Toxic effects of the vitamin K family are manifested mainly as hematological and circulatory derangements. Not only is species variation encountered, but profound differences are observed in the ability of the various vitamin K compounds to evoke a toxic response (Barash, 1978). The naturally occurring forms of vitamin K, phylloquinone and menaquinone, are nontoxic at very high dosage levels. The synthetic menadione compounds, however, have produced toxic effects when fed to humans, rabbits, dogs and mice in excessive amounts. The toxic dietary level of menadione is at least 1,000 times the dietary requirement (NRC, 1987). Menadione compounds can safely be used at low levels to prevent the development of a deficiency but should not be used to treat a hemorrhagic condition. The parenteral LD50 of menadione or its derivatives is 200 to 500 mg per kg of body weight in some species and dosages of 2 to 8 mg per kg body weight have been reported to be lethal in horses. Such data are not available for cattle (NRC, 1989).
