title: Pharmacological zinc levels reduce the phosphorus-releasing efficacy of phytase in young pigs and chickens.
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 micromol of iP per minute from sodium phytate at 37 degrees 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 x 5H2O) on phytase efficacy also were investigated in a 12-d chick trial. Dietary treatments were arranged according to a 2(3) 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.
authors.affiliation: Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
authors.forename: N R
authors.initials: NR
authors.lastname: Augspurger
authors.forename: J D
authors.initials: JD
authors.lastname: Spencer
authors.forename: D M
authors.initials: DM
authors.lastname: Webel
authors.forename: D H
authors.initials: DH
authors.lastname: Baker
mesh_terms: D010832:6-Phytase / Q000737:chemistry / Q000378:metabolism*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001682:Biological Availability; D001846:Bone Development / Q000187:drug effects; D001842:Bone and Bones / Q000378:metabolism; D002645:Chickens / Q000254:growth & development / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007408:Intestinal Absorption; D008297:Male; D010758:Phosphorus / Q000493:pharmacokinetics*; D011897:Random Allocation; D013552:Swine / Q000254:growth & development / Q000378:metabolism*; D015430:Weight Gain / Q000187:drug effects; D015032:Zinc / Q000494:pharmacology*
chemical_list: D010758:Phosphorus; D003300:Copper; D010832:6-Phytase; D015032:Zinc