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ANIMAL NUTRITION |
Department of Animal Science, University of Missouri, Columbia 65211
Abstract
Three experiments were conducted to evaluate the effects of feeding dietary concentrations of organic Zn as a Zn-polysaccharide (Quali Tech Inc., Chaska, MN) or as a Zn-proteinate (Alltech Inc., Nicholasville, KY) on growth performance, plasma concentrations, and excretion in nursery pigs compared with pigs fed 2,000 ppm inorganic Zn as ZnO. Experiments 1 and 2 were growth experiments, and Exp. 3 was a balance experiment, and they used 306, 98, and 20 crossbred pigs, respectively. Initially, pigs averaged 17 d of age and 5.2 kg BW in Exp. 1 and 2, and 31 d of age and 11.2 kg BW in Exp. 3. The basal diets for Exp. 1, 2, and 3 contained 165 ppm supplemental Zn as ZnSO4 (as-fed basis), which was supplied from the premix. In Exp. 1, the Phase 1 (d 1 to 14) basal diet was supplemented with 0, 125, 250, 375, or 500 ppm Zn as Zn-polysaccharide (as-fed basis) or 2,000 ppm Zn as ZnO (as-fed basis). All pigs were then fed the same Phase 2 (d 15 to 28) and Phase 3 (d 29 to 42) diets. In Exp. 2, both the Phase 1 and 2 basal diets were supplemented with 0, 50, 100, 200, 400, or 800 ppm Zn as Zn-proteinate (as-fed basis) or 2,000 ppm Zn as ZnO (as-fed basis). For the 28-d Exp. 3, the Phase 2 basal diet was supplemented with 0, 200, or 400 ppm Zn as Zn-proteinate, or 2,000 ppm Zn as ZnO (as-fed basis). All diets were fed in meal form. In Exp. 1, 2, and 3, pigs were bled on d 14, 28, or 27, respectively, to determine plasma Zn and Cu concentrations. For all three experiments, there were no overall treatment differences in ADG, ADFI, or G:F (P = 0.15, 0.22, and 0.45, respectively). However, during wk 1 of Exp. 1, pigs fed 2,000 ppm Zn as ZnO had greater (P 
0.05) ADG and G:F than pigs fed the basal diet. In all experiments, pigs fed a diet containing 2,000 ppm Zn as ZnO had higher plasma Zn concentrations (P < 0.10) than pigs fed the basal diet. In Exp. 1 and 3, pigs fed 2,000 ppm Zn as ZnO had higher fecal Zn concentrations (P < 0.01) than pigs fed the other dietary Zn treatments. In conclusion, organic Zn either as a polysaccharide or a proteinate had no effect on growth performance at lower inclusion rates; however, feeding lower concentrations of organic Zn greatly decreased the amount of Zn excreted.
Key Words: Excretion • Nursery Pigs • Organic Zinc • Performance • Plasma
Introduction
Poulsen (1995)
reported that feeding high concentrations of supplemental Zn (2,500 or 4,000 ppm Zn as ZnO) to nursery pigs decreased the incidence of postweaning scours. Other studies have shown a positive response to Zn in postweaning pig growth performance (Hahn and Baker, 1993; Hill et al, 2000). Hill et al. (2001) found that nursery pig growth response to ZnO reached a plateau at dietary concentrations of 1,500 to 2,000 mg Zn/kg. The use of high dietary Zn concentration has resulted in an environmental concern due to the high amount of Zn that is excreted in the feces. Studies have been conducted to evaluate the bioavailability and growth performance of nursery pigs fed inorganic Zn. In pigs, the bioavailability of Zn was lowest for ZnO and intermediate for Zn-lysine and Zn-methionine, when compared with Zn sulfate (Schell and Kornegay, 1996). Case and Carlson (2002) reported that pigs fed 500 ppm Zn as an organic Zn-polysaccharide complex had similar growth performance but excreted less Zn in the feces than pigs fed 3,000 ppm Zn as ZnO. The objective of this research was to evaluate lower concentrations of organic Zn-polysaccharide and Zn-proteinate complexes compared with ZnO during the nursery phase to determine whether they would maintain or improve growth performance and reduce fecal Zn concentration.
