Pharmacological zinc levels reduce the phosphorus-releasing efficacy of phytase in young pigs and chickens

A pig trial and a chick trial were done to determine the effect of high levels of Zn and Cu on the P-releasing efficacy ofphytase. Ninety-nine individually fed pigs (7.2 kg) were given ad libitum access to one of 11 experimental diets for a period of 21 d. Fibula ash (mg) was regressed against supplemental inorganic P (iP) intake (g) to establish the standard curve, from which phytase treatments were compared to determine P-releasing efficacy. The basal diet was a corn-soybean meal diet with no supplemental P (21% CP, 0.075% estimated available P, 130 mg of Zn/kg, as-fed basis). Diets included three graded levels of supplemental iP (0, 0.075, 0.150%) from reagent-grade KH 2 PO 4 , two levels of phytase (500 and 1,000 FTU/kg) from EcoPhos, 1,500 mg of Zn/kg from either Waelz ZnO or basic Zn chloride (Zn 5 Cl 2 (OH) 8 ), and all combinations of phytase and Zn. One phytase unit (FTU) was defined as the amount of enzyme required to release 1 μmol of iP per minute from sodium phytate at 37°C and pH 5.5. Phytase supplementation improved (P 0.50) on growth performance, but decreased (P 0.30) the response to phytase. These results suggest that pharmacological levels of Zn chelate the phytate complex, thereby decreasing its availability for hydrolysis by phytase.