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Effects of replacing pharmacological levels of dietary zinc oxide with lower dietary levels of various organic zinc sources for weanling pigs^1,2

NCR-42 Committee on Swine Nutrition^4,5

	Abstract

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Two 28-d randomized complete block design experiments were conducted to evaluate the effects of concentrations and sources of Zn on growth performance of nursery pigs. Seven stations participated in Exp. 1, which evaluated the efficacy of replacing 2,500 ppm of Zn from ZnO with 125, 250, or 500 ppm of Zn from Zn methionine. A control diet with 125 ppm of supplemental Zn was included at all stations. A total of 615 pigs were used in 26 replicates. Average weaning age was 20.6 d and the average initial BW was 6.3 kg. There were no differences in any growth response among the three supplemental Zn methionine levels fed in Exp. 1. Zinc supplementation from Zn methionine improved ADG compared with the control during all phases (P < 0.05), due primarily to an increase in ADFI. Pigs fed 2,500 ppm of Zn from ZnO gained faster (P < 0.01) than those fed the control diet during all phases, and faster (P < 0.05) than those fed supplemental Zn from Zn methionine for the 28-d experiment. Differences in gain were again due mainly to differences in feed intake. A second experiment compared five sources of supplemental organic Zn (500 ppm of Zn) with 500 and 2,000 ppm supplemental Zn from ZnO and a control (140 ppm total Zn). Six stations used a total of 624 pigs, with an average weaning age of 20.4 d and averaging 6.2 kg BW in 15 replicates. Pigs fed 2,000 ppm of Zn from ZnO gained faster (P < 0.05) than pigs fed the control or any of the 500 ppm of Zn treatments (ZnO or organic Zn). Pigs fed the 2,000 ppm of Zn from ZnO also consumed more feed than those receiving 500 ppm of Zn from ZnO or from any of the organic Zn sources (P < 0.05). Organic sources of Zn did not improve gain, feed intake, or feed efficiency beyond that achieved with the control diet. Supplemental Zn at a concentration of 500 ppm, whether in the form of the oxide or in an organic form, was not as efficacious for improved ADG as 2,000 to 2,500 ppm of Zn from ZnO.

Key Words: Organic Zinc • Weanling Pigs • Zinc

	Introduction

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During the late 1980s, it was discovered that feeding pharmacological concentrations of ZnO to weanling pigs resulted in reduced diarrhea and increased growth rates (Poulsen, 1989). Subsequent research demonstrated that dietary levels of 2,000 to 4,000 ppm of Zn from ZnO enhanced pig growth responses even when scours were not a problem in weaned pigs (Poulsen, 1995; Smith et al., 1997; Hill et al., 2000). It also was suggested that ZnO was the only inorganic form of Zn that produced these results (Hahn and Baker, 1993; McCully et al., 1995; Schell and Kornegay, 1996). Recent data have indicated that organic Zn sources can be added to pig nursery diets at dietary concentrations below the pharmacological concentrations of ZnO commonly used in pig starter diets and still produce similar growth performance benefits (Ward et al., 1997; Fakler, et al., 1998; Case and Carlson, 2002). Lower concentrations of added dietary Zn would lessen the environmental risk from soil application of swine manure.

The objective of this research was to further evaluate the efficacy of lower levels (500 ppm) of Zn from several organic sources of Zn compared with pharmacological levels (2,000 to 2,500 ppm) of inorganic Zn from ZnO on performance of weanling pigs.

	Materials and Methods

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Two experiments were conducted by the North Central Regional (NCR-42) Swine Nutrition Committee. All stations followed procedures approved by their respective animal care and use committees.

Experiment 1

The first experiment evaluated the efficacy of replacing 2,500 ppm of Zn from ZnO (Prince Agri Products, Inc., Quincy, IL) with 125, 250, or 500 ppm concentrations of Zn from Zn methionine (Zinpro 100, Zinpro, Inc., Eden Prairie, MN). The feed-grade ZnO was a standard commercial product (Zinc Nacional S.A., Monterrey, Mexico) manufactured by the Waelz process (Mavromichalis et al., 2000), with a guaranteed concentration of 72% Zn. A control treatment, which contained only the Zn present in the trace mineral premix was included. Zinc sources in the trace mineral premix varied among stations.

