Vitamin K

Properties and Metabolism

The generic term vitamin K is now used to describe not a single chemical entity, but a group of quinone compounds that have characteristic anti-hemorrhagic effects and are fat soluble. The basic molecule is a naphthoquinone, and the various isomers differ in the nature and length of the side chain. Vitamin K extracted from plant material was named phylloquinone or vitamin K1 (Illus. 5-1). Vitamin K-active compounds from material that had undergone bacterial fermentation were named menaquinones or vitamin K2. The simplest form of vitamin K is the synthetic menadione (K3), which has no side chain. Menaquinone-4 is synthesized in the liver from ingested menadione or changed to a biologically active menaquinone by intestinal microorganisms. Rumen microorganisms synthesize large quantities of vitamin K2, and the vitamin K content of cow’s milk is reportedly 10 times higher than that of monogastric species.

Properties and Metabolism

Illustration 5-1

Vitamin K1 is a golden yellow, viscous oil. Naturally occurring sources of vitamin K are fat soluble; stable to heat; and is destabilized by oxidation, alkali conditions, strong acids, light and irradiation. Vitamin K1 is slowly degraded by atmospheric oxygen, but fairly rapidly destroyed by light. In contrast to naturally occurring sources of vitamin K, vitamin K3salts of menadione are water soluble.Vitamin K antagonists increase the need for this vitamin. Deficiency of this vitamin is produced by ingestion of the antagonist, dicumarol, or by feeding of sulfonamides (in monogastric species) at levels sufficient to inhibit intestinal synthesis of vitamin K. Supplementation of vitamin K will overcome the anticoagulation effect of dicumarol. Mycotoxins are also antagonists that may cause vitamin K deficiency.Like all fat-soluble vitamins, vitamin K is absorbed in association with dietary fats and requires the presence of bile salts and pancreatic juice for adequate uptake from the alimentary tract. Absorption of vitamin K depends on its incorporation into mixed micelles, and optimal formation of these micellar structures requires the presence of both bile and pancreatic juice. Thus, any malfunction of the fat absorption mechanism (e.g., biliary obstruction) reduces availability of vitamin K (Ferland, 2006). Unlike phylloquinone and the menaquinones, menadione salts are relatively water soluble, and, therefore, are absorbed satisfactorily from low-fat diets. Male animals are more susceptible to dietary vitamin K deprivation than females, apparently as a result of a stimulation of phylloquinone absorption by estrogens; the administration of estrogens increases absorption in both male and female animals (Jolly et al., 1977).

The lymphatic system is the major route of transport of absorbed phylloquinone from the intestine. Shearer et al.(1970) demonstrated the association of phylloquinone with serum lipoproteins, but little is known of the existence of specific carrier proteins. Ingested phylloquinone is absorbed by an energy-dependent process from the proximal portion of the small intestine (Hollander, 1973). In contrast to the active transport of phylloquinone, menaquinone is absorbed from the small intestine by a passive noncarrier-mediated process.

The measured efficiency of vitamin K absorption ranges from 10% to 70%, depending on the form of the vitamin administered. Some reports have indicated that menadione is completely absorbed, but phylloquinone is absorbed only at a rate of 50%. The complete absorption of menadione may be due to aqueous solubility of the menadione salts. Rats were found to excrete about 60% of ingested phylloquinone in the feces within 24 hours of ingestion, but only 11% of ingested menadione (Griminger and Donis, 1960; Griminger, 1984). However, 38% of ingested menadione, but only a small amount of phylloquinone, was excreted via the kidneys during the same period. The conclusion was that although menadione is well absorbed, it is poorly retained, while the opposite is true for phylloquinone. Normal human subjects were found to excrete less than 20% of a large (1 mg) dose of phylloquinone in feces, but as much as 70%-80% of the ingested phylloquinone was excreted unaltered in the feces of patients with impaired fat absorption caused by obstructive jaundice, pancreatic insufficiency or adult celiac disease. (Suttie, 2007).

