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Effects of supplemental dietary phytase and pharmacological concentrations of zinc on growth performance and tissue zinc concentrations of weanling pigs^1,2

Department of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803

	Abstract

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Three experiments were conducted to determine the effects of phytase, excess Zn, or their combination in diets for nursery pigs. In all experiments, treatments were replicated with five to seven pens of six to seven pigs per pen, dietary Ca and available P (aP) levels were decreased by 0.1% when phytase was added to the diets, excess Zn was added as ZnO, a basal level of 127 mg/kg of Zn (Zn sulfate) was present in all diets, and the experimental periods were 19 to 21 d. In Exp. 1, pigs (5.7 kg and 18 d of age) were fed two levels of phytase (0 or 500 phytase units/kg) and three levels of excess Zn (0, 1,000, or 2,000 ppm) in a 2 x 3 factorial arrangement. Added Zn linearly increased ADG and ADFI during Phase 1 (P = 0.01 to 0.06), Phase 2 (P = 0.02 to 0.09), and overall (P = 0.01 to 0.02). Gain:feed was linearly increased by Zn during Phase 1 (P = 0.01) but not at other times. Dietary phytase decreased ADG in pigs fed 1,000 or 2,000 ppm Zn during Phase 2 (Zn linear x phytase interaction; P = 0.10), did not affect (P = 0.27 to 0.62) ADFI during any period, and decreased G:F during Phase 2 (P = 0.01) and for the overall (P = 0.07) period. Plasma Zn was increased by supplemental Zn (Zn quadratic, P = 0.01) but not affected (P = 0.70) by phytase addition. In Exp. 2, pigs (5.2 kg and 18 d of age) were fed two levels of phytase (0 or 500 phytase units/kg) and two levels of Zn (0 or 2,000 ppm) in a 2 x 2 factorial arrangement. Supplemental Zn increased ADG and G:F during Phase 2 (P = 0.02 to 0.09) and overall (P = 0.07 to 0.08), but it had no effect (P = 0.11 to 0.89) on ADG during Phase 1 or ADFI during any period. Phytase supplementation increased ADG (P = 0.06) and G:F (P = 0.01) during Phase 2. Gain:feed was greatest for pigs fed 2,000 ppm Zn and phytase (Zn x phytase interaction; P = 0.01). Bone (d 20) and plasma Zn (d 7 and 20) were increased (P = 0.01) by added Zn but not affected (P = 0.51 to 0.90) by phytase. In Exp. 3, pigs (5.7 kg and 19 d of age) were fed a basal diet or the basal diet with Ca and aP levels decreased by 0.10% and these two diets with or without 500 phytase units/kg. Supplemental phytase had no effect (P = 0.21 to 0.81) on growth performance. Reduction of dietary Ca and aP decreased (P = 0.02 to 0.08) ADG, ADFI, and G:F for the overall data. These results indicate that excess dietary supplemental Zn increases ADG and plasma and bone Zn concentrations. Dietary phytase did not affect plasma or bone Zn concentrations.

Key Words: Bioavailability • Nursery pigs • Phytase • Zinc Oxide

	Introduction

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Pharmacological levels of Zn for weanling pigs have increased growth performance (Hahn and Baker, 1993; Carlson et al., 1999; Hill et al., 2000). Extensive feeding of high concentrations of Zn (up to 3,000 ppm) leads to the excretion of excess Zn in the manure, which could be an environmental concern (Case and Carlson, 2002).

Phytate P, which is poorly utilized by nonruminants, accounts for approximately two-thirds of the P content in cereal grains (Ravindran et al., 1995). Phytase is an enzyme that catalyzes the hydrolysis of P from the phytate molecule (Ravindran et al., 1995). Supplementation of phytase has improved the availability of phytate-bound P, decreased P excretion, and improved growth performance in both pigs (Yi et al., 1996b; Murry et al., 1997) and poultry (Simons et al., 1990; Sebastian et al., 1996; Johnston and Southern, 2000). Phytic acid is a strong acid, and it has the potential to form insoluble salts with cations such as Ca, Zn, Mn, Fe, Co, and Cu (Vohra et al., 1965), thereby decreasing the availability of these minerals. Phytate has the highest binding affinity for Cu and Zn (Maddaiah et al., 1964; Champagne and Hinojosa, 1987).

