Effects of 25‐hydroxycholecalciferol with two D3 vitamin levels on production and immunity parameters in broiler chickens

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Scientific studies have revealed a close relationship between vitamins and immunity (Chou, Chung, & Yu, 2009; Kidd, 2004). The inclusion of vitamin D3 in poultry diets is necessary for the absorption, transport and utilization of calcium and phosphorus. Other studies have demonstrated the important role of vitamin D3 in the development of skin cells and blood cells and in the control of immune cell activity (Bunce, Brown, & Hewison, 1997; Capiati, Benassati, & Boland, 2002; Lymboussaki et al., 2009). The hydroxylation of vitamin D3 to (25(OH)D3) and, subsequently, to 1,25(OH)2D3 is required for vitamin D3 to perform its function in the body. Hence, this research was initiated to study the potential benefits of adding various vitamin D3 metabolites to poultry diets. 1,25‐(OH)2D3 is the active form of vitamin D3 (DeLuca & Zierold, 1998) and has been shown to augment the activity of leucocytes and macrophages (Capiati et al., 2002; Lymboussaki et al., 2009).
The current National Research Council (NRC)‐recommended (1994) level of vitamin D3 supplementation is 200 IU/kg; however, this value is intended only to avoid vitamin deficiency and is much lower than the level used to increase production (5,000 IU/kg) in the poultry industry. Using 25(OH)D3 is associated with a number of advantages compared using to vitamin D3 and its other metabolites. For example, 25(OH)D3 exhibits better intestinal absorption because its polar nature allows absorption to occur by passive diffusion; in contrast, the absorption of vitamin D3 requires micelle formation (Calabotta, 1997). Furthermore, once it is in the bloodstream, 25(OH)D3 has a higher affinity for its carrier protein and a longer half‐life. Thus, the serum level of 25(OH)D3 is an excellent indicator of vitamin D3 status or availability (Soares, Kerr, & Gray, 1995). Given these factors, the present study seeks to evaluate the effects of dietary 25(OH)D3 supplementation on the growth and immunity of broilers.
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