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Vitamin Supplements

Plants do not contain vitamin A. In plants, vitamin A activity is associated with carotenes. Beta-carotene is the carotene with the highest vitamin A activity. Chemically, beta-carotene is essentially two molecules of vitamin A.

Figure 10.7 illustrates the chemical structure of beta-carotene.

In the animal, beta-carotene is converted to vitamin A. Green plants are favorable sources of carotene; alfalfa-based products are fed as sources of carotene. Yellow corn also contains carotene. Vitamin A is produced in animal tissues. Vitamin A is concentrated in animal tissues such as the liver and kidneys. Fish liver oils are favorable sources of vitamin A. The primary forms of vitamin A are retinol, retinal, and retinoic acid.

Figure 10.8 illustrates the chemical structure of retinol.

Synthetic sources of vitamin A are also available. Retinol acetate, propionate, and palmitate are common synthetic sources. Vitamin A supplements may be added to a feed mixture or a liquid supplement and fed.

Figure 10.9 illustrates a vitamin A supplement.

Vitamin A is the vitamin most probable to present toxicity issues.

Carotenes and vitamin A are susceptible to oxidation. Vitamin A value may also be reduced as a result of processing and/or storage. Antioxidants are added to supplemental sources to minimize the loss of vitamin A. In general, vitamin A supplements are stable.

Vitamin A is expressed in International Units (abbreviated IU). One IU of vitamin A is equal to 0.344 micrograms retinyl acetate. One IU is also equal to 0.30 micrograms of retinol and 0.60 micrograms of beta-carotene. In general, vitamin A is added to animal rations.

Vitamin D is produced via the irradiation of sterols in the tissues of plants and animals. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are the primary chemical compounds with vitamin D activity. Ergocalciferol is the activated plant sterol. Cholecalciferol is the activated animal sterol. Four-legged animals (i.e. cattle, swine, horses, sheep, goats, etc.) are able to convert vitamin D2 to vitamin D3. In contrast, poultry are not able to efficiently convert vitamin D2 to vitamin D3. For all species, efficiency of utilization is greater for vitamin D3 as compared to vitamin D2. Vitamin D3 is the primary form of vitamin D in poultry rations. The metabolically active form of vitamin D is 1, 25 dihydroxycholecalciferol (1, 25-(OH)2-D3) or calcitriol. Calcitriol is synthesized with the addition of one hydroxyl group in the liver and one hydroxyl group in the kidney of the animal.

Figure 10.10 illustrates the chemical structure of calcitriol.

Sun-cured forages and fish oils are favorable sources of vitamin D. Plants only possess vitamin D activity following plant cell death. In addition, synthetic sources are produced from yeast, plant, or animal sterols irradiated with ultraviolet light. Irradiated animal sterols and fish products contain vitamin D3. Irradiated yeast and plant products contain vitamin D2.

In mixed feeds, vitamin D is relatively stable. Stability of the vitamin is influenced by other feedstuffs in the ration such as limestone and oxidizing compounds. Vitamin D requirement is influenced by the contents of calcium and phosphorus in the ration.

For poultry, vitamin D is standardized in International Chick Units. For other species, vitamin D is expressed in International Units of D3. One IU of vitamin D3 is equal to 0.025 micrograms of cholecalciferol. In general, vitamin D is added to animal rations.

Several chemical compounds possess vitamin E activity; the compounds are named tocopherols. Alpha-tocopherol is the compound with the highest vitamin E activity.
Figure 10.11 illustrates the chemical structure of alpha-tocopherol.

Germ oils in green plants are favorable sources of vitamin E. Synthetic sources of vitamin E are also available.

Figure 10.12 illustrates a vitamin E supplement.

Animal requirements of vitamin E are influenced by distress and reproduction. In addition, the presence of selenium in the ration influences the requirement for vitamin E. Vitamin E is susceptible to oxidation.

Vitamin E is expressed in International Units. One IU of vitamin E is equal to 0.67 micrograms of d-alpha-tocopherol. One IU of vitamin E is also equal to 1 milligram of dl-alpha-tocopherol acetate.

Vitamin K1, K2, and menadione are the primary chemical compounds with vitamin K activity.

Figure 10.13 illustrates the chemical structure of menadione.

Green plants are favorable sources of vitamin K. Additional feedstuffs with vitamin K are soybeans and various grains. Vitamin K2 is synthesized by microorganisms. Menadione is the primary synthetic source of vitamin K.

Ruminants consuming sweet clover or being treated with medication may require a supplemental source of vitamin K.

Menadione is the reference standard for measuring vitamin K activity. Vitamin K is expressed as milligrams.

Natural feedstuffs including animal- and fish-based products, green plants, fermentation products, yeast, milk-based products, oilseed meals, and some seed parts are favorable sources of water-soluble vitamins. In addition, the bran layers are fair to moderate sources of water-soluble vitamins. Cobalamine is the only water-soluble vitamin not present in plants. Yeast and animal- and fish-based products are favorable sources of cobalamine.

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