Materials and Methods
The research was approved by the Animal Care and Use Committee of the University of Missouri–Columbia before initiation of experiments.
Experiment 1
In Exp. 1, 306 pigs (PIC: C22 x TF4; average 17 ± 2 d of age and 5.14 ± 0.11 kg) were blocked based on initial weight, sex, and ancestry and randomly allotted to one of six dietary treatments for a 42-d study. Pigs were housed in an environmentally regulated building with slatted flooring over a pit. Each pen (1.2 x 1.2 m) had a stainless steel cup drinker and one stainless steel self-feeder. There were three pigs per pen, utilizing 102 pens with 17 replications per treatment.
Six dietary treatments were created by supplementation of the Phase 1 (d 1 to 14) basal diet (Table 1) containing 165 ppm Zn as ZnSO4 with 0, 125, 250, 375, or 500 ppm Zn (as-fed basis) as Zn-polysaccharide complex (Quali Tech, Chaska, MN), or 2,000 ppm Zn (as-fed basis) as ZnO (guaranteed minimum of 72% Zn). The dietary treatments were only fed during Phase 1 of the experiment, with all pigs fed a common Phase 2 (d 15 to 28) and Phase 3 (d 29 to 42) diet. The Phase 2 and 3 diets contained 165 ppm Zn as ZnSO4 and 16.5 ppm Cu as CuSO4 that was supplied by the basal premix. Sea-Questra Min Zinc (or SQM-Zn, guaranteed minimum of 22% Zn) is a metal-polysaccharide complex that is described by AAFCO (2002) as a product resulting from the complexing of a soluble salt with a polysaccharide solution.
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requirement estimates for the nursery pig (Table 1
).
Experiment 2
In Exp. 2, 98 pigs (PIC: C22 x TF4; average 17 ± 2 d of age and 5.27 ± 0.07 kg) were blocked based on initial weight, sex, and ancestry and randomly allotted to one of seven dietary treatments for a 28-d study. Pigs were housed in an environmentally regulated building equipped with plastic pen dividers and woven wire flooring over a flush system. Each pen (0.6 x 1.2 m) had a one-hole stainless steel self-feeder and one stainless steel nipple waterer. There were two pigs per pen, with 49 pens and seven replications per treatment.
Seven dietary treatments were created using a two-phase 28-d feeding program, with the basal diets containing 165 ppm Zn (as-fed basis) as ZnSO4 supplemented with 0, 50, 100, 200, 400, or 800 ppm Zn (as-fed basis) as Zn-proteinate (Zn-Prot; Bioplex Zn; Alltech Inc., Nicholasville, KY) or 2,000 ppm Zn as ZnO (guaranteed minimum of 72% Zn). The dietary treatments were fed during Phase 1 (d 1 to 14) and Phase 2 (d 15 to 28) of the experiment. Bioplex Zn (guaranteed minimum of 20% Zn) is a metal proteinate that is described by AAFCO (2002) as a product resulting from the chelation of a soluble salt with amino acids and/or partially hydrolyzed protein. All feed management and criteria collected were as described in Exp. 1.
Experiment 3
In Exp. 3, 20 barrows (GenetiPorc) averaging 17 ± 1 d of age were weaned and fed the basal Phase 1 diet (Table 1) during the 14-d adjustment period. After adjustment, barrows were blocked based on weight (11.21 ± 0.05 kg) and ancestry and randomly allotted to one of four dietary treatments for a 28-d study. Pigs were housed in an environmentally regulated building that had 20 individual stainless steel metabolism pens (0.6 x 1.2 m) equipped with a one-hole stainless steel self-feeder and a stainless steel nipple waterer. One pig was placed in each pen with five replications per treatment.
The four dietary treatments were created by supplementation of the Phase 2 basal diet (Table 1) containing 165 ppm Zn (as-fed basis) as ZnSO4 with 0, 200, or 400 ppm Zn (as-fed basis) as Zn-proteinate (Bioplex Zn, Alltech Inc.), or 2,000 ppm Zn (as-fed basis) as ZnO (72% Zn). Pigs were fed the dietary treatments during Phase 2 (d 1 to 28 of the experiment) to appetite twice daily. All other feed management and criteria collected were as described in Exp. 1.
