Niacin (also known as B₃) is one of those vitamins that is essential to almost everything your horse does.
It is involved in numerous oxidation-reduction cycles throughout the body. Additionally, one of the co-enzymes it creates is essential in DNA processing, cell differentiation, and calcium mobilization from cells.
B₃ is widely available in your horse's diet, but some forms of it are in what is called the bound form, which is unavailable to your horse. Cereal grains contain high levels of B₃, but up to 90% of it may be in the bound form. Therefore, grains are regarded as having little to no B₃ in context of the horse's diet.
Alfalfa has a high level, followed by soybean meal and timothy hay. There is no estimate of how much B₃ found in forages may be in the bound form, but approximately 40% found in oilseeds is in the bound form.
B₃ is also able to be produced by the microbials through fermentation in the cecum.
The horse can also synthesize B₃ from tryptophan in its liver tissues. When this process is used, it takes approximately 60 mg of tryptophan to create 1 mg of B₃.
There has been no reported toxicity in horses. However, high oral intakes in humans have caused itching, sensations of heat, nausea, vasodialtion (swelling of blood vessels), headaches, and vomiting.
Studies on rats have suggested that oral intake greater than 350 mg of nicotinic acid (one form of the vitamin) equivalents/kg BW may have toxic effects. It is thought that injectable levels may have a lower toxicity threshold.
There has been no reports of deficiency in horses. In other species, deficiency shows up as severe metabolic disorders. These disorders are usually noticed because they cause lesions on the skin and digestive system.
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