There has been a bit of discussion in the last couple of years about whether vitamin K should be added to horse feeds and if so, which form is the most effective in supporting bone development.

Vitamin K plays a complex role in the body. It is best known for its role in blood clotting, but it is also involved in many other functions including bone development.

There are many different forms of vitamin K including K1 (phylloquinone), K2 (menaquinone) and K3 (menadione). K1 comes predominantly from green plants, K2 is produced by bacteria and K3 is the synthetic form of vitamin K. These 3 primary forms of vitamin K are then converted in the body to several vitamin K homologs, with each homolog having a different role in the body. The homolog 'menaquinone-4' is the one that is recognised as being most important in bone formation.

It has been suggested that the synthetic form of Vitamin K (K3 or menadione) is unable to play an effective role in bone formation. However, a recent study published by Terachi et al (2011) in the Journal of Animal Science showed that horses supplemented with K3/menadione had the highest plasma menaquinone-4 concentrations compared to horses supplemented with phylloquinone or menadione-4.

The authors concluded that 'menadione is likely the best source of vitamin K for bone health in horses'.