A negative effect of phytate on Zn availability was first demonstrated in chicks by O’Dell and Savage (1960). Lönnerdal et al. (1988) reported that phytate removal from soy formula enhanced Zn absorption and bioavailability in suckling rats. Supplementation of diets with microbial phytase improves the bioavailability and/or retention of Zn in both pigs (Lei et al., 1993; Adeola et al., 1995) and poultry (Yi et al., 1996a; Zanini and Sazzad, 1999). Therefore, the objective of our research was to determine the effects of phytase and the potential interactive effects of phytase and pharmacological levels of Zn on growth performance and tissue concentrations of Zn in weanling pigs.

	Materials and Methods

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General
All methodology related to animal care was approved by the Louisiana State University Animal Care and Use Committee.

Three experiments were conducted to evaluate the interactive effects of phytase, pharmacological concentrations of dietary Zn, as ZnO, and dietary Ca and P levels in diets for weanling pigs. Purebred Yorkshire and crossbred (Yorkshire x Landrace or Yorkshire x Landrace x Duroc) pigs from the Louisiana State University Agricultural Center Swine Unit were used in these experiments. All pigs were weighed at weaning and allotted to treatments on the basis of BW and ancestry, with gender equalized across treatments in randomized complete block designs. Pigs were housed in an environmentally controlled modular building in 0.97-m x 1.47-m pens on hard plastic slotted floors with an under-floor flush system. Feed and water were provided on an ad libitum basis throughout the experiments. Pigs and feeders were checked twice daily and were weighed at the end of each growth phase for calculation of ADG, ADFI, and G:F.

Treatments in Exp. 1, 2, and 3 were replicated with five, six, or seven pens, with seven, six, or six pigs per pen, respectively. In Exp. 1, 2, and 3, average initial and final BW were 5.7 and 10.3; 5.2 and 10.4; and 5.7 and 11.4 kg, and pigs were weaned at 18, 18, and 19 d of age, respectively. Phase 1 diets were fed for 7 d in all experiments, and Phase 2 diets were fed for 12, 13, or 14 d in Exp. 1, 2, and 3, respectively.

Diets were formulated (as-fed basis for all nutrients, Table 1) to provide 1.6 and 1.4% total lysine in Phases 1 and 2, respectively. The basal diet provided 127 ppm of Zn, and the diets were adequate in all nutrients for weanling pigs (NRC, 1998). The basal diet with no added phytase was formulated to provide 0.90% Ca and 0.55% available P (aP) for Phase 1, and 0.80% Ca and 0.40% aP in Phase 2. In the diets with added phytase, Ca and aP were decreased by 0.1%. Sand was used to replace ZnO and the monocalcium phosphate and limestone that was reduced by the addition of phytase, and rice hulls were used to replace phytase. Microbial phytase (Natuphos 600; BASF Corp., Mount Olive, NJ) was added at 0.083% of the diet to provide 500 phytase units/kg.

In Exp. 2, 144 pigs were allotted to four dietary treatments, which were two levels of Zn as ZnO (0 or 2,000 ppm) and two levels of phytase (0 or 500 phytase units/kg) in a 2 x 2 factorial arrangement. At the end of Exp. 2, two pigs from each pen were selected randomly, and the posterior section of the tails was removed using a Stericut tail docker (Sharpvet, Cotran Corp., Ports-mouth, RI) for the determination of bone Zn concentration. The tails were autoclaved at 121°C for 30 min to facilitate removal of muscle, skin, and connective tissue. The coccygeal bones were then dried at 110°C for 24 h. A dry weight was determined, and bones were ashed at 500°C for 16 h. Ash samples were solubilized with 20% (vol/vol) HCl, heated, and diluted to a fixed volume. Samples were analyzed for Zn content using atomic absorption spectrophotometry (model 3030B, Perkin-Elmer, Norwalk, CT).

