Vitamin K requirements of ruminants are met by a combination of dietary intake and microbial biosynthesis in the rumen and intestines that may involve intestinal microorganisms such as Escherichia coli. Ruminal microorganisms in particular synthesize large amounts of vitamin K, which explains why ruminants do not appear to need a dietary source of the vitamin except during coumarin toxicity. The ruminant can absorb considerable amounts of ruminally synthesized vitamin K in the small intestine via active transport. In dairy calves fed milk replacer, there was no evidence of vitamin K deficiency based on prothrombin times, but the authors noted that supplementary vitamin K was observed to have health benefits in pre-ruminant calves, warranting further study (Nestor, Jr. and Conrad, 1990). Additionally liver, spleen and intestinal tissue levels of menaquinone-4 were increased significantly by feeding 8 or 16 mg MSBC per kg of diet dry matter (Nestor, Jr. and Conrad, 1990).
Due to rumen and intestinal microbial synthesis, quantifying a precise vitamin K requirement for ruminants is difficult. Rapid rate of passage (e.g., diarrhea) through the digestive tract may also influence vitamin K synthesis in cattle. The daily requirement of most species falls in a range of 2 to 200 µg vitamin K per kg (0.91 to 91 µg per lb) body weight. It should be remembered that this requirement can be altered by age, sex, stress, anti-vitamin K factors such as coumarin or T-2 toxin, disease conditions and any condition which impairs lipid absorption, alters intestinal flora or interferes with liver function.