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Effect of microbial phytase addition with or without the trace mineral premix in nursery, growing, and finishing pig diets^1,2

J. L. Shelton^*, F. M. LeMieux, L. L. Southern^*,3 and T. D. Bidner^*

^* Department of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803-4210; and and Department of Agriculture, McNeese State University, Lake Charles, LA 70609

	Abstract

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Two experiments were conducted to determine the interactive effects of phytase with and without a trace mineral premix (TMP) in diets for nursery, growing, and finishing pigs on growth performance, bone responses, and tissue mineral concentrations. Pigs (initial and final BW of 5.5 and 111.6 kg [Exp. 1] or 5.4 and 22.6 kg [Exp. 2]) were allotted to treatments on the basis of BW with eight (Exp. 1) or six (Exp. 2) replications of six or seven pigs per replicate pen. Pigs were started on the diets the day of weaning (average of 18 d). In both experiments, the treatments were with or without 500 phytase units/kg of diet and with or without the TMP in a 2 x 2 factorial arrangement. The Ca and available P concentrations were decreased by 0.10% in diets with phytase. The nursery phase consisted of Phase I (7 d), Phase II (14 d), and Phase III (13 d) periods. In Exp. 1, 26 of 52 pigs fed the diet without the TMP and without phytase had severe skin lesions and decreased growth performance; therefore, pigs fed this diet were switched to the positive control diet. In Exp. 2, the treatment without the TMP and without phytase had 12 replications instead of six. At the end of Phase III, half these replications were switched to the positive control diet and half were switched to the diet without the TMP but with phytase. In Exp. 1 during Phases II and III and in the overall data, pigs fed the diet without the TMP had decreased ADG and ADFI, but the addition of phytase prevented these responses (phytase x TMP; P < 0.02). Growth performance was not affected by diet during the growing-finishing period. Coccygeal bone Zn and Na concentrations were decreased (P < 0.09) in pigs fed the diet without the TMP, and adding phytase increased (P < 0.03) Zn and Fe concentrations. In Exp. 2 during Phases I and II, pigs fed the diet without the TMP had decreased ADG, but the addition of phytase prevented this response (phytase x TMP; P < 0.10). Pigs fed the diet without the TMP had decreased (P < 0.10) ADG (Phase II and overall), ADFI (Phases II and III and in the overall data), and G:F (Phase III). Coccygeal bone Zn and Cu concentrations were decreased (P < 0.09) in pigs fed the diet without the TMP, and adding phytase increased (P < 0.03) Zn concentration in the bones. These data indicate that removing the TMP in diets for nursery pigs decreases growth performance and bone mineral content, and that phytase addition to the diet without the TMP prevented the decreased growth performance.

Key Words: Bone Mineral • Growth • Phytase • Pigs • Trace Minerals

	Introduction

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Research has been conducted on the effects of removing the trace mineral premix (TMP) in diets for swine; however, most of the research used growing or finishing pigs. Kim et al. (1997) and Mavromichalis et al. (1999) indicated that the TMP could be removed from the diet of finishing pigs with no negative effects on growth, carcass characteristics, or pork quality. Shelton et al. (2004) reported similar results on growth performance and pork quality with growing-finishing pigs (22 to 109 kg), but there were some negative effects on carcass traits. We are not aware of research on removing the TMP in diets for nursery pigs.

Phytate forms insoluble salts with Fe, Zn, Mn, and Cu (Vohra et al., 1965). Phytase, an enzyme that breaks down phytate (Gibson and Ullah, 1990), has been shown to increase the absorption and retention of Zn and Cu (Lei et al., 1993; Adeola et al., 1995). Therefore, phytase may be able to replace the TMP in swine diets and result in equal growth performance relative to pigs fed diets with the TMP.

Thus, the objective of these experiments was to determine the effect of phytase with and without the TMP in diets for nursery, growing, and finishing pigs on growth performance, bone ash percent and strength, and tissue mineral concentrations.

	Materials and Methods

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General
Methods used in these experiments related to animal care were approved by the Louisiana State University (LSU) Agricultural Center Animal Care and Use Committee.

Two experiments were conducted with Yorkshire x Landrace and Yorkshire x Duroc barrows and gilts to determine the effect of phytase with and without the TMP in diets for nursery, growing, and finishing pigs. During the nursery period, pigs were housed in total confinement in an environmentally controlled modular building, in 0.97-m x 1.47-m pens with plastic slotted floors and an under-floor flush system. During the growing period, pigs were housed in total confinement in 1.2-m x 2.4-m pens with metal-slatted floors. During the finishing period, pigs were housed in total confinement in an open-sided finishing barn with 1.5-m x 3.0-m pens with concrete-slatted floors. Pigs and their environment were monitored twice daily.

