Bleeding Disorders in Horses: Types, Signs & Treatment

Bleeding disorders can significantly affect your horse’s performance and overall health. These conditions can be present from birth or develop later in life and are characterized by abnormal bleeding or hemorrhage. ^[1]

Some bleeding disorders, such as exercise-induced pulmonary hemorrhage (EIPH), are very common and manageable while others are rare and poorly researched in horses. ^[2]

A coagulation disorder may be present if the horse has prolonged or excessive bleeding following trauma. Other signs of bleeding disorders include frequent nosebleeds, coughing, exercise intolerance, excessive bruising, increased respiratory effort and blood in respiratory secretions.

With prompt intervention, many bleeding disorders can be treated effectively. Due to the risk of complications, caution should be taken when performing surgery or castration on a horse with a bleeding disorder. ^[2]

Understanding how bleeding disorders impact your horse can help you manage the condition and improve your horse’s prognosis. If you suspect your horse or foal could have a bleeding disorder, consult with your veterinarian to obtain a diagnosis.

Bleeding Disorders in Horses

When a horse experiences internal or external bleeding due to trauma or another event, the body activates a crucial process known as hemostasis. Hemostasis serves to arrest the flow of blood and prevent further injury or complications. ^[1]

Hemostasis is a finely coordinated process involving blood vessels, platelets and blood clotting proteins as part of the coagulation cascade. This complex series of events triggered by blood vessel damage, is responsible for the formation of a stable blood clot to effectively stop bleeding. ^[2]

The coagulation cascade is tightly regulated to prevent excessive clotting or bleeding. It involves a delicate balance of pro-coagulant and anti-coagulant mechanisms working together to achieve hemostasis.

Disruptions in this balance can lead to a variety of bleeding disorders or thrombotic conditions in horses. Some of the most common equine bleeding disorders are discussed in further detail below.

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Exercise-Induced Pulmonary Hemorrhage (EIPH)

Exercise-induced pulmonary hemorrhage describes hemorrhage or bleeding in the horse’s lungs, particularly during intense exercise. It is estimated that 44 – 75% of Thoroughbreds and up to 87% of Standardbreds are affected by EIPH. ^[2]

EIPH is linked to elevated blood pressure in the fragile pulmonary blood vessels during strenuous activity. While the exact mechanism is not fully understood, several factors are believed to contribute to EIPH, including: ^[3]

• Frequent high intensity or prolonged exercise
• Increased stress on the lungs due to repeated expansion and contraction
• Pulmonary capillary stress failure (rupture of small blood vessels in the lungs)
• Respiratory inflammation linked to conditions, such as recurrent airway obstruction (RAO)

Excessive bleeders or nosebleeds in exercising horses immediately raises suspicion of EIPH, which can sometimes cause the diagnosis of other bleeding disorders to be missed.

However, horses with an underlying condition, such as poor blood clotting or platelet dysfunction, sometimes develop secondary EIPH. ^[2] Consequently, horses may receive treatment for EIPH without addressing the underlying primary disorder that causes the bleeding.

Inherited Clotting Protein Disorders

Some inherited bleeding disorders are attributed to abnormalities or deficiencies in specific blood clotting proteins.

These genetic conditions impair the horse’s ability to form blood clots effectively, leading to an increased risk of bleeding or difficulty in stopping bleeding.

Hemophilia A (Factor VIII deficiency)

Equine hemophilia A is a genetic condition caused by a deficiency of clotting factor VIII (FVIII), which is a protein essential for the formation of blood clots. This defective gene is recessive and located on the X-chromosome. ^[1][4]

Female horses have two copies of the X-chromosome. They can act as carriers of hemophilia A without being directly affected by the disorder themselves. In contrast, males have only one X-chromosome. Therefore, those who inherit the gene associated with hemophilia A will have symptoms of the condition.

Severe deficiencies of Factor VIII hinder hemostasis. Affected colts and geldings may exhibit spontaneous bleeding, prolonged bleeding after trauma, or excessive bleeding during surgery. Even minor injuries can produce bleeding that lasts for a long time.