In Exp. 3, 168 pigs were allotted to four dietary treatments, which were as follows: 1) basal diet adequate in Ca and aP; 2) basal diet with Ca and aP levels reduced by 0.1%; 3) basal diet adequate in Ca and aP + 500 phytase units/kg; and 4) basal diet Ca and aP levels reduced by 0.1% + 500 phytase units/kg. Zinc oxide was added to all diets in Exp. 3 to provide 3,000 ppm Zn.

Blood Collection and Analyses
At the end of Exp. 1 and 2, and at the end of Phase 1 in Exp. 2, blood samples from each pig in a pen were collected via the anterior vena cava and placed in a 4-mL Vacutainer containing 8.0 mg of potassium oxalate and 10.0 mg of sodium fluoride (Sherwood Medical, St. Louis, MO). Pigs had access to feed before and during the bleeding period. Blood samples were refrigerated for 2 h, and then centrifuged for 20 min at 1,500 x g at 4°C. Plasma was collected and frozen until subsequent analysis for Zn. Plasma samples were pooled for pigs in a pen before analysis for Zn. Plasma Zn was determined by atomic absorption spectrophotometry as described previously for bone Zn.

Statistical Analyses
Data were analyzed as randomized complete block designs using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). In all experiments, data were analyzed with treatment and replication in the model. In Exp. 1, orthogonal contrasts appropriate for a 2 x 3 factorial arrangement of treatments were used to determine linear and quadratic effects of Zn, the main effect of phytase, and Zn x phytase interactions. In Exp. 2 and 3, treatment differences were determined with orthogonal contrasts for a 2 x 2 factorial arrangement of treatments. The pen of pigs served as the experimental unit for all data. Treatment differences were considered significant at = 0.10.

	Results

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Experiment 1
Performance and plasma Zn data for Exp. 1 are shown in Table 2. Average daily gain was linearly increased by Zn addition during Phase 1 (P = 0.01), Phase 2 (P = 0.09), and for the overall (P = 0.01) period. Similarly, ADFI was linearly increased by Zn addition during Phase 1 (P = 0.06), Phase 2 (P = 0.02), and for the overall (P = 0.02) period. Gain:feed was linearly increased (P = 0.01) by Zn only during Phase 1, and ADG, ADFI, and G:F were not affected by phytase addition during Phase 1. During Phase 2, phytase addition decreased ADG (P = 0.02) and G:F (P = 0.01), but the decrease in ADG was evident only in pigs fed excess Zn (Zn linear x phytase; P = 0.10). Gain:feed was decreased (P = 0.07) by phytase in the overall data. Plasma Zn was increased (quadratic, P = 0.01) as Zn level increased, but the response was much more pronounced at 2,000 ppm Zn than at 1,000 ppm Zn. The addition of phytase did not affect plasma Zn concentrations.

Experiment 3
Average daily gain, ADFI, and G:F were not affected by phytase supplementation during the Phase 1, Phase 2, or overall (Table 4). Decreasing the Ca and aP concentration in the diet, regardless of phytase addition, decreased (P = 0.02 to 0.10) ADG and G:F in Phase 2, and ADG, ADFI, and G:F were decreased for the overall data (P = 0.01 to 0.08).

	Discussion

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Plasma Zn concentrations were increased in pigs fed excess Zn compared with pigs fed the control diet. These results agree with those of Hahn and Baker (1993), who reported that plasma Zn was linearly increased when dietary concentrations of Zn were greater than 1,000 ppm were fed.

Coccygeal vertebrae Zn concentrations were increased by 2,000 ppm Zn. This response agrees with the work of LeMieux et al. (1996), who reported that excess Zn in the diet increased bone Zn concentrations in pigs weaned at 4 wk of age. Schell and Kornegay (1996) also reported that pigs fed pharmacological levels of Zn had higher bone Zn concentrations than did pigs fed a control diet.

