All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy.  B vitamins, often referred to as B complex vitamins, also help the body use fats and protein. B complex vitamins are needed for healthy skin, hair, eyes, and liver and they also help the nervous system function properly.

Vitamins are a class of nutrients that are required in small amounts by the horse. Vitamins can be divided into two types; fat soluble and water soluble. B Vitamins are water soluble so therefore are not stored in the fat and can be more safely added to a horse’s diet without risk of toxicity.  Vitamins that are water soluble are excreted from the body on a daily basis in the urine.

There is no information on the quantitative requirements of the horse for many of the B vitamins and for several it is not even known whether or not they are dietary essentials.  An adequate amount of B vitamins are usually supplied for mature horses by providing quality forage in their diets either through grass or hay. 

How Can B Vitamin Synthesis Be Effected?

Horses that receive plenty of fiber in their diet create their own supply of B-vitamins, which are synthesized by the micro-organisms present in the hindgut. As long as there is plenty of fermentation of fiber in the intestinal tract, the supply of B-vitamins will be plentiful.

Since bacteria in the horse’s digestive tract produce B vitamins things that impact this can influence the B vitamin status of a horse.  Changes that affect the bacterial population may change the ability of the horse to synthesize of B vitamins and can reduce the availability of them.

Disruption to the fermentation of fiber in the hindgut can take place for a number of reasons, a low-fiber diet being a prime example. Other instances include any undue stress, such as when horses are traveling, through illness, rapid growth or following surgery or heavy antibiotic use.

Competition horses are often feed diets high in grain concentrates and low on fiber.  This ration combined with the stress of hard work make these horses prime candidates for vitamin-B supplementation.  Other horses that might need supplementation are older horses with poor teeth that cannot chew their fiber well.

Most horse owners understand that stress tends to decrease the horse’s ability to absorb B vitamins, but many do not know that drugs which selectively kill certain species of bacteria in the gut can affect absorption as well.  Parasitism can also reduce availability due to both the ulceration of the mucosa and due to competition for the vitamins.

There are also certain things that can affect particular B vitamins.  For example, moldy feed, especially hay contaminated by Streptomyces, makes Biotin unavailable for horses and the plants bracken fern, yellow star thistle or horsetail, interfere with thiamin utilization and transport.

Another way B vitamins can be compromised is if your horse suffers from chronic or clinical diseases that interfere with nutrient metabolism or has bouts of diarrhea.  Finally, its important to remember that along with electrolytes, B vitamins are also lost in sweat and therefore require replacement on a daily basis.

While there is much anecdotal evidence available about the effects of supplementing B-vitamins to horses, few actual research studies have been completed to determine the actual results of such supplementation.

The most researched and understood B vitamin in the equine diet is Biotin and, while there is not as much known about them, the other B vitamins of importance. examine niacin, riboflavin, thiamin, B₆ and B_12.