Vitamin K

Vitamin K is a fat-soluble vitamin essential for blood clotting, earning the name antihaemorrhagic vitamin because it lets the liver manufacture several of the coagulation factors. Part of a dog's and cat's requirement is met by bacteria in the gut, which synthesise vitamin K, so spontaneous dietary deficiency is uncommon in healthy animals on a complete diet. Several forms exist: vitamin K1, or phylloquinone, from plants; vitamin K2 of microbial origin; and menadione, or K3, a synthetic water-soluble form used in some foods, often listed as menadione sodium bisulphite among the additives. FEDIAF sets a minimum vitamin K level mainly for cats and for fish-rich diets, where availability may be reduced (FEDIAF, 2021). The most important clinical point is that the commonest cause of a functional vitamin K problem is not dietary at all but toxic: anticoagulant rodenticides, the active ingredients of many rat and mouse poisons, work precisely by blocking the vitamin K cycle, causing severe and potentially fatal internal bleeding that is treated with vitamin K1 as the antidote. Deficiency shows as prolonged bleeding and easy bruising. Dietary sources include liver, leafy green vegetables and certain oils. On a label it appears among the added vitamins. See the [Petipedia glossary](/glossary) for related fat-soluble vitamins.

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