Phytate, a compound found primarily in plant seeds, is a major etiological factor inhibiting the bioavailability of Zn. A negative effect of phytate on the availability of dietary Zn was first recognized by O’Dell and Savage (1960), who reported decreased absorption of Zn in chicks fed phytate. Inclusion of phytate in purified diets containing Zn fed to young male rats has been shown to decrease growth rate, feed intake, and to decrease Zn utilization (Davies and Nightingale, 1975). Davies and Nightingale (1975) suggested that Zn combines with phytate and Ca to form an insoluble Zn-Ca-phytate complex from which Zn is unavailable for absorption. Removal or reduction of phytate in some foods and feeds has increased the bioavailability of Zn in rats (Lönnerdal et al., 1988; Zhou et al, 1992), infant rhesus monkeys (Lönnerdal et al., 1988), and pigs (Bobilya et al., 1991). Ferguson et al. (1989) reported that a high phytate intake in East African children increased the risk of Zn deficiency. These data suggest that the bioavailability of Zn in foods and feeds is a function of its phytate concentration. The dietary level of Zn in these studies was at or near the requirement, and none evaluated pharmacological levels of Zn.

Phytase is an enzyme that catalyses the stepwise removal of inorganic orthophosphate from phytate (Ravindran et al., 1995). Dietary phytase addition has improved the availability of phytate-bound P, reduced P excretion, and improved growth performance in both pigs (Näsi, 1990; Yi et al., 1996b; Murry et al., 1997) and poultry (Simons et al., 1990; Sebastian et al., 1996; Cabahug et al., 1999). Phytase also has increased the bioavailability of Zn in pigs (Lei et al., 1993; Adeola et al., 1995) and chicks (Sebastian et al., 1996; Yi et al., 1996a; Zanini and Sazzad, 1999) fed diets containing adequate or low concentrations of Zn. The increase in Zn bioavailability by phytase may decrease the need for excess Zn supplementation, thereby decreasing the quantity of Zn excreted in the feces, which may become an environmental concern.

In our experiments, phytase did not affect growth performance of pigs in Phase 1, regardless of the level of dietary Zn; however in Phase 2, the response to phytase was inconsistent. In one experiment, phytase eliminated the beneficial effect of excess Zn, but in another experiment, phytase enhanced the effect of Zn. We have no explanation for this variable response. Augspurger et al. (2003) reported that pharmacological levels of Zn decreased the efficacy of phytase.

Phytase did not affect plasma Zn concentrations. These results agree with those of Roberson and Edwards (1994) and Sebastian et al. (1996), who reported no change in plasma Zn concentrations from phytase supplementation. The authors suggested that phytase does not affect plasma Zn concentration when Zn is nutritionally adequate in the diet. Similarly, Adeola et al. (1995) and Lei et al. (1993) reported that phytase increased plasma Zn concentrations when added to diets containing no supplemental Zn; however, supplemental phytase did not increase plasma Zn concentrations when Zn was supplemented to the diets.

Phytase did not affect bone Zn concentrations. We are not aware of other research that has evaluated the effects of phytase on bone Zn concentration in pigs. However, phytase has increased (Roberson and Edwards, 1994; Yi et al., 1996a; Zanini and Sazzad, 1999) or had no effect (Sebastian et al., 1996) on bone Zn concentration in chicks.

Phytate is known to form complexes with minerals such as Zn, thereby decreasing their availability to the animal (Vohra et al., 1965). The hydrolysis of phytate would be expected to increase Zn availability. However, in the present study, supplementation of phytase to diets containing pharmacological concentrations of Zn did not affect plasma or bone Zn concentrations.

Phytase is not effective in improving Zn availability of weanling pigs fed diets containing excess Zn (as ZnO). Phytase also inconsistently affected growth performance of nursery pigs, and it does not seem to be as efficacious as in diets for growing-finishing pigs.

	Footnotes

 
¹ Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as Manuscript No. 03-18-1367.

² The authors thank F. M. LeMieux and the Louisiana State Univ. Agric. Center Swine Unit for assistance with the animals and A. C. Guzik, J. O. Matthews, J. L. Shelton, B. C. Watson, and R. L. Payne for assistance with data collection and laboratory analyses.

³ Correspondence—e-mail: lsouthern{at}agctr.lsu.edu

Received for publication June 4, 2004. Accepted for publication November 4, 2004.

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