Natuphos 1200 (BASF Corp., Mount Olive, NJ), when included in the diet, was added at 0.033% (as-fed basis), which provided 500 phytase units/kg of diet. Analysis of the Natuphos 1200 indicated an activity of 1,515 phytase units/kg of premix. The Ca and available P (aP) were decreased by 0.10% in all diets with phytase. Values for the AA and minerals for all ingredients were taken from NRC (1998). All diets and water were provided for ad libitum consumption and the feed was in mash form.

Experiment 1
Nursery Period.
Two hundred eight barrows and gilts with an average initial BW of 5.5 kg were used in this experiment. They were weaned at an average age of 18 d, and the treatment diets were started on the day of weaning. The pigs were allotted to treatments on the basis of weight in a randomized complete block design. Ancestry was equalized as much as possible. There were three replications of gilts and five replications of barrows, with six or seven pigs per replicate pen.

The four dietary treatments in a 2 x 2 factorial arrangement (Table 1) were as follows: 1) corn-soybean meal (C-SBM) control diet; 2) C-SBM diet with 500 phytase units/kg of diet; 3) C-SBM diet without the TMP; and 4) C-SBM diet without the TMP and with 500 phytase units/kg of diet. Actual analysis of the diets with phytase indicated that Diet 2 provided 609 phytase units/kg of diet and Diet 4 provided 602 phytase units/ kg of diet. The diets were formulated to contain 1.60, 1.40, and 1.20% total Lys; 0.90, 0.80, and 0.70% Ca; and 0.55, 0.40, and 0.32% aP for Phases I, II, and III, respectively. All other AA met or exceeded the ratio to Lys (NRC, 1998). The nursery phase consisted of a Phase I (7 d), Phase II (14 d), and Phase III (13 d) period.

Growing-Finishing Period.
At the end of Phase III, the 72 gilts were continued on the project. The gilts were re-allotted within treatment on the basis of BW in a randomized complete block design. There were four (Treatments 3 and 4) or five (Treatments 1 and 2) replications with four gilts per replicate pen. Their BW at the end of Phase III was 16.2 kg, and the final BW was 111.6 kg. The dietary treatments were the same as in the nursery period, except that pigs fed the diet without the TMP and without phytase during the nursery period were fed the control diet during the growing-finishing period. Skin lesions occurred on 26 of 52 pigs, and it was clear that many of these pigs would have died without a diet change. A four-phase growing-finishing program was used, and diets (Table 1) were formulated to provide 0.97, 0.88, 0.79, and 0.68% total Lys for BW ranges of 20 to 43, 43 to 66, 66 to 89, and 89 to 112 kg, respectively. All AA met a minimum of 105% of the AA requirement according to each growth phase for gilts gaining 325 g of carcass fat-free lean per day, as calculated using the NRC (1998) model. The diets also were formulated to contain 0.60% Ca and 0.24% aP in the early-growing phase, 0.53% Ca and 0.19% aP in the late growing phase, 0.48% Ca and 0.17% aP in the early-finishing phase, and 0.45% Ca and 0.15% aP in the late finishing phase. The aP level was only decreased to 0.053% during the late finishing period. Actual analysis of the diets for phytase indicated that Diet 2 provided 575 phytase units/kg of diet and Diet 4 provided 470 phytase units/kg of diet.

On the day after the growth trial ended, two pigs per replicate pen were randomly selected and slaughtered by exsanguination after electrical stunning. At slaughter, liver and kidneys were weighed, sampled (approximately 20 g), and the samples were frozen at –20°C until analysis. In addition, samples of bile, pancreas, and LM (between the 9th and 10th ribs) were taken and frozen at –20°C until analysis. Samples of liver, kidney, pancreas, and muscle were analyzed for dry ash percent and mineral content as previously described for the coccygeal bones at the end of the nursery phase. Mineral content of bile was determined after drying in an oven at 100°C for 24 h and digesting in nitric acid and hydrogen peroxide. Mineral content of the liver, kidney, pancreas, and muscle samples was determined on the ash after dissolving in nitric acid and hydrogen peroxide as previously described. The 3rd and 4th metacarpal bones from the left foot of each pig were removed and manually cleaned of adhering tissue. The 3rd metacarpal was used to determine bone ash percent and bone mineral content, as previously described (except that the bones were ashed for 36 h), after being extracted of fat (Soxhlet, Labglass, Vineland, NJ) and redried. The 4th metacarpal was broken using a HD 250 texture machine (Texture Technologies Corp., Scarsdale, NY) fitted with three-point bend rig, with a load cell capacity of 250 kg and crosshead speed of 100 mm/min and a span over which the bone was set of 1.5 cm.