Griminger and Brubacher (1966) showed that a major portion of the phylloquinone fed to chicks was absorbed and deposited in the liver intact. As such, it had equally as good biological activity upon prothrombin synthesis as menaquinone found in the chick’s liver following feeding of menadione. Therefore, menaquinone is most likely produced if menadione is fed or if the intestinal microorganisms degrade the dietary K1 or K2 to menadione. Formation of menaquinone is not required for metabolic activity of vitamin K, since phylloquinone is equally active in synthesis of the vitamin K-dependent, blood-clotting proteins (Scott et al., 1982).

A number of studies have shown that phylloquinone is specifically concentrated and retained but menadione is poorly retained in the liver. Menadione is found to be widely distributed in all tissues and to be very rapidly excreted. Although phylloquinone is rapidly concentrated in liver, it does not have a long retention time in this organ (Thierry et al., 1970). The inability to rapidly develop a vitamin K deficiency in most species results, therefore, from the difficulty in preventing absorption of the vitamin from the diet or from intestinal synthesis rather than from a significant storage of the vitamin. Some breakdown products of vitamin K are excreted in the urine. One of the principal excretory products is a chain-shortened and oxidized derivative of vitamin K, which forms gamma-lactone and is probably excreted as a glucuronide.


Vitamin K dependent proteins can be identified by γ-carboxyglutamic acid residues (Gla): this amino acid is common to all vitamin K proteins. Discovery of this new amino acid clarified the role of vitamin K in blood coagulation and led to the discovery of additional vitamin K-dependent proteins (e.g., bone proteins) (Ferland, 2006; Suttie, 2007). Coagulation time of blood is increased when vitamin K is deficient because the vitamin is required for the synthesis of prothrombin (factor II). Plasma clotting factors VII (proconvertin), IX (Christmas factor) and X (Stuart-Prower factor) also depend on vitamin K for their synthesis. These four blood-clotting proteins are synthesized in the liver in inactive precursor forms and then converted to biologically active proteins by the action of vitamin K (Suttie and Jackson, 1977). In deficiency, administration of vitamin K brings about a prompt response in four to six hours. In the absence of the liver, this response does not occur.

Bleeding disorders result from an inability of a liver microsomal enzyme, currently called the vitamin K-dependent carboxylase (Esmon et al., 1975), to carry out the normal post-translational conversion of specific glutamyl residues in the vitamin K-dependent plasma proteins to gamma-carboxyglutamyl residues (Nelsestuen et al., 1974). The result of insufficient vitamin K to serve as a cofactor for this enzyme is, therefore, a decrease in the rate of thrombin generation.

The action of converting inactive precursor proteins to biologically active forms involves the carboxylation of glutamic acid residues in the inactive molecules. Carboxylation allows prothrombin and the other procoagulant proteins to participate in a specific protein-calcium phospholipid interaction that is a necessity for their biological role (Suttie and Jackson, 1977). Four other vitamin K-dependent proteins have also been identified in plasma (i.e., proteins C, S, Z and M). Protein C and protein S play an anticoagulant rather than a procoagulant role in normal hemostasis (Suttie and Olson, 1990). Protein C inhibits coagulation, and, stimulated by protein S, it promotes fibrinolysis. Also, a protein C-S complex can partially hydrolyze the activated factors V and VIII and thus inactivate them. Protein S also has the potential to be involved in the regulation of bone turnover (Binkley and Suttie, 1995). Function for proteins M and Z is unclear. Protein Z has been shown to have an anticoagulant function under some conditions (Suttie, 2007).

The blood clotting mechanism can apparently be stimulated by either an intrinsic system, in which all the factors are in the plasma, or an extrinsic system. In the extrinsic system of coagulation, tissue thromboplastin, in the presence of various factors and calcium, converts prothrombin in the blood to thrombin. The enzyme thrombin facilitates the conversion of the soluble fibrinogen into insoluble fibrin. Fibrin polymerizes into strands and enmeshes the formed elements of the blood, especially the red blood cells, to form the blood clot (Griminger, 1984). The final active component in both the intrinsic and extrinsic systems appears to activate the Stuart factor, which in turn leads to activation of prothrombin. The various steps involved in blood clotting are presented in Figure 5-1. The action of vitamin K is required at four different sites in these reactions.

Figure 5-1: The Mechanism of Blood Clotting

Adapted from Scott et al., (1982) and McDowell (1989).

