Reevaluation of Male Broiler Zinc Requirement by Dose-Response Trial Using Practical Diet with Added Exogenous Phytase
M. Zaghari, M. Avazkhanllo, and M. Ganjkhanlou
Some reports indicate a wide range for Zn requirements for broiler chickens i.e. from 10.6 to 105 mg kg^-1. A number of factors other than dietary Zn concentration determine the need for supplementation, principally dietary phytate. Therefore, the objective of the present investigation was reevaluation of the zinc requirement for broiler, fed practical diet supplemented with phytase in a dose-response trial. A total of 768 male Ross 308 broiler chicks were used. Basal corn-soy diet deficient in Zn was supplemented with experimental diets for making 16 dietary treatments. Experimental design was a completely randomized design in a 4×4 factorial arrangement. Factors included four levels of dietary zinc (24, 54, 84 and 114 mg kg^-1) and phytase (0, 100, 200, 300 FTU kg^-1). Treatments were replicated four times and each had 12 birds. Linear and nonlinear functions were derived for graded levels of zinc and phytase. Results indicated that effect of dietary zinc on body weight at 42 days of age was significant (P< 0.01). The fitted quadratic model estimated 66.7, 64.8, and 60.1 mg kg^-1 zinc requirement for body weight at 28, 35, and 42 days of age, respectively (P< 0.001), while the fitted two slope broken line estimated 53.5, 53.8 and 57.4 mg kg^-1 zinc requirement for body weight at the same ages, respectively (P< 0.002). Zinc equivalence value of phytase was estimated to be 0.225 mg kg^-1 FTU^-1 and added phytase increased liver zinc storage too (P< 0.01). Estimated zinc requirement for body weight by using practical high phytate diet, low availability source of Zn, and exogenous phytase was lower than Ross 308 recommendation (60 vs 100 mg kg^-1).
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