Experiment 2
Nursery Period.
During the nursery period, Exp. 2 was conducted exactly as Exp. 1 with the following exceptions. One hundred eighty-five barrows and gilts with an average initial BW of 5.4 kg were used. The pigs were allotted to the same four dietary treatments as in Exp. 1, but had three replications of gilts and three replications of barrows, with six or seven pigs per replicate pen. However, the diet without the TMP and without phytase had 12 replicate pens (six gilt pens and six barrow pens) because at the end of the nursery period, six replicate pens were fed the diet with the TMP, whereas the other six replicate pens were fed the diet without the TMP but with phytase. Actual analysis of the diets with phytase indicated that Diet 2 provided 646 phytase units/kg of diet and Diet 4 provided 631 phytase units/kg of diet. At the end of Phase III, tails were removed from two pigs per pen for determination of coccygeal bone mineral content as previously described.

Early-Growing Period.
At the end of Phase III, pigs were moved to a growing facility and fed until the growth rate of pigs previously fed the diet without the TMP and without phytase, but switched to the positive control diet, was similar to the growth rate of pigs fed the positive control diet. The BW of the pigs at the end of the Phase 3 period was 16 kg, and the final BW of the pigs was 22 kg. Three replicate pens of gilts and three replicate pens of barrows fed the diet without the TMP and without phytase for the nursery period were fed the control diet for the early-growing period. The other three replicate pens of gilts and three replicate pens of barrows fed the diet without the TMP and without phytase for the nursery period were fed the diet without the TMP, but with phytase added, for the early-growing period. The diets (Table 1) were formulated as previously described for the early-growing period in Exp. 1.

Statistical Analyses
Data were analyzed as a randomized complete block design using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). For the nursery data in Exp. 1 and 2, the statistical model included treatment and replication. Orthogonal contrasts appropriate for a 2 x 2 factorial arrangement of treatments were used to determine treatment effects. For the growing-finishing data in Exp. 1, the statistical model included treatment and replication, and treatments were compared with the PDIFF option in SAS when the overall treatment effects were different (P = 0.10). For the early-growing data in Exp. 2, the statistical model included treatment, replication, and sex, and treatments were compared with the PDIFF option in SAS. Treatment differences were considered significant at = 0.10. The pen of pigs served as the experimental unit for all data.

	Results

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Experiment 1
Nursery Period.
Average daily gain during Phase III and overall, and ADFI during Phases II, III, and overall were decreased in pigs fed the diet without the TMP, but phytase addition prevented these responses (phytase x TMP; P < 0.02; Table 2). Similarly, ADG during Phase II was decreased in pigs fed the diet without the TMP, and phytase addition partially prevented the response, but the interaction was not significant. The G:F was not affected by diet. Skin lesions occurred on 26 of 52 pigs fed the diets without the TMP and without phytase.

Early-Growing Period.
During the early-growing period, ADG and G:F were decreased (P < 0.07) in pigs fed the diet without the TMP and with added phytase relative to pigs fed the diet without the TMP for the nursery period and that diet with phytase added during the early-growing period (Table 7). Gain:feed was decreased (P = 0.07) in pigs fed the control diet during the nursery and early-growing periods relative to pigs fed the diet without the TMP for the nursery period and that diet with added phytase for the early-growing period.

	Discussion

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In our experiments, 26 out of 52 (Exp. 1) and 4 out of 37 (Exp. 2) pigs that were fed the diet without the TMP and without phytase developed skin lesions starting at the end of Phase II. Feeding pigs diets deficient in Zn can lead to parakeratosis (Luecke, 1984). Skin problems did not develop on pigs fed the diet without the TMP and with phytase, indicating that phytase released enough Zn to overcome signs of parakeratosis. However, in Exp. 2, the skin problems that developed in Phase II were not evident by the end of Phase III, and growth performance during Phase III was not affected by diet, indicating that pigs in Exp. 2 overcame the mineral deficiency during Phase III. This response could have been due to a slightly increased ADFI by the pigs in Exp. 2 (465 and 545 g/d in pigs fed the diet without the TMP for Exp. 1 and 2, respectively).

Shelton et al. (2004) reported that adding phytase or removing the TMP during the growing-finishing period had no effect on bone strength or bone ash percent relative to pigs fed a control diet. In the current study, however, bone strength was decreased in gilts fed the diet without the TMP but with phytase.

Shelton et al. (2004) reported an increase in liver weight in growing-finishing pigs fed diets without the TMP or with reduced Ca and P, but adding phytase decreased liver weight to that of the pigs fed the control diet. In our study, liver weight was numerically increased in pigs fed the diet without the TMP and without phytase for the nursery period followed by the control diet for the growing-finishing periods (1,828 and 1,700 g for pigs fed the diet without the TMP for the nursery period and the control diet for the growing-finishing period relative to those fed the diet without the TMP and with added phytase for the nursery and growing-finishing periods, respectively). This numerical increase indicates that decreasing the trace minerals in the diet might result in an increase in liver weight.

