Reevaluation of Male Broiler Zinc Requirement by Dose-Response Trial Using Practical Diet with Added Exogenous Phytase

Abstract

Some reports indicate a wide range for Zn requireme nts for broiler chickens i.e. from 10.6 to 105 mg kg -1 . A number of factors other than dietary Zn concent ration determine the need for supplementation, principally dietary p hytate. 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. Experimenta l design was a completely randomized design in a 4×4 factorial arrangement. Factors incl uded 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 f unctions 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 weig ht by using practical high phytate diet, low availability source of Zn, and exogenous phytas e was lower than Ross 308 recommendation (60 vs 100 mg kg -1 ). Keywords: Broiler chickens, Phytase, Practical diet, Requirement, Zinc .