There are several layers of understanding with vitamin K.  This vitamin was first discovered by Danish researcher Henrik Dam in 1929.  In his research with cholesterol in growing chicks, diets with fat removed resulted in extensive hemorrhages. Adding back cholesterol did not help, but there was another mysterious component which did, which was named Vitamin K—the Koagulation vitamin.  (Good thing vitamin K wasn’t discovered in an English-speaking lab, where the Vitamin C name was already taken, and “Coagulation” wouldn’t have made sense).  Also, this explains why all the letters between E (for vitamin E) and K were skipped in vitamin nomenclature.

The next layer of vitamin K understanding involves structure and nomenclature.  Phylloquinone, a substance prevalent in the diet (broccoli, spinach—Popeye was right!), received the name K1, is a fat soluble vitamin, and is relatively non-toxic.  In the gut, bacteria convert K1 into K2 (menaquinone), which is a little more biologically active than K1 and also has many interesting isomers with different sidechains.  Of these, several have nutritionally interesting functions; more on this later.  K3 (menadione) is the common supplemented form of vitamin K, which is absorbed as a pre-vitamin and converted into K2 in the body.

On to layer 3: biological functions.  As initially discovered, vitamin K (remember Koagulation?) regulates the cascade reaction of blood clotting factors through a specific protein reaction.  However, in addition to supporting blood clotting, certain Vitamin K isomers such as MK-4 (form of vitamin K produced by animals from supplemental K3), and MK-7, which regulates bone formation and eggshell mineralization through its action on osteocalcin and other proteins.  These reactions are very important in breeder/layer operations, and in young growing monogastrics.  In human medicine, MK-7 appears to encourage bone calcification while preventing calcification of blood vessels (“hardening of the arteries”) and appears to have a role in osteoporosis prevention.  Because MK-7 originates from bacterial metabolism of K2, dietary sources include fermented products such as cheese, sauerkraut, and soybean natto.

Layer 4 concerns supplemental sources and resulting analytics for vitamin K in livestock rations.  Commonly supplemented forms of K3 include menadione nicotinamide bisulfite (MNB: 43.9% menadione and 31.2% nicotinamide), menadione dimethyl-pyrimidinol bisulphite (MPB: 45.5% menadione), and menadione sodium bisulphite complex (MSBC: 33.9% menadione).  MSBC and MPB are both water soluble (MNB is not), and Vitamin K is generally thought to be the least stable of all the vitamins in a premix.  For lab analyses, feed and premix vitamin K assays are based on menadione content, so source listing is essential when comparing formulas.  Vitamin K regulations in feed are somewhat confusing; less so since AAFCO included Recommendations for Use of Menadione Sodium Bisulfite Complex (MSBC) in Animal Feed, in the Official Publication (OP) after convening a panel of experts in 2021, which permits MSBC as a vitamin K source for ALL species. MNB and MPB are permitted up to specific gram levels in US poultry and swine, and Table IV listings are available for Canadian livestock.  In the US for example, menadione from either MPB or MNB maximum levels are 874 mg/ton for poultry and 4370 mg/t for swine.