Kornegay and Qian (1996), O’Quinn et al. (1997), and Shelton et al. (2004) reported that adding phytase (300 to 1,400 phytase units) to low Ca and P diets increased bone ash percent equal to that of a control diet. Shelton et al. (2004) also reported that adding phytase and reducing the Ca and aP by 0.10% each to diets with or without TMP had no effect on bone ash percent when the diets were fed from 22 to 109 kg. However, in the current study, pigs were fed the diets from 6 to 112 kg, and bone ash percent was decreased in pigs fed diets with phytase compared with pigs fed the control diet. This response suggests that the phytase addition did not completely replace the 0.10% additions of Ca and/ or aP when diets are initiated at 18 d of age.

We have no explanation for the increase in coccygeal bone ash percent in pigs fed the diet without the TMP and without phytase (Exp. 1), but the Ca concentration in the coccygeal bones also was increased in pigs fed diets without the TMP and without phytase. Adding phytase prevented these responses in Exp. 1; however, these responses were not observed in Exp. 2.

Feeding diets with added phytase or without the TMP to nursery pigs had variable effects on mineral content in the coccygeal bones. In both experiments, feeding diets without the TMP resulted in a decrease in Zn concentration in the coccygeal bones, and adding phytase prevented this response, which agrees with previous research indicating that phytase increases the availability of Zn in diets for pigs (Lei et al., 1993; Adeola et al., 1995). In Exp. 1, Fe concentration in the coccygeal bones was increased when phytase was added to the diet, but in Exp. 2, Fe concentration in the coccygeal bones was not affected by phytase addition, and tissue Fe concentrations were not affected in growing-finishing gilts fed the diet without the TMP and with phytase for the growing-finishing period. Stahl et al. (1999) reported that phytase addition increased Fe availability in young pigs. The differences between our two experiments in Fe concentrations in the coccygeal bones of nursery pigs may be explained by the slight increase in ADFI in Exp. 2. The Cu concentration in the coccygeal bones was decreased in pigs fed the diet without the TMP in Exp. 2, but it was not affected in Exp. 1. Adding phytase had no effect on bone Cu concentration, which disagrees with the findings of Adeola et al. (1995), who reported that the addition of phytase increased Cu absorption and retention. In Exp. 2, Mn concentration in the coccygeal bones was increased when phytase was added to the control diet. Removing the TMP from the diet increased bone Mn concentration relative to the control diet, and adding phytase decreased bone Mn concentration. These responses indicate that there may be a Zn x Mn interaction, as discussed by Shelton et al. (2004); however, this response was not observed in Exp. 1.

Tissue Zn concentrations were not affected in gilts fed the diet without the TMP and with phytase for the growing-finishing period. Removing the TMP and adding phytase to the diets of growing-finishing gilts resulted in a decrease in Cu concentration in the bile and muscle relative to those fed the control diet. Shelton et al. (2004) reported a decrease in Cu concentration in the bile and liver and numerical decreases in the Cu concentration in the bones of pigs fed a diet without the TMP and with added phytase relative to a control diet for the growing-finishing periods. Edmonds and Arentson (2001) and Shaw et al. (2002) indicated that removing the vitamin and TMP during the finishing period had no effect on Cu, Fe, or Zn concentrations in the LM.

Removing the TMP and adding phytase to the diets of growing-finishing gilts also resulted in a decrease in Ca, P, Na, Mg, and K concentrations in the bone, and Na concentration in the pancreas and an increase in Mn concentrations in the bile and bone relative to those fed the control diet. Shelton et al. (2004) reported a decrease in the Na, Mg, and K concentrations in the bone of pigs fed a diet without the TMP and with phytase for the growing-finishing periods.

These data indicate that removing the TMP in the diets for nursery pigs results in negative growth performance; however, adding phytase to the diets without the TMP resulted in growth performance equal to that of pigs fed the control diet. Adding phytase and/or removing the TMP had variable effects on tissue mineral concentrations.

Use of phytase may be able to decrease the total dietary requirement for trace minerals to the extent that a TMP is not needed. Further research is needed to determine the effect of phytase addition to diets without the TMP in nursery to finishing pig diets on pork quality and human health.

	Footnotes

 
¹ Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as Manuscript No. 04-18-0092.

² The authors thank the Louisiana State Univ. Agric. Center Swine Unit and the Louisiana State Univ. Agric. Center Meats Lab. for assistance with data collection. The authors also thank M. Persica, J. Carothers, A. Guzik, R. Payne, D. Dean, R. Lirette, B. Watson, and T. O’Connor-Dennie for assistance with data collection and laboratory analyses.

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

Received for publication April 8, 2004. Accepted for publication November 4, 2005.

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