Sweet clover poisoning in cattle is caused by an anticoagulant (dicumarol) that is formed in moldy sweet clover hay. Previous experiments with vitamin K3 and vitamin K1 in therapy trials indicated that vitamin K1 was effective in reducing prothrombin times but vitamin K3 was not. As a possible alternative in the use of toxic sweet clover hays, vitamin K3 was evaluated to see if it would prevent hemorrhagic crises when fed to cattle consuming toxic sweet clover hay. Vitamin K3 levels of 0, 0.45, 4.5, 11, and 45 mg/kg body weight/day were fed to 173-235-kg steers consuming toxic (40-50 ppm dicumarol) sweet clover. The 45-mg K3/kg/day supplement was not palatable and had to be discontinued. The 0.45, 4.5, and 11-mg K3/kg/day supplements did not significantly reduce the prothrombin times as compared to the 0-mg K3/kg/day group.