Continuing research has revealed that vitamin K-dependent reactions are present in most tissues and not just blood, and that a reasonably large number of proteins are subjected to this post-translational carboxylation of specific glutamate residues to gamma-carboxyglutamate residues (Vermeer, 1986). Atherocalcin is a vitamin K-dependent protein in atherosclerotic tissue. A vitamin K-dependent carboxylase system has been identified in skin, which may be related to calcium metabolism in skin (de Boer-van den Berg et al., 1986). Two of the best characterized vitamin K-dependent proteins not involved in hemostasis are osteocalcin or bone Gla protein (BGP) and matrix Gla protein, which were initially discovered in bone. Osteocalcin is a protein containing three Gla residues that give the protein its mineral-binding properties. Osteocalcin appears in embryonic chick bone and rat bone matrix at the beginning of mineralization of the bone (Gallop et al., 1980). It accounts for 15% to 20% of the non-collagen protein in the bone of most vertebrates and is one of the most abundant proteins in the body. Osteocalcin is produced by osteoblasts, with synthesis controlled by 1,25-dihydroxy vitamin D. About 20 percent of the newly synthesized protein is released in the circulation and can be used as a measure of bone formation. Matrix Gla protein-deficient mice have abnormal calcification leading to osteopenia, fractures and premature death owing to arterial calcification (Booth and Mayer, 1997). 

As is true for other non-blood vitamin K-dependent proteins, the physiological role of osteocalcin remains largely unknown. However, reduced osteocalcin content of cortical bone (Vanderschueren et al., 1990) and alteration of osteocalcin distribution within osteons (Ingram et al., 1994) are associated with aging. It remains unknown whether any of these findings are related to the age-related increased risk of fracture. Osteocalcin may play a role in the control of bone remodeling because it has been reported to be a chemoattractant for monocytes, the precursors of osteoclasts. Serum osteocalcin has been shown to be a good predictor of bone turnover in pigs (Carter et al., 1996). This suggests a possible role for osteocalcin in bone resorption (Binkley and Suttie, 1995).

Several reports have indicated that warfarin treatment alters the functional properties of bone particles prepared from rats. However, vitamin K-deficient chick embryos were able to mobilize sufficient quantities of calcium for normal skeletal development, although they exhibited severe reduction in blood clotting and bone osteocalcin concentration (Lavelle et al., 1994).

Observations that vitamin K could be involved in the pathogenesis of bone mineral loss have been summarized (Binkley and Suttie, 1995; Cashman and O’Connor, 2008): (1) low blood vitamin K in patients with bone fractures; (2) concentration of circulating under gamma-carboxylated osteocalcin associated with age, low bone mineral density and hip fracture risk; (3) anticoagulant therapy associated with decreased bone density and (4) decreased bone loss and calcium excretion with Vitamin K supplementation.

Both in vitro and in vivo studies to date suggest a role of vitamin K in the regulation of multiple enzymes involved in sphingolipid metabolism within the myelin-rich regions in the brain (Denisava and Booth, 2005). The brain is enriched with sphingolipids, which are important membrane constituents and major lipid signaling molecules that have a role in motor and cognitive behavior.

There is evidence that vitamin D functions in the distal renal tubules to improve calcium reabsorption and is mediated by the calcium-binding protein, calbindin (Bronner and Stein, 1995). It is known that 99% of the renal-filtered calcium is reabsorbed in the absence of vitamin D and PTH. The remaining 1% is under control of these two hormonal agents, although it is not known whether they work in concert. It has been shown that 1,25-(OH)2D functions in improving renal reabsorption of calcium (Sutton and Dirks, 1978).


