A PRIMARY PLATELET DISORDER OF CONSANGUINEOUS SIMMENTAL CATTLE

A severe hereditary hemorrhagic diathesis in Simmental cattle has been identified in North America. Platelet numbers and -coagulation profil es of affected cattle are normal. We have further characterized the se vere dysfunction of platelet aggregation. All agonists tested elicited normal shape change. Aggregations in response to ADP, A23187, and col lagen were absent. Aggregations were decreased or required more time f or completion in response to PAF and thrombin. No ultrastructural abno rmalities were observed in transmission electron micrographs. Dense gr anule release of ATP in response to PAF was normal. Thrombin-induced a ggregation was dependent upon external calcium concentration in normal but not affected animals. Clot retraction in the blood from affected animals was abnormal. The data implicate a defect of Ca++ mobilization or utilization.