The Evaluation of Zinc Source and Dose in Broiler Diets Fed at Different Calcium and Phosphorus Levels in the Presence or Absence of Phytase

Phytate is a strong chelator of macro- and microminerals in the gastrointestinal tract. Under an environment in which phytate is rapidly hydrolyzed, the digestion and absorption of Ca, P, Zn and other cations from raw materials can be increased. This study investigated the performance, mineral excretion and bone mineralization of broilers fed diets formulated to optimize phytate hydrolysis and supplemented with Zn in the form of a Zn amino acid complex (Zn-AA) or as Zn sulfate (Zn-S). A total of 5040 day-old Ross 308 straight-run broiler chicks were allocated to 84 pens in a complete randomized block design, with 7 treatments and 12 replicates per treatment. Treatments 1 and 2 followed the breed recommendations (RECs) for Ca and P inclusion according to a three-phase feeding program and were supplemented with 90 ppm Zn as Zn-S, with (treatment 1) or without phytase (treatment 2), where treatment 1 is representative of a typical commercial-type diet. The remaining five treatments followed the University of Maryland (UMD) REC for Ca and P inclusion in a five-phase feeding program. The UMD diets were supplemented with either 90 ppm Zn-S (treatment 3) or graded levels of Zn-AA at 20, 40, 60, and 80 ppm (treatments 4–7). Phytase (2000 FTU/kg) was added to all diets except treatment 2. Data were analyzed in JMP 16.0 using one-way ANOVA regression analysis for Zn-AA treatments and Rao–Scott chi-square analysis for categorical data. Broilers fed 80 ppm Zn-AA resulted in heavier (p < 0.05) bodyweight (BW) on d 10, 16, 24, 30, and 37 when compared to all birds fed Zn-S at 90 ppm. On d 10, broilers fed 80 ppm Zn-AA had a higher (p < 0.05) tibia ash and tibia Zn content compared to those fed 90 ppm Zn-S (285.34 vs. 258.53 mg/tibia; and 12.00 vs. 10.62 mg Zn). Breast yield was also higher when comparing 80 ppm Zn-AA and 90 ppm Zn-S using the UMD REC (30.12 vs. 29.32%). Furthermore, broilers fed 40 ppm and above of organic Zn had less severe back scratches at term. It was therefore concluded that supplementation of Zn-AA following the UMD Ca and P REC resulted in increased growth performance and promoted higher breast yield of broilers whilst improving welfare.