The dietary vitamin K requirement for poultry suggested by the National Research Council (NRC, 1994) ranges from 0.4 to 1.75 mg per kg (0.2 to 0.80 mg per lb). When birds are fed a practical diet without any stress agents, the minimum requirement can often be met with as little as 0.6 mg per kg (0.27 mg per lb) of diet. However, if coccidiosis is a problem or other factors are present that can result in reduced intestinal synthesis or absorption, much higher levels are required (Leeson and Summers, 2001). Young growing turkeys, breeding turkeys and Japanese quail have the highest requirement of 1 to 1.75 mg per kg (0.45 to 0.80 mg per lb). Vitamin K requirements of poultry are met by a combination of dietary intake and limited microbial biosynthesis in the gut. Animals that practice coprophagy, such as the rabbit, can utilize much of the vitamin K that is eliminated in the feces. In rats, the majority of menaquinone (vitamin K2) absorbed resulted from fecal ingestion compared to dietary sources or from direct synthesis and absorption from the intestine (Kindberg et al., 1987). Contrary to most animals, poultry have a limited ability for intestinal synthesis, and so adequate dietary supplies are of greater importance. Poultry have a shorter digestive tract for vitamin K synthesis, with a rate of passage faster than for other species (McDowell, 2000). Chicks were also found to have less hepatic vitamin K epoxide reductase (Will et al., 1992). Activity of this enzyme in chicks was about 10% of that in rats fed the same diets; the inability of chicks to effectively recycle the epoxide of vitamin K (phylloquinone 2,3 epoxide) seems to be a major factor in their high requirement for the vitamin (Suttie, 2007). Because of microbial synthesis, a precise expression of vitamin K requirements is not feasible. The daily requirement for most animal species falls in the range of 2 to 200 µg vitamin K per kg (0.9 to 91 µg per lb) of body weight. It should be remembered that this requirement can be altered by age, sex, strain, anti-vitamin K factors, disease conditions and any condition influencing lipid absorption. The requirements of poultry for vitamin K are based upon blood clotting responses and there is no information on amounts of vitamin K needed for bone growth. Vitamin K may possibly play a beneficial role in osteoporosis. It is involved in the formation of osteocalcin, a matrix protein associated with bone formation. Dietary supplementation with additional vitamin K during the laying period did not affect osteoporosis (Rennie et al., 1997) or bone mineralization in chicks (Rodrigues et al., 1996). Lavelle et al. (1994) have reported that reduction in skeletal osteocalcin does not impair initial bone development in chicks but there is no information on whether provision of vitamin K above normal amounts may stimulate bone growth over the full rearing period.


There are two major natural sources of vitamin K, phylloquinones (vitamin K1) in plant sources and menaquinones (vitamin K2) produced by bacterial flora. Vitamin K derived from bacterial flora would be considered the most important source for ruminants since adequate vitamin K is available even when animals are fed vitamin K-free diets.

Vitamin K is present in fresh dark-green plants. It is abundant in pasture and green roughages, thus providing high quantities of vitamin K to grazing livestock. Swine, poultry and feedlot animals would, however, receive little vitamin K from diets based on grains and oilseed meals.

Green leaves are the richest natural sources of vitamin K1. Light is important for its formation, and parts of plants that do not normally form chlorophyll contain little vitamin K. However, natural loss of chlorophyll as the yellowing of leaves does not bring about a corresponding change in vitamin K. Alfalfa meal is a good plant source of vitamin K while liver and fish meal are good animal sources of the vitamin. All by-product feedstuffs of animal origin, including fish meal and fish liver oils, are much higher in vitamin K after they have undergone extensive bacterial putrefaction. Cereals and oil cakes contain only small amounts of vitamin K.

The menaquinones (vitamin K2) are produced by the bacterial flora in animals and are especially important in providing the vitamin K requirements of most mammals. However, the chick does not receive sufficient vitamin K from intestinal microbial synthesis (Scott et al., 1982). The type of diet, independent of vitamin K concentration, will influence total menaquinone synthesis. Rats fed a diet based on boiled white rice had less menaquinone production and more severe vitamin K deficiency than animals consuming diets based on autoclaved black-eyed beans (Mathers et al., 1990).

Vitamin K production in the rumen and subsequent passage along the small intestine, a region of active absorption, make vitamin K highly available to the host. In nonruminants, site of synthesis is the lower gut, an area of poor absorption, and thus availability to the host is limited unless the animal practices coprophagy, in which case the synthesized vitamin K is highly available.

