There are two main classes of vitamins: fat-soluble and water-soluble.
The fat-soluble vitamins are A, D, E, and K, and they are listed on horse feed tags as IU/lb. This stands for “International Units per Pound”. They are able to be built up and stored in the body fat and other tissues, and thus are not absolutely required on a daily basis, but should be considered an important part of your horses’ regular nutritional program.
Water soluble vitamins, which are the b-vitamins such a niacin, thiamine, folic acid, biotin and many others, are excreted from the body on a daily basis in the urine. All of the B-complex vitamins are essential to horses, but they are synthesized by bacteria in the cecum and colon from ingested feed. After microbes form the vitamins, they are absorbed through the intestinal wall and are available for use by the horse’s body cells. Bacteria in healthy adult horses generally produce adequate levels of the B-complex vitamins.
While none of the vitamins are required by law to be listed on a feed tag, more and more feed companies ARE guaranteeing the levels included in the feeds. These are generally listed on the tag in either mg/kg or mg/lb, so it is important when comparing feeds or supplements to make sure you are comparing the same unit of measurement.
In coming blog posts, we will look at several of the vitamins individually to learn more about what they are each responsible for.