Vitamin K

When a fat-free, low-cholesterol diet is fed to chicks, they develop a hemorrhagic condition that is cured by the addition of alfalfa meal.[9] It was demonstrated that the lipid-soluble portion of green plants and bacteria had the capacity to restore blood clotting time to normal. Although the chemical forms in green plants (Ki) and bacteria (K2) differ, the similar quinone compounds were collectively called vitamin K. Although other commercial water-soluble forms are available, menadione bisulfite is the form most commonly added to poultry and swine diets.[5,10]

Absorption of plant and bacterial quinone compounds are dependent upon the fat digestive process, whereupon the vitamin is absorbed and transported in the lymph. Bacterial products can supply vitamin K to nonruminants practicing coprophagy, but dietary antibiotics may alter intestinal microbial synthesis of the vitamin.[10] Plants and rumen bacteria are major suppliers for ruminants on pasture, with deficiencies being rare. The consumption of moldy sweet clover hay produces a fungal metabolite (dicoumarol) that inhibits the synthesis of blood clotting factors.[4'11] All forms of vitamin K are located in the liver.[8'9]

Vitamin K modifies several liver proteins, largely involving the blood clotting factors, but its effects are posttranslational.[9] Vitamin K serves to activate the proteins, specifically at the g-carboxyglutamate site, to increase the binding affinity of Ca ions for the clotting of blood.[9] Similar mechanisms may occur in other tissue and it probably has a role in bone mineralization.

Deficiency symptoms of vitamin K include prolonged bleeding, poor clotting, hematoma in tissue, and death from uncontrolled hemorrhages. Animal lameness, stiffness, and blood in the urine are related to the deficiency. Dicoumarol can pass the maternal fetal barrier and the developing fetus can be affected. Because blood clotting is affected by vitamin K, the prothrombin clotting time is a rapid and useful clinical tool in detecting the deficiency.[9]

Excess vitamin K does not seem to affect any major animal species. The newer water-soluble forms may react with free tissue sulfhydryl groups and cause hemolytic anemia in liver tissue, and brain damage.

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