Vitamin K1 is not utilized by the feed industry, due to cost and lack of a stabilized form. Instead, water-soluble (vitamin K3) salts are used to provide vitamin K activity in feeds. Because of poor stability, menadione is not used as the pure vitamin, but is produced as water-soluble salts (Table 1). Water-soluble derivatives of menadione, including menadione sodium bisulfite (MSB), are the principal forms of vitamin K included in commercial diets. The menadione concentration is 50% for MSB, 45.4% for MPB, and 33% for MSBC (Table 5-1) (Schneider, 1989).


The major clinical sign of vitamin K deficiency in all species is impairment of blood coagulation. Other clinical signs include low prothrombin levels, increased clotting time and hemorrhaging. In its most severe form, a lack of vitamin K will cause subcutaneous and internal hemorrhages, which can be fatal. Vitamin K deficiency can result from dietary deficiency, lack of microbial synthesis within the gut, inadequate intestinal absorption or inability of the liver to use the available vitamin K. Clinical signs of vitamin K deficiency are similar in all poultry species, with most research completed with newly hatched chicks and growing broilers. A deficiency of vitamin K causes a reduction in the prothrombin content of the blood and, in the chick, may reduce the quantity in the plasma to less than 2% of normal. Since the prothrombin content of the blood of normal, newly hatched chicks is only about 40% that of adult birds, very young chicks are readily affected by a deficiency of vitamin K. A carryover from the parent hen to the chick has been demonstrated (Almquist, 1971). Laying hens fed on a diet containing vitamin K1 or vitamin K3 at 10 to 100 mg per kg (4.5 to 45 mg per lb) produced vitamin K-rich eggs (Suzuki and Okamoto, 1997). Therefore, breeder hen diets should be supplemented with vitamin K to ensure good chick health. Laying hens fed a diet deficient in vitamin K produce eggs low in the vitamin, and when the eggs are incubated, the chicks produced have low reserves and a prolonged clotting time. Adverse effects on blood clotting are not apparent until after hatching, when hemorrhaging and mortality may occur should trauma be encountered. As a consequence, the chicks may bleed to death from an injury as slight as that caused by debeaking or wing banding (Illus. 5-2).

Illustration 5-2: Vitamin K Deficiency, Hemorrhaging

Note the generalized hemorrhage due to severe vitamin K deficiency in a young chick.

Courtesy of M.L. Scott, Cornell University

In very young chicks deficient in vitamin K, blood coagulation time begins to increase after five to 10 days of age, with clinical signs occurring most frequently in chicks two to three weeks after they begin consuming a vitamin K-deficient diet. Hemorrhages often occur in any part of the body, either spontaneously or as a result of an injury or bruise. Postmortem examination usually reveals accumulations of blood in various parts of the body; sometimes there are petechial hemorrhages in the liver and almost invariably there is erosion of the gizzard lining. Even though inadequate dietary vitamin K alters bone osteocalcin, signs associated with the skeletal system are not as apparent as blood clotting problems. Although blood clotting was impaired and there was a reduction in bone gamma-carboxyglutamic acid concentrations, vitamin K deficiency did not functionally impair skeletal metabolism of laying hens or their progeny (Lavelle et al., 1994). Vitamin K-dependent gamma-carboxylated proteins have been identified as ligands for a unique family of receptor tyrosine kinases with transforming ability. The involvement of vitamin K metabolism and function in two well-characterized birth defects, warfarin embryopathy and vitamin K epoxide reductase deficiency, suggests that developmental signals from vitamin K-dependent pathways may be required for normal embryogenesis (Saxena et al., 1997).

Borderline deficiencies of vitamin K often cause small hemorrhagic blemishes on the breast, legs and wings, in the abdominal cavity and on the surface of the intestine (Illus. 5-3). Chicks show an anemia that, in part, may be caused by loss of blood, but also by the development of a hypoplastic bone marrow (Illus. 5-4). Even a borderline deficiency of vitamin K is of economic importance in broiler production because the hemorrhagic areas that occur in the legs or throughout the body may result in a high percentage of condemnations during inspection at the processing plant (Scottet al., 1982). A condition manifested by numerous small hemorrhages scattered throughout all tissues has been reported frequently in the commercial broiler industry (Almquist, 1978).

