Why Do Greyhounds Bleed? (But Some Clot)?
With the increasing popularity of retired rescued Greyhounds, veterinarians are likely to evaluate dogs of this breed more frequently in their practice. It is estimated that approximately 120,000 Greyhounds lived in homes as pets, compared to 55,000 Greyhounds in racetracks. In the past few years, private Greyhound adoptions ranged from 15,000 to 18,000/year (Gary Guccione, National Greyhound Association, personal communication).
Therefore, it is important that they recognize the physiological peculiarities of this breed. For instance, mean packed cell volume (PCV), hemoglobin concentration, red blood cell count, and whole blood viscosity are higher, while white blood cell, neutrophil, and platelet counts are lower in Greyhounds than in other breeds. In addition, serum creatinine concentrations and liver transaminase activities are higher than in non-Greyhound dogs.
In the Greyhound community, the term Greyhound bleeder is typically used for dogs that bleed either spontaneously or 1-2 days after minor trauma or a simple surgical procedure. Most of the dogs with bleeding diathesis have normal one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), and platelet counts.
Greyhounds are not one of the breeds with a reported high prevalence of von Willebrand disease (VWD). However, in a recent 2-year review period (7/2002 to 7/2004) approximately 10% (22 of 216) of the Greyhounds screened at the Comparative Coagulation Section had plasma VWF concentration of < 30%.Therefore, it is unlikely that VWD is responsible for the perioperative bleeding in Greyhounds.
We have been evaluating hemostasis in Greyhounds for the past 5 years, and determined that approximately 26% of retired racers will bleed 36-48 hours after a spay or neuter procedure (Lara); despite this, all the hemostatic parameters we evaluated, including OSPT, APTT, fibrinogen concentration, VWF activity and function (i.e.; collagen binding assay), platelet function using the PFA-100, fibrinolysis, antithrombin activity, clot lysis ad retraction, clot stabilization, and D-dimer concentration were not different between bleeders and nonbleeders, nor did they allow for preoperative identification of bleeders.
The thrombelastograph (TEG®) is a whole blood coagulation analyzer, so cell/protein interaction can be evaluated; it allows for a global analysis of the hemostatic system, including primary and secondary hemostasis, and the fibrinolytic system. The TEG® is a novel device in veterinary medicine used to evaluate patients with coagulopathies. We recently evaluated a large number of Greyhounds using this methodology, and published reference ranges for the breed.
Our data supports the fact that “bleeders” are not able to increase the clot strength postoperatively, as the “nonbleeders” and other non-Greyhound dogs do. We recently demonstrated that a procoagulant (epsilon aminocaproic acid-EACA or Amicar®), at dosages of 500-1,000 mg, PO or IV, q8h, for 5 days, starting in the immediate postoperative period, significantly decreases the severity and frequency of bleeding in Greyhounds undergoing limb amputation for bone cancer and after spays/neuters.
We are also actively working on the issue of thrombosis and thromboembolism in Greyhounds. We have recognized aortic, iliac, or femoral thrombosis as a cause of intermittent lameness in Greyhounds, and also identified the fact that retired racers are at high risk for CNS thromboembolic events. The latter are peracute, and may affect the brain or spinal cord causing severe neurologic signs. It appears that mini-dose aspirin (1/4-1/2 cardio aspirin once a day) results in rapid, marked clinical improvement in these patients.
MRI OF 10 YEAR OLD GREYHOUND WITH PERACUE ATAXIA. NOTE AREA OF INFARCTION.
C. Guillermo Couto, DVM, dipl. ACVIM
Couto Veterinary Consultants
Hilliard, OH 43026
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Vilar Saavedra P, Couto CG, Iazbik, MC, Westendorf N, Charske J, Marín LM. Thromboelastographic tracings in retired racing Greyhounds and in non-Greyhound dogs. J Vet Intern Med 2008; 22:374–379.