Hemostatic indices were determined in 45 healthy light breed foals, from birth to 1 month of age, and in 20 healthy adult (>2 years of age) light breed horses. Blood samples were obtained from each foal at 4 ages: 1) < 24 hours, 2) 4-7 days, 3) 10-14 days, and 4) 25-30 days. The following hemostatic indices were determined: platelet count; prothrombin and activated partial thromboplastin times; activity concentrations of protein C, antithrombin III, plasminogen, alpha-2 antiplasmin, tissue plasminogen activator, and plasminogen activator inhibitor- 1; plasma protein C antigen and fibrinogen concentrations; and serum fibrin degradation products concentration. Prothrombin and activated partial thromboplastin times were significantly longer at birth than in older foals. The plasma concentrations of the following were significantly lower at birth than in older foals: antithrombin III, plasminogen and tissue plasminogen activator activities, protein C antigen, and fibrinogen. Concentrations of the following were significantly higher at birth than in older foals: protein C and plasminogen activator inhibitor-1 activities and fibrin degradation products. These results indicate that hemostatic indices of neonatal foals differ significantly from those of older foals and adults. With the exceptions of antithrombin III and tissue plasminogen activator activities, all hemostatic indices measured in foals at 1 month of age were equivalent to adult values.
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