Illustration 5-3: Vitamin K Deficiency, Hemorrhaging

Note the hemorrhagic blemishes in the muscle of a chicken fed a vitamin K deficient diet.

Courtesy of M.L. Scottm Cornell University

Illustration 5-4: Vitamin K Deficiency in Poultry

Anemic appearance of fowl resulting from experimental vitamin K deficiency.

A number of considerations influence the likelihood of a vitamin K deficiency in poultry, including dietary sources of the vitamin, level of vitamin K in the maternal diet, intestinal synthesis, coprophagy, presence of sulfa drugs and other non-nutrients in the diet, and disease conditions. Chicks suffering from coccidiosis, a disease that causes severe damage along the intestinal tract, may bleed excessively or fatally. When sulfaquinoxaline or certain other drugs are present in the feed or in the drinking water or when coccidiosis is being treated, supplementary vitamin K is needed at levels up to 10 times that needed in the absence of these drugs (Scott et al., 1982). Antimicrobial agents suppress intestinal bacteria that synthesize vitamin K and in their presence the bird may be entirely dependent on dietary vitamin K (NRC, 1994). Arsenilic acid increases the need for dietary vitamin K in both breeder and chick diets. In poultry, little intestinal synthesis occurs because of the short digestive tract. The young chicken’s large intestine or colon, a major area of bacterial activity, comprises less than 6% of the total length of the intestinal tract, while the figure for the adult of the same species is 7% (Griminger, 1984). In other domestic animals, the relative length varies from 13% for the dog to 28% for the rabbit. Also, poultry cannot utilize the vitamin K synthesized by intestinal flora because the synthesis is taking place too close to the distal end of the intestinal tract to permit significant absorption. Rapid rate of food passage through the digestive tract may also influence vitamin K synthesis in poultry. Passage time in pigs, for a specific portion of the diet, may occur about 15 hours after feeding, but most of a given meal will be retained in the tract appreciably longer. A comparable time period for chickens would be approximately three hours (Griminger, 1984).

Fortification Considerations

As long as natural dietary vitamin K sources (e.g., green leafy plants) are sufficiently high and bacterial synthesis in the intestinal tract remains functional, supplementary dietary vitamin K is not strictly necessary. However, good sources of vitamin K such as green leafy plants are not usually fed to poultry. An exception is alfalfa meal, which is sometimes included in small amounts in poultry diets. Therefore, a source of vitamin K needs to be added to the diets of poultry since they are not getting sufficient fresh greens or their dried equivalent and are not synthesizing sufficient amounts of this vitamin in their gastrointestinal tract. Scott et al.(1982) reported that natural ingredients used in poultry diets some years ago probably contained sufficient vitamin K while present diets do not. The common feedstuffs used in past years, such as high levels of alfalfa meal, high-fat soybean and other oilseed meals and fish meals with some putrefication supplied ample vitamin K. Recent trends toward (1) eliminating levels of alfalfa for production of higher energy, higher efficiency diets; (2) solvent extraction of soybean and other oilseed meals; (3) improved processing of fish meals, resulting in lower menaquinone levels because of less putrefaction; and (4) use of vitamin K-inhibiting drugs in feed and drinking water have had a combined effect that makes supplementation of most present day poultry feeds a necessity. Vitamin K antagonists will increase the vitamin K needs of livestock. In adjusting dietary vitamin K fortification levels, an appropriate margin of safety is needed to prevent deficiency and allow optimum performance in poultry. Vitamin K antagonists include the use of certain antibiotics and sulfa drugs. Sulfonamides and broad-spectrum antibiotic drugs can virtually sterilize the lumen of the intestine (McDowell, 2000). Mycotoxins, such as aflatoxin, are toxic substances produced by molds. Supplemental vitamin K may be helpful in correcting vitamin K deficiency in aflatoxicosis. Nelson and Norris (1961) showed that the inclusion of 0.1% sulfaquinoxaline increased the chick’s need for supplemental vitamin K by four to seven-fold. When intestinal microflora are altered, an excellent source of vitamin K is lost.

