An outbreak of a haemorrhagic diathesis in cattle fed home produced hay is described. A similar syndrome was reproduced experimentally in calves by feeding them the hay. The experimental disease was characterised by increased prothrombin and partial thromboplastin times while the leucocyte and erythrocyte counts remained normal until the terminal haemorrhage. The calves ate well and grew well until the rapid onset of progressive weakness, stiff gait, mucosal pallor, tachycardia, tachypnoea and haematomata ending in sudden death. The absence of blood coagulation was seen at necropsy while petechial, ecchymotic and free haemorrhages were found in most organs. Particularly striking were massive ecchymotic haemorrhages on the peritoneal surface of the rumen, a bloody, gelatinous mass enveloping each kidney and extensive bruising, haemorrhage and haematomata in the subcutis of the limbs. In a second feeding trial the effects of various preparations of vitamin K1 and vitamin K3 were investigated. Oral administration of large quantities of vitamin K1 reduced the elevated prothrombin time; vitamin K3 acted less consistently. Analysis of the hay for trichothecene mycotoxins was negative but floral analysis revealed that sweet vernal grass (Anthoxanthum odoratum) comprised about 80 per cent of the hay. Dicoumarol was detected in the hay and in the serum and ruminal contents of the experimental calves. The diagnosis, treatment, control and importance of this syndrome in the United Kingdom are discussed.
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