the Pregnant Mare: Early Recognition and Diagnostic Challenges

Haemoperitoneum (HP), or accumulation of blood within the abdominal cavity, is an uncommon but potentially life-threatening condition in horses. Clinical presentation can vary widely, ranging from mild intermittent colic to acute hypovolaemic shock and death. One of the greatest clinical challenges for equine practitioners is that early-stage haemoperitoneum may initially appear deceptively mild^1,2. 

This case involving a pregnant mare with bilateral granulosa cell tumours (GCTs) demonstrates how progressive intra-abdominal haemorrhage can evolve from subtle clinical signs into a critical emergency requiring surgical intervention^3,4. 

Case Presentation 

An 8-year-old 450 kg Warmblood-cross dressage pony mare was referred for investigation of low-grade colic signs of 24 hours duration. The mare was approximately 60 days pregnant following artificial insemination and had no previous history of reproductive abnormalities, behavioural changes, or systemic illness¹. 

On admission, the mare appeared bright and alert. 

Initial Clinical Parameters 

• Heart rate: 40 beats/min 

• Respiratory rate: 12 breaths/min 

• Rectal temperature: 37.6°C 

• Pink moist mucous membranes 

• Capillary refill time: 2 seconds 

• Normal abdominal borborygmi 

Initial laboratory findings were within normal limits: 

• Packed cell volume (PCV): 39% 

• Total protein (TP): 62 g/L 

• Blood lactate: 0.46 mmol/L 

Abdominocentesis yielded clear yellow peritoneal fluid with normal protein and lactate values. 

Diagnostic Investigation 

Transabdominal ultrasonography did not reveal any gastrointestinal abnormalities or evidence of free abdominal fluid. However, rectal palpation identified enlargement of the left ovary associated with a marked pain response. 

Transrectal ultrasonography demonstrated a well-circumscribed, encapsulated reticulated structure measuring approximately 7 cm in diameter within the left ovary¹. 

At this stage, differential diagnoses included¹: 

• Ovarian haematoma 

• Haemorrhagic follicle 

• Early ovarian neoplasia 

• Pregnancy-associated ovarian enlargement 

Because the mare was pregnant, granulosa cell tumour was initially considered less likely despite ultrasonographic findings potentially being compatible with ovarian neoplasia (Crabtree et al., 2013; Gee et al., 2012). 

Why Early Haemoperitoneum Can Be Difficult to Diagnose 

Haemoperitoneum in horses often develops progressively. Early blood loss may not immediately affect cardiovascular parameters or laboratory values because splenic contraction can temporarily maintain circulating red cell mass. 

Furthermore, pregnant mares between 60–80 days gestation commonly exhibit hormonally driven ovarian changes associated with equine chorionic gonadotropin (eCG) activity². This can make differentiation between physiological and pathological ovarian enlargement challenging. 

The mare remained clinically stable during initial hospitalisation. However, serial monitoring proved essential because progressive haemoperitoneum may initially develop with minimal cardiovascular compromise¹. 

Disease Progression 

Over the following 72 hours¹: 

• Colic signs intermittently recurred 

• The ovarian structure enlarged to approximately 9 cm 

• Transabdominal ultrasound identified swirling echogenic abdominal fluid 

• Repeat abdominocentesis yielded haemorrhagic fluid 

Peritoneal fluid analysis showed¹: 

• PCV: 28% 

• TP: 68 g/L 

• Lactate: 2.4 mmol/L 

These findings confirmed haemoperitoneum. 

The mare subsequently became intermittently tachycardic with heart rates reaching 60 beats/min. 

Clinical Red Flags for Practitioners 

This case highlights several important warning signs that should prompt concern for active intra-abdominal haemorrhage¹: 

Persistent Ovarian Pain 

Pain elicited during ovarian palpation is abnormal and should not be dismissed as routine pregnancy-associated discomfort. 

Progressive Ovarian Enlargement 

Rapid enlargement of ovarian structures over serial examinations strongly suggests active pathology. 

Development of Free Abdominal Fluid 

The appearance of echogenic swirling fluid on ultrasound is highly suspicious for haemorrhage. 

Falling Total Protein 

Total protein often decreases earlier than PCV during acute haemorrhage due to plasma loss. 

Progressive Tachycardia 

Persistent tachycardia despite analgesia should raise concern for ongoing blood loss. 

Differential Diagnoses for Equine Haemoperitoneum 

Common causes include: 

• Uterine artery rupture 

• Splenic rupture 

• Trauma 

• Mesenteric tears 

• Post-surgical bleeding 

Less common causes include: 

• Ovarian haematoma 

• Ruptured granulosa cell tumour 

• Coagulopathy 

• Neoplasia-associated bleeding 

Neoplasia has been reported to account for approximately 13% of lesions associated with haemoperitoneum in horses¹. 

Initial Conservative Management 

Because the mare initially remained haemodynamically stable, conservative management was pursued. 

Treatment included: 

• Phenylbutazone 

• Altrenogest 

• Serial ultrasonographic monitoring 

• Repeated cardiovascular assessment 

Conservative management may be appropriate in stable haemoperitoneum cases where bleeding appears self-limiting and cardiovascular compromise is absent^1,2. 

However, serial examinations are critical because clinical deterioration may occur rapidly. 

Key Clinical Lessons 

This case reinforces several important principles for equine practitioners: 

• Mild colic signs can precede catastrophic haemorrhage 

• Serial ultrasonography is essential in monitoring progression 

• Persistent ovarian pain should not be ignored 

• Trends in TP, lactate, and heart rate are more valuable than isolated measurements 

• Bilateral ovarian enlargement is abnormal and warrants aggressive investigation 

Conclusion 

Haemoperitoneum remains a challenging diagnosis in equine practice because early clinical signs may be subtle. Pregnant mares presenting with recurrent colic, ovarian enlargement, and abdominal pain require close serial monitoring. 

This case demonstrates the importance of repeat ultrasonography, repeated abdominocentesis, and vigilant cardiovascular assessment in identifying progressive intra-abdominal haemorrhage before catastrophic decompensation occurs. 

References  

1. Sinovich M, Archer DC, Kane‐Smyth J, Scarabelli S, Ritchie A, Kelly PG. Haemoperitoneum associated with bilateral granulosa cell tumours in a pregnant mare treated by standing ovariectomy. Equine Veterinary Education. 2022 Dec;34(12):e526-32. https://beva.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/eve.13612  

2. Beachler TM, Bailey CS, McKelvey KA, Davis JL, Edwards A, Diaw M, Vasgaard JM, Whitacre MD. Haemoperitoneum in a pregnant mare with an ovarian haematoma. Equine Veterinary Education. 2016 Jul;28(7):359-63. https://doi.org/10.1111/eve.12211  

3. Sherlock CE, Lott‐Ellis K, Bergren A, Withers JM, Fews D, Mair TS. Granulosa cell tumours in the mare: A review of 52 cases. Equine Veterinary Education. 2016 Feb;28(2):75-82. https://doi.org/10.1111/eve.12449  

4. Worsman FC, Barakzai SZ, de Bont MP, Turner S, Rubio‐Martínez LM. Treatment of haemoperitoneum secondary to ruptured granulosa cell tumours in two mares. Equine Veterinary Education. 2020 Feb;32(2):71-7. https://doi.org/10.1111/eve.12929