Growth performance and bone zinc concentration in broiler chickens with dietary supplementation of organic zinc.

Abstract

The objective was to determine the optimal dietary organic zinc (Zn) concentration to maximize growth performance and skeletal Zn deposition in broilers. A total of 240 one-d-old broiler chicks were assigned to 5 dietary treatments for a 20-d feeding trial, with 8 cages per treatment. All diets met or exceeded recommended nutrient requirement estimates for broilers, except for Zn. The 5 treatments were as follows: (1) a corn-soybean meal-based diet with 40 mg/kg inorganic Zn from ZnSO4·7H2O; (2) a corn-soybean meal-based diet without supplemental Zn; (3-5) treatment 2 supplemented with 5, 10, or 20 mg/kg of organic Zn from Zn proteinate. Body weight gain, feed intake, and feed conversion ratio were measured from d 0 to 20. On d 20, tibia samples were collected, and Zn concentration in tibia ash was determined. Orthogonal polynomial contrasts were used to evaluate linear and quadratic responses to increasing supplemental organic Zn. Pairwise contrasts were performed between diets containing 40 mg/kg of inorganic Zn and those containing either 10 or 20 mg/kg of organic Zn. The optimal supplemental level of organic Zn for tibia Zn concentration was estimated using a one-slope broken- line model. Average daily gain, feed intake, and tibia Zn concentration increased linearly (p<0.05) with increasing organic Zn. Broilers fed 10 mg/kg organic Zn exhibited similar growth to those receiving 40 mg/kg inorganic Zn, but lower tibia Zn concentration (p<0.001). In contrast, 20 mg/kg organic Zn supported both growth and bone Zn deposition equivalent to the inorganic Zn group. A one-slope broken-line analysis indicated that 16.5 mg/kg organic Zn was the minimum level required to maximize tibia Zn concentration. Bioplex Zn was more bioavailable than inorganic Zn from Zn sulfate, and 16.5 mg/kg was sufficient to optimize both growth and skeletal Zn deposition in broilers.