Plasma Analysis
On d 14 (Exp. 1), 28 (Exp. 2), or 27 (Exp. 3), individual blood samples were collected from the anterior vena cava into 10-mL sodium-heparinized Vacutainer tubes (143 units of sodium heparin per tube) and placed on ice. Blood samples were centrifuged (Beckman GPR) within 1 hr at 3,000 x g for 10 min at 5°C. The separated plasma was stored at –20°C in 5-mL polypropylene tubes until mineral analysis could be performed. Ionized plasma samples were deproteinated with 10% trichloroacetic acid and supernatant was read on a flame atomic absorption spectrophotometer (SpectrAA-40 "Zeeman"; Varian Techtron, Mulgrave, Australia).
Fecal and Urine Analysis
In Exp. 1, fecal grab samples were collected twice daily (d 14, end of Phase 1 and d 28, end of Phase 2) and pooled before analysis of Zn and Cu concentrations. Fecal samples were not collected on d 42 at the end of Phase 3. In Exp. 3, fecal grab samples (approximately 100 g) and total urine collections were conducted twice daily (starting at 0800 and 1530) from d 22 to 26 of the study. All fecal samples were stored in sealed plastic bags at –20°C. Chromic oxide (Cr2O3) was added to all diets at 0.05% as an indigestible indicator. Urine volume was recorded and a 10% aliquot was saved in 1-L screw-cap polypropylene bottles. All urine collection pails and pens were washed after each collection, and 40 mL of 6 N HCl was added to each urine collection pail. All samples were stored at –20°C before processing for mineral analysis.
After thawing, fecal samples for individual pigs were pooled, mixed, and dried in a convection oven (Model 845; GCA Corp., Chicago, IL) at 55°C for 48 h. The dried fecal samples were ground to pass a 1-mm screen in a stainless steel Wiley mill. Thawed urine samples were pooled for individual pigs and two 800-mL aliquots were saved for mineral analysis. Fecal, feed, and urine samples were digested using a nitric-perchloric acid wet digestion (AOAC, 1990) of 4 mL of 10 M perchloric acid and 20 mL of 10 M nitric acid. Digested fecal, feed, and urine samples were diluted to the desired concentration with a mixture of 2.0% nitric acid and 3.0% perchloric acid and mineral concentrations were determined by flame atomic absorption spectrophotometer (SpectrAA-40 "Zeeman"; Varian Techtron).
All glassware used in the study was washed in 3.0% nitric acid and rinsed with deionized distilled water. Bovine liver standard (1577b; National Institute of Standards and Technology [NIST], Gaithersburg, MD) was used to determine accuracy of the results. Variation was accepted within the specified limits of NIST. Mineral concentrations were calculated from standard curves.
Statistical Analysis
Data were analyzed by ANOVA as a randomized complete block design using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC). Orthogonal contrasts were used to test for linear and quadratic effects of organic Zn additions (SQM-Zn or Zn-Prot). Planned nonorthogonal single-df comparisons made were the ZnO vs. the basal diet, and the ZnO diet vs. organic Zn treatments. Pen was used as the experimental unit for all data in Exp. 1 and 2. Individual pigs were the experimental unit in Exp. 3. An alpha level of 0.05 was used for determination of statistical significance of differences among treatments, with trends reported at 0.06 < P < 0.10.
Results and Discussion
Experiment 1
The addition of SQM-Zn in the Phase 1 diet had no effect on ADG, ADFI, or G:F (P = 0.12, 0.16, and 0.38, respectively) during the 42-d study (Table 2). There was a quadratic response (P = 0.05) to the addition of SQM-Zn from 0 to 500 ppm Zn, with the greatest ADG observed in the pigs fed 125 ppm Zn. During wk 1 of Exp. 1, pigs fed 2,000 ppm Zn as ZnO had greater ADG and G:F (P = 0.05 and 0.04, respectively) than pigs fed the basal diet containing 165 ppm Zn as ZnSO4. During Phase 1 and overall (d 1 to 42), ADG was greater (P < 0.10) for pigs fed 2,000 ppm Zn as ZnO than for pigs fed the basal diet. The body weight at the end of the treatment imposition (d 14) and final body weight (d 42) were also greater (P = 0.05 and 0.03, respectively) for pigs fed ZnO than for pigs fed the basal diet. In addition, pigs fed 2,000 ppm ZnO had greater (P = 0.03) ADFI than pigs fed any of the SQM-Zn treatments during wk 1. The SQM-Zn results in the present experiment differ from the results reported by Case and Carlson (2002), in which pigs fed 500 ppm Zn as SQM-Zn or 3,000 ppm Zn as ZnO had greater ADG than the other dietary treatments throughout a 28-d study. This could possibly be due to the health status of the pigs at weaning and the use of a different genetic source.
