CHAPTER I: LITERATURE REVIEW - Repository.lib.ncsu.edu

peripheral nerve degeneration (Jortner et al., 1987). Niacin deficiency is predominantlyrelated to angular deviations of the hock joint (Summers et al., 1984).The bioavailability of biotin in wheat was equal or less than 12%, in contrast to almost100% in corn (Bryden et al., 2006). Similar results were reported by Baker et al. (1978) andFrigg (1976) in chick growth assays. Bryden et al. (2006) suggested that the low digestibilityof biotin might result from the bird‟s inability to liberate biotin from wheat in a form suitablefor absorption, because biotin digestibility was not associated with the biotin concentration orany other characteristics of the wheat grain. Biotin is involved in the formation of malonyl-CoA, which is essential for de novo fatty acid synthesis and elongation of long-chainpolyunsaturated fatty acids (Watkins, 1989). Thus, biotin can modulate prostaglandin E 2 andobtain the desired effect on bone development (Watkins, 2002; Farquharson, 2003). Watkinset al. (1988) reported that biotin-deficient chicks had lower prostaglandin precursors such asdihomo-γ-linolenate (20:3ω6), arachidonate (20:4ω6), and eicosapentaenoate (20:5ω3)compared to chicks that received an adequate biotin level (500μg/Kg). As a consequence,periosteal bone appositional and bone formation rates, and percentage new bone formationwere reduced in the tibiotarsus of biotin-deficient chicks. Marginal nutritional deficiencies ofbiotin in practical diets have been associated with foot pad lesions in broilers (Harms andSimpson, 1975) and turkeys (Mayne, 2005). On the other hand, supplementation of biotin atdoses of 200, 300, and 400 μg/Kg improved growth rate and increased bone mineral content(Quarantelli et al., 2006). Furthermore, biotin supplementation of breeder hens results in anincrease in biotin level in eggs and a decrease of foot pad dermatitis in the progeny (Harms etal., 1979). Therefore, deposition of biotin in the egg is important for embryo development(Kjaer et al., 2006) and broiler growth performance.Carotenoids. Wheat has fewer carotenoids than corn (Bird, 1997; Blair and Paulson,1997). In avian species, the primary carotenoids of economical and ecological interest are theoxygenated carotenoids, including lutein, and its isomers zeaxanthin and canthaxanthin(Goodwin, 1984). Carotenoids are considered the second level of antioxidant defense after17