Swelling and lameness can occur if the horse bleeds into its joints or muscles. Severe or fatal internal hemorrhaging may occur into the chest cavity.

Diagnosing this condition in foals under 6 months of age is challenging due to inadequate production of clotting proteins at this early stage. ^[1][2]

Von Willebrand Disease

Von Willebrand Disease (vWD) is a rare inherited bleeding disorder that is typically present from birth. It is caused by a deficiency or dysfunction of von Willebrand factor (vWF), a protein involved in platelet adhesion and clot formation. This genetic disease is reported in Quarter horses and Thoroughbreds. ^[1][5]

Defects in the function of von Willebrand factor impair the horse’s ability to form blood clots. Affected horses may have spontaneous bleeding from mucosal surfaces or experience excessive bleeding following trauma or surgery.

Other clinical signs associated with von Willebrand disease include: ^[6][7]

• Lethargy
• Anemia
• Rapid, shallow breathing (tachypnea)
• External hemorrhage (nose, mouth)
• Internal hemorrhage (urinary tract, gastrointestinal, subcutaneous)
• Fever

Von Willebrand Disease is diagnosed by collecting and analyzing a blood sample. Low levels of von Willebrand factor in the blood plasma indicate the presence of vWD.

Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is a rare genetic condition that affects normal platelet function. It is caused by a defect in the glycoprotein IIb-IIIa complex, which is responsible for platelet aggregation and clot formation. ^[8]

While horses with GT tend to have normal platelet counts, some platelets may be large and malformed. As a result, platelets are unable to adhere to each other or to the blood vessel walls, leading to impaired clot formation and prolonged bleeding.

GT has been reported in several breeds, including Thoroughbred crosses, Quarter horses and Oldenburgs.

Horses with Glanzmann thrombasthenia typically present with spontaneous nosebleeds that are not associated with exercise. ^[1] In addition to nosebleeds, affected horses exhibit the following symptoms. ^[8][9]

• Extensive bruising
• Purpura or petechiae (small purple dots on the skin)
• Bleeding of the gums

A diagnosis of Glanzmann thrombasthenia is usually made early on in the horse’s life based on clinical signs genetic testing, and flow cytometry (FC). FC is a a technique used to analyze the size and shape of cells or particles in a liquid solution. ^[8]

While there is no treatments available for GT, blood transfusions may be administered in cases of extended bleeding. Medications that can interfere with clotting should not be used in horses with GT due to a risk of complications. ^[1]

Prekallikrein Deficiency

Prekallikrein, or Fletcher factor, is a glycoprotein involved in the coagulation cascade and the formation of blood clots. It activates other clotting factors to help form a stable blood clot following injury. ^[2]

Prekallikrein deficiency is characterized by the insufficient production or dysfunction of this clotting factor, impairing the horse’s clotting ability.

This can lead to prolonged and excessive bleeding after injury or surgery, and increased susceptibility to bruising or hematoma formation. However, some affected horses have no symptoms.

This genetic condition is believed to follow an autosomal recessive inheritance pattern. This means that in order for an individual to have the condition, they must inherit two copies of the defective gene, one from each parent. Horses who inherit only one copy of the gene are considered carriers and typically do not exhibit symptoms of prekallikrein deficiency. ^[10][11]

Prekallikrein deficiency is very rare and has only been documented in one Belgian horse and one miniature horse family. ^[10][11]

Currently, there is no known cure for prekallikrein deficiency in horses. Management strategies aim to minimize bleeding episodes and maintain the horse’s overall health.

Acquired Clotting Protein Disorders

While some clotting protein disorders are genetically determined and present from birth, other conditions develop later in life, due to illness, medication use, nutritional deficiency or other external factors.

In the following section, we discuss some of the most common acquired clotting disorders that cause an increased risk of bleeding or abnormal clot formation.

