Vitamin E is an essential nutrient for humans and the vast majority of animals. Recently, the benefits of supplementing human and animal diets with vitamin E has been greatly emphasized due to its critical role in many biological functions. Vitamin E provides the first line of defense in protecting the integrity of body organs, tissues, and cell membranes from damage caused by biological oxidation. In this function, vitamin E acts as an internal antioxidant to prevent highly unstable free radicals, referred to as peroxides, from attacking the polyunsaturated fatty acids of cell membranes. Vitamin E is also crucial for:

• Tissue respiration

• Energy metabolism

• Immune system function

• Hormone synthesis

• Thyroid function

• Extended shelf life of meat

• Synthesis of critical body components

Vitamin E is the generic name for a group of lipid-soluble compounds known as tocopherols and tocotrienols (tocols). Each of these compounds has four different "formulas":

• Alpha

• Beta

• Gamma

• Delta

These "formulas" act as biological vitamin E antioxidants to varying degrees, the most powerful being alpha-tocopherol. The number of methyl groups on the chromanol ring determines the efficiency at which a "formula" will act as an antioxidant. The relative biopotency of the four "formulas" are alpha 100%, beta 25-40%, gamma 1-11%, and delta 1%.

The vitamin E requirement is dictated largely by the level of biological oxidation the animal or human encounters. Intensive animal production and dramatic improvements in growth rate and metabolic efficiencies have increased the need for higher dietary levels of vitamin E. Environmental and disease stresses also contribute to increased oxidation; thus, increasing vitamin E need.

The commonly available source of stable vitamin E used in animal feed is synthetic dl-alpha-tocopheryl acetate, which exists in equal amounts of eight isomers (see Table 1). An alternative natural form of stable vitamin E is d-alpha-tocopheryl acetate, which is derived from vegetable oils and exists in the form of one isomer (see Table 1). The relative biopotency of the eight different isomers of vitamin E is shown in Table 1.

Standard biopotency values have been established to differentiate the sources of vitamin E (see Table 2). Biopotency refers to the amount of a nutrient associated with some measured physiological endpoint, such as growth or prevention of a specific deficiency symptom. The biopotency values are expressed as international unit (IU) per unit of weight (mg).

Since the establishment of these values, there have been additional studies conducted to determine the biopotency of vitamin E compounds. The relative biopotency of dl-alpha and d-alpha tocopheryl acetates covers a wide range of values according to species, stage of production, degree of tissue depletion, dietary concentration, and measured response. The reported values have ranged from 1.2 to 3 times greater biopotency for d-alpha-tocopheryl acetate (natural vitamin E source) compared to dl-alpha-tocopheryl acetate (synthetic vitamin E source).

Based on uptake and retention, body tissue data indicates a preference for d-alpha-tocopherol. The data in Table 3 shows the difference in relative concentration and retention of vitamin E in body tissues when comparing the natural (d) and synthetic (dl) forms. Metabolic differences have been shown in a human study. Volunteers consuming 150 mg of deuterium-labeled d-alpha or dl-alpha excreted 2.7 times more dl-alpha than d-alpha. This demonstrated a preference to more rapidly metabolize and excrete the dl-alpha form.

Based on recent animal studies, d-alpha-tocopheryl acetate (natural) may be a better alternative to increase tissue levels and retention of vitamin E compared to dl-alpha-tocopheryl acetate (synthetic).

TABLE 2
Common Sources of Vitamin E	Biopotency (IU/mg)
dl-alpha-tocopheryl acetate	1.0
d-alpha-tocopheryl acetate	1.36
dl-alpha-tocopherol	1.1
d-alpha-tocopherol	1.49
dl-alpha-tocopheryl acid succinate	0.89
d-alpha-tocopheryl acid succinate	1.21

 

TABLE 3
Tissue	Relative Concentration of d-alpha Versus dl-alpha	Times of Retention of d-alpha Versus dl-alpha
Brain	5.3	3.2
Red blood cells	3.6-4.0	-
Plasma	2.6-4.0	-
Heart	1.9	2.6-3.2
Muscle	1.7	2.6
Liver	--	1.2-2.3
Lung	--	1.9

For More Information e-mail at AN_EquineHelp@admworld.com

or call toll free
EQUINE NUTRITION HELPLINE
1-800-680-8254
7:30 AM to 4:30 PM Central Time

ADM Alliance Nutrition, Inc. 1000 North 30th Street P.O. Box C1 Quincy, IL USA 62305-3155