Investigation of a novel, heritable bleeding diathesis of Thoroughbred horses and development of a screening assay.

This study investigates a unique, heritable bleeding disorder in Thoroughbred horses, describing its cellular physiology, providing a tool for diagnostic purposes, and demonstrating its inheritability. By observing a mare and her offspring, the researchers were able to identify a platelet secretion defect that causes a delay in thrombin production, leading to decreased clotting.

Research Objective and Methodology

• The goal of the study was to explore a specific defect in platelet secretion that is inheritable and leads to a reduction in thrombin generation, which in turn delays the process of blood clotting.
• The researchers used a total of three Thoroughbred horses – the affected mare and her offspring – for this study, all of whom were clinically normal otherwise.
• The investigators used washed platelets to examine their ability to perform several functions indicative of normal blood clotting. They observed the platelets’ ability to translocate phosphatidylserine, a membrane component, which was checked by annexin-V binding.
• The platelets’ ability to generate thrombin, a key enzyme in blood clotting, was assessed using the activity of the prothrombinase enzyme complex.
• The researchers also evaluated the platelets’ ability to bind fibrinogen, a protein crucial in the blood clotting process, and form aggregates, which were monitored through flow cytometry.

Results and Conclusion

• The platelets of the subject mare and her progeny could translocate phosphatidylserine, creating a procoagulant surface – a step crucial in the blood clotting process.
• The subject’s platelets demonstrated reduced prothrombinase activity, leading to less thrombin production compared to controls, which in turn results in decreased clotting.
• Both the subject mare and her offspring exhibited reduced fibrinogen binding when stimulated with thrombin, which possibly impacts the proper clotting of blood.
• The researchers concluded that the subject mare carries a heritable defect that impacts thrombin generation by activated platelets, leading to less clotting. This observation has potential applications in identifying horses with a similar condition and can provide valuable insights about bleeding disorders in horses.
• A flow cytometric assay of fibrinogen binding to washed platelets was developed that could help distinguish individuals with this specific platelet dysfunction. This tool could potentially be useful for detecting subclinical or acquired platelet dysfunctions in Thoroughbred horses.