Platelet function defect in a 5-day-old Simmental calf.

A 5-day-old Simmental Heifer was evaluated for excessive bleeding from the skin following horse fly bites. A coagulation profile and platelet numbers were normal. In vitro platelet function, measured by whole blood aggregometry, was found to be abnormal when compared with age-matched controls. Therefore, this defect in hemostasis was attributed to a qualitative defect in platelet function.