Your Horse and B Vitamins

cellular energy cycle in horses. Thiamin is perhaps best known in the equine world as a calming nutrient and is often recommended for horses with anxiety or spookiness. Thiamin deficiency can lead to bradycardia slower than normal heart rate anorexia reduced appetite and ataxia instability caused by neurological dysfunction. Thiamin is the suggested treatment for horses that have consumed excessive amounts of the weeds marestail horseweed bracken fern or Queen Annes Lace and an excellent source of it is brewers yeast.
Vitamin B2 riboflavin is an important cofactor in energy metabolism. Deficiencies have never been proven in horses but in other species deficiency of it has been linked to poor hair coat dermatitis and eye problems. The best natural feed sources are green leafy forages like alfalfa and clover and to a lesser degree grass forages.
Vitamin B3 niacin is important for energy metabolism and is believed to be important for calcium metabolism as well. Horses can manufacture niacin in the liver but it is also supplied by the hindgut microbes. A deficiency has never been demonstrated in horses suggesting that a sufficient supply is provided through a combination of diet microbial growth and healthy liver function.
The role of biotin 
Vitamin B7 biotin is essential for cell proliferation and reproduction. Biotin is most often supplemented for improved hoof wall and hair coat quality and although NRC has not established a minimum biotin intake for horses it does recommend that horses get at least 10 to 30 mg per day of supplemental biotin. Virtually all of our favourite hoof supplements contain biotin but do make sure when reviewing tags that the product you buy provides at least 10 mg 10000 μg daily.
Also known as folate when in its naturally occurring form vitamin B9 folic acid is an important B vitamin. Folates role is prominent in the rapid cell growth of tissues or where rapid turnover of cells is needed. Folate deficiency has not been described in horses but research has shown that the need for this vitamin increases in horses engaged in intense exercise or in a state of lactation growth or gestation. Folate is provided either by the microbes in the hindgut or from fresh forage but as many of our horses do not get fresh forage in significant quantities supplementing this vitamin can be advisable.
Of particular concern are the very significant effects the drug treatments sulfadiazine and pyrimethamine have on folate
production in horses. These drugs are used in the treatment of equine protozoal myeloencephalitis EPM and they appear to affect the microbial synthesis of folate in horses. If treatments are short then the horse can recover the ability to produce this important vitamin but unfortunately treatment for EPM can be a lengthy process which can make this a cause for concern. Certainly this is something that should be discussed with your veterinarian if you do have a horse with EPM as it seems that simply supplementing your horse with synthetic folic acid is not helpful. In the case of pregnant mares treated for EPM use of these medications runs the risk of delivering foals with congenital defects.