Disseminated Intravascular Coagulation (DIC)

Disseminated Intravascular Coagulation (DIC) in horses is a complex and potentially life-threatening condition characterized by abnormal and excessive blood clotting throughout the body’s blood vessels. ^[1] This condition can result in impaired blood flow, tissue damage, organ dysfunction and even organ failure. ^[12]

DIC occurs as a result of an underlying disease or condition that triggers a complex cascade of events, leading to the widespread activation of the clotting system.

The body’s reserves of clotting factors and platelets are consumed and depleted during this process, disrupting the delicate balance required to maintain hemostasis. Normal clotting function is compromised and affected horses may develop spontaneous bleeding.

DIC is a serious condition that can be fatal for horses without intervention. Prompt identification and treatment of the underlying illness is critical to maintain proper circulation. Failure to intervene may result in extensive blood clot formation or compromised circulation, leading to potential death.

Affected horses should be stabilized with intravenous (IV) fluids, anti-endotoxin medication and anti-inflammatory drugs to support healing and minimize complications associated with this complex disorder. ^[13]

Platelet Disorders

Platelets, or thrombocytes, are important blood components that are essential for maintaining hemostasis. These irregularly shaped cell fragments are formed in bone marrow, primarily from megakaryocytes. ^[14]

When there is damage to blood vessels, platelets are activated to help stop the bleeding. They adhere to the collagen fibers in injured blood vessel walls, forming a temporary plug to prevent bleeding.

Platelets also release various substances, such as clotting factors, to initiate the coagulation cascade, which leads to the formation of a stable blood clot. This clot helps seal the damaged blood vessel and allows for wound healing and protection from infection.

Platelet disorders occur when there is an excess, deficiency, or abnormalities in platelet count or function. These disorders can manifest in various ways and may be caused by genetic factors, acquired conditions, or underlying medical conditions.

Platelet disorders can be classified into two main types: qualitative and quantitative. Qualitative platelet disorders are characterized by physical or functional abnormalities in the platelets, regardless of whether platelet counts are within the normal range. ^[9]

Quantitative platelet disorders occur when there are either too many (thrombocytosis) or not enough (thrombocytopenia) platelets in the body. Low platelet counts can lead to excessive bleeding, whereas high platelet counts can cause excessive clotting.

If you suspect your horse may have a platelet disorder, consult with your veterinarian. They will be able to guide you through the diagnostic process and develop an appropriate treatment plan.

Thrombocytopenia
Thrombocytopenia is characterized by a low platelet count in the blood. This condition can occur due to various underlying causes and can have significant implications for the horse’s health.

Horses can develop thrombocytopenia due to immune system dysfunction (idiopathic) or as a result of anti-coagulant drug administration. ^[1]

The prognosis for thrombocytopenia depends on the successful treatment of the primary disease or condition resulting in the low platelet count. ^[15]

Immune-Mediated Thrombocytopenia
Immune-mediated, or idiopathic, thrombocytopenia (IMT) occurs when the body makes antibodies that destroy platelets in the horse’s bone marrow, reducing the number of platelets in the blood. While rare, there have been documented cases in horses.

Clinical signs of thrombocytopenia in horses include the following: ^[1]

• Severe bleeding
• Purpura or petechiae (small purple dots on the skin or gums)
• Swelling in the legs
• Prolonged bleeding after venipuncture (blood collection)
• Nosebleeds (epistaxis)
• Dark, sticky stools (melena)
• Bleeding within the eye (hyphema)
• Fever

The diagnosis of immune-mediated thrombocytopenia involves a thorough physical examination, complete blood count (CBC) to assess platelet levels, and laboratory tests to rule out other causes of thrombocytopenia. The detection of platelet-bound antibodies or evidence of immune-mediated destruction of platelets supports the diagnosis of IMT.

