Vitamins are classified into two groups: Soluble & Insoluble. This is determined by their solubility in either water or fat. The solubility factor determines the location within the horses system each vitamin functions.

All vitamins are required in very small amounts.

Importance

Horses cannot synthesise vitamins of their own accord within the system and require vitamins to be supplied in feed or supplementation. The vitamin content and individual vitamin levels can vary in respect to whether horses feed in the field is green or dry, the season and at what stage of maturation the growth is at.

Vitamins are essential in the horses system for numerous reasons. In respect to the broad picture vitamins are required for:

• Metabolism
• Bone growth and development
• Reproduction
• Respiration
• Vision
• Skin and coat health
• Liver and kidney function
• Immune system
• Growth
• Performance

Vitamins are stored within the liver alongside other nutrients as well as the blood stream but levels need to be restored on a regular basis if the desired levels are to be maintained.

Monogastric animals such as horses require vitamin B12 with little evidence for the benefit of cobalt. Ruminants (cattle) require cobalt in order to synthesise vitamin B12.

Deficiency

If a deficiency of a vitamin or several vitamins occurs, this can result in health and performance issues surrounding the areas mentioned in the points above.
Exact levels of each vitamin required in a horses diet depends again on the age, workload etc of each individual horse.