Hemostatic Disorders

Primary bleeding disorders of the neonatal foal are relatively uncommon but may occasionally require investigation.

I. Normal Values

1. Platelet numbers similar to adults.

1. Significantly decreased function of platelets in foals in first 12 hours of life may predispose to platelet related bleeding [1].

2. Prothrombin time - (PT) & activated partial thromboplastin time (APPT) are slightly longer than adult.

1. PT 13.1 ± 0.3 sec (mean ± SD).
2. APTT 44.4 ± 2.4 sec (mean ± SD).

II. Inherited Defects

1. Hemophilia [2]

1. Documented in male Thoroughbreds, Standardbred, Arabian and Quarter horses.
2. Factor VIII deficiency.
3. Signs develop from 2 months to 3 years of age.
4. Diagnosis

1. Normal PT.
2. Prolonged APTT.
3. Low factor VIII activity.

5. Inherited as X-chromosome homozygous recessive

2. von Willebrand Disease [3]

1. Prolonged breeding noted at injections or wounds.
2. Prolonged activated partial thromboplastin time (APTT); normal PT. APTT findings are variable.
3. von Willebrand factor required for platelet adhesions and plug formation.
4. Need specific assay.
5. Is heritable - Test sire and dam.

3. Prekallikrein deficiency [4]

1. Prolonged bleeding with wounds.
2. Marked prolonged APTT, normal PT. APTT becomes normal with plasma added.
3. Belgian horses, is familial [6].

III. Disseminated Intravascular Coagulation [5,7]

1. A thrombotic and hemorrhagic disorder secondary to shock, septicemia, endotoxemia, viremia, renal disease, liver disease, peritonitis, pneumonia or post operative hemorrhage.
2. May present clinically as a thrombotic crisis or hemorrhagic diathesis.

1. Petechiation and ecchymoses on mucous membranes, nictating membrane, inner pinna of ear and retina.

3. Diagnosis - Presence of three of these four clinical pathologic findings.

1. Thrombocytopenia.
2. Elevated fibrin degradation products.
3. PT increased.
4. APTT increased.

4. Therapy

1. Correct primary disorder.
2. Use of systemic anticoagulants to inhibit consumptive process has not been evaluated in foals.
3. NSAID - Antiprostaglandin drugs to decrease platelet aggregation may be helpful but must be evaluated relative to their potential side effects in severely ill foals.

IV. Immune-Mediated Thrombocytopenic Bullous Pemphigoid [3,4]

This is a recently described disorder which is most likely an immune-mediated due to absorption of colostral immunoglobulins which contain antibodies against thrombocytes and possibly dermal components. Foals often have oral ulcers, crusty miliary skin, and on blood work leucopenia and thrombocytopenia, which can be very severe. It has been described in several different breeds including Quarter horse and Friesian.

Prevention

1. If a mare has previously produced one of these foals: if a similar repeat mating is done, withhold mare colostrum, provide alternative colostrum and treat as NI foal.
2. Mares at risk:
   Unknown.

Clinical Features

1. Foals born healthy, nurse, and then seen at 12-36 hrs for not nursing, lethargy, and inflammation of mouth, lips, nasal mucosa with ulceration and sometimes bleeding.
2. Biopsy of ulcers compatible with bullous pemphigus [1].

Laboratory Features

1. Thrombocytopenia - Very low (often <50000/μl)
2. May have leucopenia
3. PCV normal

Treatment

1. Dexamethasone, antimicrobials, nursing and supportive care.
2. Most foals will recover