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). Plasma Zn concentrations did not differ between pigs fed 0, 125, 250, 375, or 500 ppm Zn as SQM-Zn. Plasma Cu concentrations were not affected by dietary treatment during the first 2 wk postweaning. All plasma Zn concentrations fell within the normal range of 0.5 to 1.5 mg/L Zn (Kaneko, 1989). Hahn and Baker (1993) reported a positive relationship between plasma Zn and ADG when plasma Zn concentrations were greater than 1.5 or less than 3.0 mg/L, although plasma Zn concentrations in this study were below 1.0 mg/L and the data would tend to support a positive relationship with ADG as previously observed in pigs fed ZnO. Carlson et al. (1999) found that pigs fed diets with adequate Zn through the nursery phase had an average plasma Zn concentration of 0.63 mg/L in the early-weaned pigs and 0.48 mg/L in traditionally weaned pigs.
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). There was a linear increase (P < 0.001) in daily Zn intake and fecal Zn concentration with increasing additions of SQM-Zn. Percentages of Zn excretion increased linearly (P 0.05) and percentages of Zn absorption decreased linearly (P 0.05) as the dietary concentration of SQM-Zn fed to pigs increased from 0 to 500 ppm Zn.
During Phase 2, the daily Zn intake and fecal Zn concentration (milligrams per day or percentage) were not affected by dietary treatments fed during Phase 1 (Table 3). However, pigs fed 2,000 ppm Zn as ZnO during Phase 1 had higher Zn absorption (milligrams per day and percentage) than pigs fed the basal diet (P = 0.02 and 0.01, respectively). Percentages of fecal Zn excretion were higher (P = 0.01) for pigs fed the basal diet than for pigs fed the ZnO diet. Pigs fed 2,000 ppm Zn as ZnO during Phase 1 had lower Zn absorption (milligrams per day) than pigs fed the SQM-Zn treatments in Phase 2 (P = 0.04). In addition, there was a trend for lower Zn absorption (percentage) during Phase 2 of pigs fed 2,000 ppm Zn as ZnO than pigs fed the SQM-Zn treatments during Phase 1.
During Phase 1, pigs fed 2,000 ppm Zn as ZnO had lower Cu absorption (milligrams per day) compared with pigs fed either the basal diet containing 165 ppm Zn as ZnSO4 or any SQM-Zn treatments (P = 0.04 and 0.05, respectively). During Phase 2, daily Cu (milligrams per day) intake, absorption, and fecal excretion were not affected by the addition of dietary Zn in Phase 1. However, there was a trend for lower percentage of Cu absorption during Phase 2 of pigs fed 2,000 ppm Zn as ZnO than pigs fed the basal diet during Phase 1.
Hill et al. (2002) reported no differences in ADG, ADFI, or G:F but they observed that pigs fed 2,000 ppm Zn as ZnO excreted 14 times more Zn in the feces than pigs that were fed 150 ppm Zn as ZnO. Case and Carlson (2002) reported that pigs fed 3,000 ppm Zn as ZnO excreted significantly more Zn than those receiving 500 ppm Zn as ZnO, 500 ppm Zn as Zn–amino acid complex, and 500 ppm Zn as Zn-polysaccharide, which all had similar fecal Zn concentrations. Case and Carlson (2002) observed the lowest fecal Zn concentrations in pigs receiving 150 ppm Zn as ZnO, thus supporting the findings in the present study that fecal Zn concentrations are reflective of the dietary Zn concentration fed to weanling pigs during the nursery phase.
