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Pharmacological zinc levels reduce the phosphorus-releasing efficacy of phytase in young pigs and chickens^1,2

N. R. Augspurger^*,3, J. D. Spencer, D. M. Webel and D. H. Baker^*,4

^* Department of Animal Sciences, University of Illinois, Urbana 61801 and and United Feeds, Inc., Sheridan, IN 46069

⁴ Correspondence: 290 Animal Sciences Laboratory, 1207 W. Gregory Dr. (phone: 217-333-0243; fax: 217-333-7861; e-mail: dhbaker{at}uiuc.edu).

Abstract

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 of phytase. 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 KH₂PO₄, 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 (Zn₅Cl₂(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 < 0.01) weight gain, G:F, and fibula ash (% and mg). Bone ash (mg) was highest (P < 0.01) for pigs fed diets containing 1,000 FTU/kg of phytase. Supplemental Zn had no effect (P > 0.50) on growth performance, but decreased (P < 0.05) fibula ash (mg). Comparison of the phytase treatments to the standard curve (r² = 0.87) revealed P-release values of 0.130 and 0.195% for 500 and 1,000 FTU of phytase/kg, respectively, in the absence of Zn, whereas in the presence of Zn (pooled), P-release values were decreased (P < 0.01) to 0.092 and 0.132%, respectively. The effects of high levels of supplemental Zn (basic Zn chloride) and Cu (CuSO₄•5H₂O) on phytase efficacy also were investigated in a 12-d chick trial. Dietary treatments were arranged according to a 2³ factorial, with two levels each of supplemental phytase (0 and 500 FTU/kg from EcoPhos), Zn (0 and 800 mg/kg), and Cu (0 and 200 mg/kg). There was a phytase x Zn interaction (P < 0.01) for tibia ash. Thus, Zn supplementation decreased tibia ash in the presence, but not in the absence, of phytase. Supplemental Cu did not affect (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.

Key Words: Chicks • Copper • Phytase • Pigs • Zinc

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				N. R. Augspurger, D. M. Webel, and D. H. Baker An Escherichia coli phytase expressed in yeast effectively replaces inorganic phosphorus for finishing pigs and laying hens J Anim Sci, May 1, 2007; 85(5): 1192 - 1198. [Abstract] [Full Text] [PDF]

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