Seven university research stations participated in the study (IL, KY, MI, MO, OH, OK, and WI). One station conducted their study at two different sites with different facilities. This was considered as an additional test station for a total of eight locations. The experiment was conducted as a randomized complete block design with 26 replicates. Each station conducted a minimum of two replicates at each site. Management and facility design varied by station, but the procedures followed were the same within each replicate. A total of 615 crossbred pigs of various genetic crosses were weaned at an average age of 20.6 d, with an initial average BW of 6.3 kg. Pigs were allotted to treatment pens based on BW, sex, and litter, with an equal number of pigs allotted to treatment pens within each replicate. Pigs were housed in completely enclosed nursery facilities that contained either wire mesh or plastic-covered wire mesh floors, with room temperatures adjusted as needed to meet the comfort zone of the pig. Information and overall performance responses for each station are shown in Table 1.

Because of the better performance of the ZnO treatment group relative to the Zn methionine groups of Exp. 1, and because other organic Zn sources may respond differently in weaned pigs, a second experiment was conducted to evaluate the efficacy of various organic Zn sources compared with a feed-grade ZnO. The five commercially available organic Zn sources used were from each of the categories identified by AAFCO (2002). The Zn sources selected for this experiment are shown in Table 3.

The experiment was conducted as a randomized complete block design in 15 replicates with each station conducting a minimum of two replicates. A total of 624 crossbred pigs with an average weaning age of 20.4 d and averaging 6.2 kg BW was used in the trial. The experiment was conducted at six research stations (MI, MO, OH, SD, TX, and WI) using similar facilities and genotypes as in Exp. 1. Management and pig allotment procedures were similar to those in Exp. 1. Details of the facilities and overall pig performance responses for each of the research stations are reported in Table 1.

Zinc Analysis

Samples of all diets were sent to one laboratory for Zn analysis. The atomic absorption spectrophotometry method used followed AOAC (1995) procedures.

Statistical Analyses

The data from both experiments were analyzed using the ANOVA procedures outlined by Steel and Torrie (1980), with the GLM procedures of SAS (SAS Inst., Inc., Cary, NC). In both experiments, the pen was considered the experimental unit for all measurements. The statistical model included station, replicate within station, treatment, station x treatment, and residual. Station and treatment effects were tested with the station x treatment term, and the interaction was tested with the residual. Preplanned treatment contrasts in Exp. 1 were the control diet vs. the mean of all other diets; the ZnO treatment vs. the mean of the Zn methionine treatments; linear and quadratic regressions within the three Zn methionine treatments; and the 500 ppm of Zn methionine diet vs.the positive control (2,500 ppm from ZnO) diet. In Exp. 2, preplanned contrasts were control vs. the mean of the other treatment groups; the 2,000 ppm ZnO diet vs. the mean of the 500 ppm Zn levels from ZnO and the five organic Zn sources; and the 500 ppm Zn oxide diet vs. each of the five organic Zn sources. A probability level of P < 0.05 was considered statistically significant.

	Results

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As expected, there were rather large differences among stations (P < 0.001) with respect to ADG, ADFI, and G:F in both experiments, as shown in Table 1. In some instances, the station x treatment interaction was significant, but this was always due to differences in the magnitude of the responses to Zn.

Experiment 1

The effects of replacing 2,500 ppm added Zn from ZnO with varying concentrations of added Zn from Zn methionine are summarized in Table 4. During the initial 7-d period, there were no treatment differences in ADG, ADFI, or G:F (data not shown).

From 14 to 28 d of the experiment, pigs fed Zn from Zn methionine gained faster and consumed more feed when compared with those fed the control diet (P < 0.05). During this period, pigs fed the 2,500 ppm of added Zn from ZnO consumed more feed (P < 0.05) and gained faster (P < 0.05) than those fed the three lower levels of Zn methionine. Gain:feed ratio was not affected by dietary Zn addition.

