The physical and chemical forms of various vitamin products currently used to fortify feeds are usually different from the forms found in feedstuffs (Desired Characteristics of Multivitamin Premix). Modification of these naturally occurring vitamin forms is required to improve their stability, compatibility, dispersion and handling characteristics for feed fortification.
In order to obtain sufficient stability and compatibility with other feed components and properties required for application, vitamin producers attempt to devise vitamin forms according to the following criteria (Schneider, 1986):
In view of the nutritional importance of vitamins A, D3 and E, many commercial vitamin producers have succeeded in enhancing stability of these vitamins in two ways: (a) by mechanical means of enveloping minute droplets of the vitamin or vitamins in a stable fat or gelatin, forming small beads and thus preventing most of the vitamin from coming into contact with oxygen until it is digested in the animal intestinal tract, and (b) through use of effective antioxidants that markedly prolong the induction period that precedes active vitamin oxidation. The “stabilized” beadlet containing an effective antioxidant will protect these vitamins for storage periods up to six months without much loss of vitamin potency (Hoffmann-La Roche, 1988). Instability of vitamin D3 in peroxidizing diets is often overlooked. Studies have shown that very high dietary levels of vitamin D3 are completely destroyed in diets containing high levels of peroxidizing PUFAs, and chicks fed such diets suffer severe rickets by three weeks of age (Scott, 1973). Rickets was prevented by a normal level of vitamin D3 when the diet was supplemented with the antioxidant ethoxyquin at a level of 57 mg per kg of diet (26 mg per lb).
Stress factors affecting vitamin stability during manufacture and storage of a custom premix may include heat, oxygen, moisture, oxidation, reduction, trace minerals and pH. Research tends to indicate that moisture is probably the most important factor in causing vitamin stability problems in feed (McGinnis, 1988). Some vitamins, such as riboflavin, niacin, biotin, pantothenic acid and choline, generally have excellent stability in custom premixes. Other vitamins, such as vitamin A acetate, vitamin D3 and vitamin E acetate, are available and added as stabilized forms in custom premixes. Vitamin K, unstabilized vitamin A, unstabilized vitamin D3, thiamin, folic acid, vitamin C, vitamin B6and vitamin B12 have poor stability in custom premixes under various stress conditions (Frye, 1978).
Most vitamins are supplemented in dry forms for feed supplementation. In addition, liquid forms of some vitamins have been developed for certain applications. When an animal’s feed intake is insufficient to provide adequate vitamin intake, but where there is good control over water consumption, special dry or liquid water-dispersible vitamins A, D3and E products and multivitamin stress packs are available to add to drinking water. These will disperse in cold water into a fine emulsion with desirable physical, taste and chemical stability characteristics for short term use. These vitamin forms are useful in drinking water for pets and other animals.
Because of the high variability and unknown bioavailability of vitamins in feedstuffs, feed manufacturers have come to rely to a large extent on commercially synthesized vitamins. In practice, feed manufacturers usually ignore to a certain degree the contribution of many vitamins in feedstuffs and provide complete vitamin supplementation. Bauernfeind (1969) summarized the advantages of synthetic vitamins in animal feeds as follows:
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