Synthetic vitamins are widely used in premixes for swine diets. The commercially synthesized vitamins are modified from natural vitamin forms to improve their stability, compatibility, mixability, and handling characteristics for feed supplementation. The natural source of vitamin E, d-α-tocopheryl acetate or natural vitamin E, is the only non-synthetic vitamin often used in swine diets. A list of sources of vitamins and respective units of activity is presented in Table 1.
The form of vitamin products determines important characteristics of vitamin quality. Vitamin forms with good stability are usually able to maintain good vitamin bioavailability. Vitamin forms with high flowability, high uniformity in mix, low dusting, and low caking provide optimal handling and mixing characteristics. Altogether, these characteristics are important because vitamins are added in such small amounts to swine diets that the presence or absence of vitamins in individual rations markedly affect performance and health.