Treatment for IMT involves suppressing the horse’s immune response and increasing platelet production in the body. This is typically accomplished by administering corticosteroids or other immunosuppressant medications. ^[1]

Consult with a veterinarian if you suspect IMT in your horse. Early diagnosis and treatment can significantly improve the outcome and prevent further complications associated with thrombocytopenia.
Drug-Induced Thrombocytopenia (DIT)
Certain medications or veterinary treatments can decrease the horse’s platelet count, impairing the ability to form blood clots.

Medications that can induce thrombocytopenia in horses include:

• Antibiotics such as penicillin
• Non steroidal anti-inflammatory drugs (NSAIDs)
• Sulfonamides
• Erythromycin
• Heparin
• Quinidine

The mechanism by which these drugs cause thrombocytopenia varies. ^[1][16] Note that cases of thrombocytopenia following use of these medications is rare, and most horses tolerate these drugs without any adverse effects on platelet count.

Treatment for drug-induced thrombocytopenia primarily involves discontinuing the medication and providing supportive care. By discontinuing the drug responsible for DIT, the horse’s body can undergo a natural recovery process to restore platelet levels.

Consult with your prescribing veterinarian if your horse shows signs of drug-induced thrombocytopenia.

Blood Vessel Disorders

Some equine bleeding disorders involve conditions affecting the structure, function, or integrity of blood vessels throughout the horse’s body.

These disorders can arise from various causes, including genetic factors, inflammation, injury, or underlying medical conditions. Examples of blood vessel disorders in horses include the following:

Ehlers-Danlos Syndrome

Ehlers-Danlos syndrome (EDS), or cutaneous asthenia, is a rare genetic disorder that affects the connective tissues of the body, including blood vessels.

Collagen is an important protein that provides structural support and elasticity to connective tissue. Horses with EDS have a type 1 collagen defect, affecting the production, formation and stability of collagen fibers in blood vessels. ^[1]

EDS horses can be further classified into specific subtypes, two of which are Warmblood Fragile Foal Syndrome type 1 (WFFS) and hereditary equine regional dermal asthenia (HERDA).

WFFS is typically only seen in warmbloods, while HERDA is usually seen in stockier breeds, such as Quarter horses, American Paint horses and Appaloosas.

Affected horses have weak blood vessels leading to various clinical manifestation, including clotting and excessive bruising in the body. This condition results in hyperextensible (extra stretchy) and fragile skin that is prone to easy tearing.

Depending on the severity, horses with EDS may exhibit mushy or soft skin upon touch, along with hyper-flexible joints that and an increased range of motion. ^[17]

Hypercoagulability (Excessive Blood Clotting)

Hypercoagulability is a condition characterized by increased coagulation activity within the blood, leading to a higher likelihood of clot formation.

These blood clots have the potential to dislodge and travel through the bloodstream, causing blockages in smaller arteries along their course. ^[1]

Excessive blood clotting may develop secondary to a systemic inflammatory condition, such as colic or laminitis. Hypercoagulability can also be triggered by ingestion of poisonous substances or an infection that destroys platelets. ^[5]

Hypercoagulability is typically diagnosed based on the presence of clinical signs, the horse’s medical history and laboratory tests. The following signs could indicate excessive clotting:

• External or internal hemorrhage (bleeding)
• Small red dots (petechiations) or bruising (ecchymoses) on the mouth and ears
• Fast heart rate (tachycardia)
• Lethargy & weakness
• Food avoidance & anorexia

Prognosis

The prognosis for horses with bleeding disorders depends on type and severity of the disorder, underlying cause, and response to treatment.

Some disorders can be effectively managed with appropriate treatment and supportive care, allowing affected horses to lead relatively normal lives.

However, other bleeding disorders have a more guarded prognosis due to the risk of severe bleeding or life-threatening complications Conditions such as von Willebrand Disease, Glanzmann thrombasthenia, or severe platelet disorders can pose significant challenges in terms of bleeding control and long-term management.

If your horse is showing signs of abnormal or excessive blee Regular monitoring, appropriate ongoing care, and prompt intervention during bleeding episodes are essential for improving your horse’s prognosis.