What it is
Vitamin K3 (menadione) is a synthetic form of vitamin K. Its feed additive forms are menadione sodium bisulphite and menadione nicotinamide bisulphite, and 1 mg of vitamin K3 is counted as 1 mg of menadione [1].
Do horses need it?
Vitamin K requirements are not established in horses: microbes in the caecum and colon make enough, with some from plant vitamin K (phylloquinone) in the diet [2]. Mouldy sweet clover hay can cause vitamin K–dependent clotting problems [2].
Safety
Injected menadione is toxic to the kidneys in dehydrated horses [2]. EFSA found no new evidence to change its conclusion that vitamin K3 is safe for target animals under its authorised conditions of use in feed [1].
See also reading feed labels.
Sources
- 1. EFSA FEEDAP Panel (Villa RE, Azimonti G, Bonos E, et al.). Assessment of the feed additives menadione sodium bisulphite (3a710) and menadione nicotinamide bisulphite (3a711) (vitamin K3) for all animal species for the renewal of their authorisation. EFSA Journal 2025;23(12):e9792. doi:10.2903/j.efsa.2025.9792 https://pmc.ncbi.nlm.nih.gov/articles/PMC12699196/ (accessed 2026-11-07)
- 2. Liburt NR (peer reviewed by Boyle AG). Nutritional Requirements of Horses and Other Equids. MSD Veterinary Manual, Professional Version. Merck & Co., Inc., Rahway, NJ. Last full review February 2026. https://www.msdvetmanual.com/management-and-nutrition/nutrition-horses/nutritional-requirements-of-horses (accessed 2026-11-07)
Last edited 7 Nov 2026, 1:48 am