During the entire 28-d experimental period, pigs fed Zn from Zn methionine gained faster (P < 0.05) and consumed more feed (P < 0.05) than pigs fed the control diet, but G:F was unaffected by either source of Zn addition (oxide or methionine). Zinc oxide addition at 2,500 ppm resulted in faster gain (P < 0.05) and greater feed intake (P < 0.05) than Zn methionine addition fed at any level. No difference was observed in efficiency of feed utilization between Zn sources during the overall 28-d period. There was no difference in responses among pigs fed the three concentrations of Zn methionine. Pigs fed 500 ppm of Zn from Zn methionine gained slower than pigs fed 2,500 ppm of Zn from ZnO (P < 0.05), but there was no difference in feed intake or G:F.

Experiment 2

The effects of replacing 500 or 2,000 ppm added Zn from ZnO with 500 ppm added Zn from various organic Zn sources are summarized in Table 5. As in Exp. 1, there were no treatment differences during the initial 7-d period (data not shown).

Over the 28-d experimental period, pigs fed 2,000 ppm of added Zn from ZnO gained faster (P < 0.05) and consumed more feed (P < 0.05) than those fed 500 ppm of added Zn from ZnO or any of the organic sources. Feed efficiency was not affected by dietary Zn addition during any phase of this 28-day study.

In this study, only pigs fed 2,000 ppm of Zn from ZnO had improved gain and feed intake over the controls. Organic sources of Zn did not improve ADG, ADFI, or G:F beyond that achieved with the control diet.

	Discussion

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Results of these two studies indicate that feeding pharmacological concentrations (2,000 or 2,500 ppm) of inorganic Zn from ZnO improves the growth rate of weanling pigs compared with pigs receiving the control diet or 500 ppm of added Zn from ZnO or any organic source, which supports the findings of Hahn and Baker (1993), Carlson et al. (1999), and Hill et al. (2000). However, these findings are in contrast to those of Ward et al. (1996), who reported that supplementing starter pig diets with 250 ppm of Zn from Zn methionine gave equal performance to 2,000 ppm of Zn from ZnO when both diets were supplemented with 160 ppm of Zn from ZnSO₄. Also, Fakler et al. (1998) suggested that performance by pigs fed organic AA complexes may be improved over those pigs fed standard inorganic sources, but their study employed nutrient levels (80 to 100 ppm added), not pharmacological levels, of Zn. Woodworth et al. (1999) noted that gain was not improved by a Zn AA complex compared with pharmacological concentrations of ZnO.

In Exp. 1, ADG and ADFI were improved by both sources of Zn (ZnO and Zn methionine) compared with the controls during the 14- to 28-d period and for the entire experiment; however, pigs fed ZnO were superior for these criteria compared with those fed Zn methionine. Although the exact mechanisms of performance enhancement from Zn are unknown, it has been suggested that the effect is in the intestine, probably involving the microflora, and that the solubility of Zn compounds affect efficacy (Poulsen, 1995; Cromwell, 2001). It can be theorized that the lower solubility of ZnO compared with Zn methionine is the reason for the better performance of ZnO fed pigs in this trial, but fecal excretion data reported by Case and Carlson (2002) argue against this hypothesis. They reported that fecal excretion of Zn did not differ among pigs fed ZnO or two organic Zn sources at 500 ppm of dietary Zn.

For the overall 28-d period, there was no improvement in G:F. Poulsen (1995) and Smith et al. (1997), although reporting an increase in growth rate for weanling pigs fed pharmacological amounts (2,500 or 3,000 ppm of Zn from ZnO) of Zn, found no improvements in feed intake. Hill et al. (2000) found both improved ADG and ADFI during various phases of their 28-d study when 3,000 ppm of Zn as the oxide was fed. Case and Carlson (2002) found no improvement in ADFI over a 28-d period for pigs receiving 500 ppm of Zn from two different organic sources.

