It is generally considered that phylloquinone in forage along with menaquinones synthesized by intestinal microbes meet the requirement of horses. We investigated the concentrations of fecal and plasma menaquinone-7 (MK-7) and the effect of MK-7 supplementation on plasma vitamin K concentration in adult horses.
Fecal and plasma samples were collected from twenty Thoroughbred horses aged 9.0±2.9 yr before MK-7 supplementation, and MK-7 concentrations in feces and plasma were determined. Subsequently the horses were allocated to 4 groups (n = 5) and each group was given MK-7 at 20 μmol/d, 40 μmol/d, 60 μmol/d, or no MK-7 supplement for 7 d. Plasma samples were collected before feeding, and 2, 4, and 8 h after feeding on d 7, and plasma concentrations of menaquinone-7 were determined (Experiment 2). Although fecal MK-7 concentration can be measured in all horses without supplying vitamin K, plasma MK-7 concentration was extremely low and was under the measurement limit in some horses. Additionally, the relationship between plasma concentration and fecal excretion of MK-7 was not observed. We suggest that MK-7 produced by intestinal bacteria is not important for horses. Plasma MK-7 concentration was higher in the 40 μmol/d group (P &;lt 0.001) and the 60 μmol/d group (P < 0.001) than in the control group through the experiment. Further, plasma MK-7 concentration was not changed after feeding in the 40 μmol/d group; plasma MK-7 concentration was stably high in this group. These results suggest that MK-7 is a good source of vitamin K for bone health in horses because the supplementation of MK-7 increases its plasma concentration greatly and continuously.