The level of supplemental vitamin K should be adequate to meet the requirements under the wide variety of stress conditions encountered in practical poultry production. Squibb (1964) obtained increased prothrombin times, indicating a higher vitamin K requirement in chicks, during the early stages of Newcastle disease. Studies have shown an interrelationship between the severity of coccidiosis and vitamin K requirement and indicated that as much as 8 mg of vitamin K per kg (3.6 mg per lb) of diet was needed at times for maximum growth and feed efficiency. Scott et al. (1982) concluded that coccidiosis possibly produces a triple stress on the vitamin K requirement by (1) reducing feed intake and thereby the supply of vitamin K, (2) injuring the intestinal tract and reducing absorption of the vitamin and (3) treating the disease with sulfaquinoxaline or other anticoccidials that cause an increased requirement for vitamin K. Recovery of poultry from coccidiosis has been enhanced by high dietary levels of supplemental vitamin K.

Inadequate vitamin K under practical circumstances is most likely to occur during the starting period, and supplementation of the feed at this time is advantageous (NRC, 1994). Starting feeds seldom contain forage meals, and a poorly developed intestinal microflora together with the use of antimicrobials further reduces access to the vitamin.

Fleming et al. (1998) suggest that supplementation with extra vitamin K may be beneficial to bone strength at different ages in laying hens. Increasing dietary vitamin K (menadione) from 2 to 12 mg per kg (0.9 to 5.5 mg per lb) increased cancellous bone volume in the proximal tarsometatarsus at 25 weeks. Studies are currently in progress to establish whether increasing the normal vitamin K supplement throughout the whole life of the hen has a beneficial effect on osteoporosis.

Vitamin K supplementation is needed if high dietary levels of other fat-soluble vitamins are fed (Abawi and Sullivan, 1989; Frank et al., 1997). Plasma clotting time is increased when vitamins A and E, in particular, are in excess.

Vitamin K1 is not currently available to the feed industry, as it is too expensive for this purpose; instead, water-soluble menadione (vitamin K3) salts are used to provide vitamin K activity in feeds. Because of instability, menadione is not used in feed as the pure vitamin but is formulated as an additional product with sodium bisulfite and derivatives thereof. Water-soluble derivatives of menadione include menadione sodium bisulfite (MSB), menadione sodium bisulfite complex (MSBC), and menadione dimethyl-pyrimidinol bisulfite (MPB) and the most recent compound introduced into the market, menadione nicotinamide bisulfite (MNB). The greatest menadione activity is 50% for MSB followed by 45.4% for MPB and 33% for MSBC (Schneider, 1986). Sometimes MSB is coated with gelatin to increase stability, resulting in a 25% menadione activity.

Stability of the naturally occurring sources of vitamin K is poor. However, stability of the water-soluble menadione salts is excellent in multivitamin premixes unless trace minerals are present (Frye, 1978). Basic pH conditions also accelerate the destruction of menadione salts; thus soluble or slightly soluble basic mineral substances should not be included in multivitamin premixes containing menadione. The MSB form is the most unstable formulation, followed by MSBC, MPB, and MSB-coated, and finally the most stable, MNB. A report by Huyghebaert (1991) determined the stability of different vitamin K formulations in a multivitamin, choline chloride and trace mineral premix at room temperature. At the end of four months, MSB retained 33%, MPB 57%, MSB-coated 62%, and MNB 83%.

Frye (1994) concludes that vitamin K in the form of MSB or MSBC is very sensitive to moisture and trace minerals, sensitive to light and gastric pH, and moderately sensitive to reduction and acid pH. Choline chloride is particularly destructive to vitamin K (Coelho, 1991). Less water-soluble forms or coated K3 is recommended in premixes that contain large quantities of choline chloride and certain trace minerals and especially in all cases where plain MSB is used or when premixes are exported or stored for an extended period of time (Schneider, 1986).

Vitamin Safety

Toxic effects of the vitamin K family are manifested mainly as hematologic 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 natural forms of vitamin K, phylloquinone and menaquinone, are nontoxic at very high dosage levels. The synthetic menadione compounds, however, have shown 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 as a pharmacologic treatment for a hemorrhagic condition. In studies with chicks, the major effect of toxic levels of menadione was hemolytic anemia, with a high mortality rate (NRC, 1987).

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