ISSUE FOCUS FEED & ADDITIVE MAGAZINE July 2022 45 Vitamin E is a biological antioxidant and a free radical scavenger that protects the cells and lipid rich-membranes from oxidative damage and is considered as the core of the antioxidant system. Among the four tocopherols and four tocotrienols (designated as α-, β-, γ-, and δ-), only the α-tocopherol form has the biological activity to meet the animal's Vit E requirements. Dietary supplementation of various levels of Vit E can improve broiler performance and reduce the oxidative stress experienced under high environmental temperatures. Several studies have shown a positive effect of n-3 on bone mineral density (BMD) and bone mineral content (BMC) in animals. Zinc is used in poultry diets because of its antistress effects. Moreover, its requirement increases and its retention decreases during stress. Zinc deficiency also causes shortness and thickness in long bones of legs and wings. There is also some evidence suggesting supplemental Zinc can alleviate negative effects of heat stress in broiler chickens. Bone breaking strength is measured by evaluating the reaction of the bone to stress and force. An increase in bone mineralization is accompanied by an increase in bone stress and bending moment values. Bone mechanical strength is affected by nutrition, genes, age, sex, environment and etc., for the expression of collagen and proteins, quantity and quality of the organic and inorganic material, content and size of the mineral material, and design and structure of the bone (Boskey et al., 1999). Velleman (2000) explained the structural complexity and composition of bone associated with strength, which varied according to the age and nutritional status of the bird: femur compression strength = 11.9 + 0.0141 (bird BW). However, contradictory data regarding the effect of vitamin E on collagen synthesis exists, and few studies have reported its influence on cartilage development. In fact, increasing in thickness of the growth plate was proportional to DL-α-tocopheryl acetate dose. The effect of vitamin E on chondrocytes was observed by Xu et al. (1995) in chicks fed by two levels of DL-α-tocopheryl acetate and two dietary lipids. The thickness of the entire growth plate cartilage and of the lower hypertrophic chondrocyte (mineralized) zone was significantly wider in animals fed the greater level of vitamin E. α-tocopherol protects PUFA from lipid oxidation. However, the effect of α-tocopherol and zinc supplementation on bone strengthen in poultry has rarely been studied and is rather controversial. The relation between dietary fat, zinc and vitamin E with heat stress on femur breaking strength has been studied separately. EFFECTS OF DIETARY FAT, VITAMIN E, AND ZINC SUPPLEMENTATION ON TIBIA BREAKING STRENGTH Performance High environmental temperature reduced the feed intake, body weight and increased feed to gain ratio in broiler. The diets contain saturated fat have been a significant effect on feed intake and body weight although the same result on feed to gain was not convenient. Addition of zinc and vitamin E to the unsaturated oil ration have been increased in body weight of broilers though it was less than body weight of tallow ration.
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