Blood clotting depends upon a cascade of reactions occurring in correct sequence. This cascade depends upon many factors. If any factor is missing, or deficient clotting is delayed, leading to bleeding. The most common cause of a blood clotting disorder in cats in warfarin (rat bait) poisoning. Clotting disorders are rare in dogs. The most common and best studied is Von Willebrand's Disease (vWD).
Von Willebrand's Disease
This inherited condition has been diagnosed in over 50 breeds. Although rare in all breeds other than the Doberman, where it is common but mild, if may cause severe, often fatal bleeding in affected young Scottish Terriers and Pembroke Welsh Corgis in particular. We diagnose by blood testing for vWD antigen and checking bleeding time. Bleeding is more severe in the young, causing unexpected bruising, nosebleeds or blood in the urine or faeces. We blood terst potentially affected individuals before any elective surgery.
Warfarin and other anticoagulant rodent poisons are dangerous to cats and dogs of any size. These cause vitamin K deficiency, leading to spontaneous bleeding. Newer anticoagulant rodent poisons are 100 times more toxic than warfarin. Blood transfusion may be needed for severe blood loss. In less threatening situations we use blood replacer fluids. Of course, a series of Vitamin K injections are always given.