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Vitamins

The sixth nutrient is vitamins. Vitamins are chemically unrelated, organic compounds.

Vitamins are divided into two categories. Vitamins are either classified as water soluble or fat soluble. Table 2.4 lists the twelve water soluble vitamins.

Collectively, the water soluble vitamins, except ascorbic acid or vitamin C, are often referred to as the B-complex vitamins. The functions of a number of the water soluble vitamins are to act as enzyme cofactors. In the case of vitamins, cofactors are organic molecules required for the activation of enzymes. Table 2.5 lists the four fat soluble vitamins and each of the vitamin’s primary functions.

Similar to the other nutrients, the primary site of absorption is the small intestine. Site of production will influence utilization efficiency for water and fat soluble vitamins. Absorption efficiency for fat soluble vitamins is also directly related to the presence of dietary fat and bile.

There are three sources of vitamins. The first source is the animal tissues. Some species are able to synthesize required amounts of some vitamins within their tissues. The second source is the microorganisms within the GI tract. For ruminants and horses, the microbes synthesize at least the required amount of most of the water soluble vitamins. Therefore, with the exception of high producing animals, ruminants and horses do not have a dietary requirement for the water soluble vitamins. In addition to the water soluble vitamins, rumen microbes also synthesize adequate amounts of vitamin K. Microorganisms present in the GI tract of other species, such as the monogastrics, also produce vitamins. However, as production is posterior to the small intestine, utilization efficiency varies by species and by vitamin. The final source of vitamins is the diet. Dietary vitamins supplement the vitamins synthesized within the tissues and by the microorganisms of the GI tract to fulfill the requirement. Dietary vitamins are often consumed in inactive states and subsequently converted to active states within the body.

Vitamin solubility influences the required frequency of dietary supplementation and the potential for deficiencies and toxicities. As excess water soluble vitamins are not stored in the tissues, daily dietary supplementation is necessary for all required water soluble vitamins with the exception of cyanocobalamin. In contrast, fat soluble vitamins are stored in tissues such as the liver and adipose tissue. Therefore, daily supplementation is not required. It is important to monitor for deficiencies of both water and fat soluble vitamins. Although required in small amounts, exclusion of one required vitamin will result in deficiency symptoms and eventually death. As excess water soluble vitamins are eliminated from the body, generally, water soluble vitamins do not cause toxicity. In contrast, short or long term excess of fat soluble vitamins can cause toxicity.

Individual vitamins are required in small amounts. Similar to the other nutrients, vitamin requirements will vary between and within species. In general, monogastrics require a majority of the water soluble and fat soluble vitamins and herbivorous monogastrics and ruminants require the majority of fat soluble vitamins. The following are general recommendations by species. Poultry require dietary sources of all vitamins except ascorbic acid, inositol, and PABA. The dietary vitamins required for swine include riboflavin, niacin, pantothenic acid, Cyanocobalamin, and vitamins A, D, and E. Horses require fat soluble vitamins A, D, and E. And dietary vitamins required for ruminants include A and possibly vitamins E and/or D.

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