In Exp. 2, gain and feed intake were improved when pigs were fed 2,000 ppm of Zn as the oxide compared with those fed any of the organic Zn sources; however, for the overall 28-d period, Zn source did not affect feed efficiency. Pouslen (1995) and Smith et al. (1997) found no improvement in feed efficiency from Zn in a 28-d trial. Hill et al. (2001) reported a quadratic response in feed efficiency to increasing concentrations of Zn (0 to 3,000 ppm of Zn added as ZnO) during a 28-d trial. It is obvious that the gain response to pharmacological levels of Zn is more uniform, and is almost always positive, whereas the response in feed efficiency is quite variable.

Although pig performance improves from feeding pharmacological concentrations of Zn as ZnO, there are environmental concerns associated with high concentrations of Zn in manure (Carter et al., 2002; Meyer et al., 2002; Rincker et al., 2002). Martinez et al. (2002) reported that pigs fed 2,000 ppm of Zn as ZnO excreted 203 mg of Zn/d for the first 14 d after weaning. Rincker et al. (2002) reported that total Zn excretion was similar when 2,000 ppm of Zn was fed as oxide or methionine, but urinary Zn was a greater component when Zn methionine was fed compared with ZnO. The data reported by Case and Carlson (2002) indicate that in excess of 99% of the Zn is excreted in the feces, regardless of source (ZnO or organic Zn) or dietary level (150, 500, or 3,000 ppm). Similarly, Meyer et al. (2002) showed that short-term feeding of Zn to the nursery pig resulted in Zn excretion equal to that of a grower-finisher pig fed 100 ppm of Zn. The previous NCR-42 Zn study (Hill et al., 2000) showed that feeding 1,500 ppm of Zn was as efficacious as 3,000 ppm and would obviously decrease Zn excretion by approximately half.

Supplemental Zn at 500 ppm from ZnO or several organic sources was not as effective in stimulating growth, feed intake, or efficiency as when a pharmacological (2,000 ppm) level of Zn was fed as ZnO. It is imperative to understand the mechanism(s) involved in the growth promotion efficacy provided by pharmacological concentrations of Zn in the form of ZnO to minimize the amount of Zn excreted into the environment.

	Footnotes

 
¹ Appreciation is extended to Akey, Inc., Lewisburg, OH 45338 for supplying the zinc premixes for this study.

² Each station followed the approved experimental procedures for their respective animal care committees.

⁴ Affiliation of authors at the time of the study: G. R. Hollis, Univ. of Illinois, Urbana; S. D. Carter, Oklahoma State Univ., Stillwater; T. R. Cline, Purdue Univ., West Lafayette, IN; T. D. Crenshaw, Univ. of Wisconsin, Madison; G. L. Cromwell, Univ. of Kentucky, Lexington; G. M. Hill, Michigan State University, East Lansing; S. W. Kim, Texas Tech Univ., Lubbock; A. J. Lewis, Univ. of Nebraska, Lincoln; D. C. Mahan, The Ohio State Univ., Columbus; P. S. Miller, Univ. of Nebraska, Lincoln; H. H. Stein, South Dakota State Univ., Brookings; and T. L. Veum, Univ. of Missouri, Columbia.

⁵ Other members of the NCR-42 Committee at the time the trial was conducted: R. C. Ewan, Iowa State Univ., Ames; J. L. Nelssen, Kansas State Univ., Manhattan; G. C. Shurson, Univ. of Minnesota, St. Paul; and J. T. Yen (deceased), ARS-USDA, Clay Center, NE. The administrative advisor during the conduct of the study was R. A. Easter, Univ. of Illinois, Urbana.

³ Correspondence: Dept. of Anim. Sci., Purdue Univ., West Lafayette, IN 47907-2054 (phone: 765-494-4846; fax: 765-494-9346; e-mail: tcline{at}purdue.edu).

Received for publication October 7, 2004. Accepted for publication May 25, 2005.

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