Experiment 2
Similar to the results found in Exp. 1, weanling pigs fed Zn-proteinate complex had no effect on overall ADG, ADFI, or G:F (P = 0.18, 0.28, and 0.53, respectively) through the entire 28-d study (Table 4). However, during Phase 1 (d 1 to 14), pigs fed 2,000 ppm Zn as ZnO had higher ADFI (P = 0.02) and a trend for higher ADG (P < 0.10) than pigs fed the basal diet containing 165 ppm Zn as ZnSO4. Heavier final body weights (P < 0.10) were observed in pigs fed 2,000 ppm Zn as ZnO compared with pigs fed the basal diet containing 165 ppm Zn as ZnSO4. In addition, during Phase 1, pigs fed ZnO had higher ADFI (P = 0.04) than pigs fed any of the diets supplemented with Zn-Prot (50, 100, 200, 400, or 800 ppm Zn). On d 28, pigs fed ZnO had higher plasma Zn concentrations than pigs fed the basal diet (P = 0.01).
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, in which the growth performance response to ZnO reached a plateau around 1,500 to 2,000 mg Zn/kg and was independent of the inclusion of an antibacterial agent, such as carbadox. However, other experiments have found no growth improvement in pigs fed high concentrations of Zn as ZnO. Schell and Kornegay (1996) found no growth enhancement when nursery pigs were fed pharmacological concentrations of inorganic Zn after weaning, although serum and tissue Zn concentrations were increased. Mavromichalis et al. (2000) reported that feeding ZnO with high (93%) or low (39%) bioavailabilities did not affect growth rate in nursery pigs during a 21-d study. Therefore, a possible explanation for observing no improvement in growth performance in our experiments could be due to the health status of pigs, the feeding duration, and/or dietary phase in which experimental treatments of supplemental zinc were fed.
Experiment 3
Pigs fed 2,000 ppm Zn as ZnO had greater final body weights (P = 0.03) and overall (d 1 to 28) ADG and ADFI compared with pigs fed 200 or 400 ppm Zn as Zn-Prot (P = 0.03, 0.02, and 0.002, respectively; Table 5). There was a trend for pigs fed 2,000 ppm Zn as ZnO to have higher overall ADFI (P < 0.10) than pigs fed the basal diet containing 165 ppm Zn as ZnSO4. On d 1, there were no treatment differences in plasma Cu and Zn concentrations with means of 1.5 and 1.1 mg/L, respectively (data not shown). On d 27, plasma Zn concentration (milligrams per liter) tended to be higher (P < 0.10) for pigs fed ZnO compared with pigs fed the basal diet (Table 5). Plasma Cu concentrations were not different between pigs fed the dietary treatments on d 27 of the experiment. The plasma Zn and Cu concentrations were slightly higher than plasma concentrations observed in Exp. 1 and 2. This could possibly be due to the difference in collection time (d 14 vs. 28) relative to the duration of feeding dietary treatments. In addition, in Exp. 3, there were differences in the age (14 d older) and weight (6 kg heavier) of pigs at the initiation of the study than in Exp. 1 and 2, resulting in an overall greater ADFI.
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). However, for pigs fed Zn-Prot, there were greater concentrations (P < 0.01) in the milligrams of daily Zn intake and daily fecal Zn excreted than pigs fed the basal diet. Percentages of Zn absorbed and retained increased (P < 0.02) when pigs were fed increasing dietary Zn-Prot concentration (200 vs. 400 ppm Zn-Prot). In addition, pigs fed 400 ppm Zn as Zn-Prot had greater daily Zn intake and daily fecal Zn excreted (P < 0.03 and 0.05, respectively) than pigs fed 200 ppm Zn as Zn-Prot. Hoover et al. (1997) previously reported that pigs fed 3,000 ppm Zn as ZnO excreted more Zn in feces and urine than pigs fed the basal diet. The results from this experiment indicate that elevated dietary Zn concentrations above 400 ppm increased Zn absorption and retention. Poulsen and Larsen (1994) also reported that the Zn retention of growing pigs increased as supplemental dietary ZnO increased up to 0.30 g/d.
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0.001) amounts of Cu intake, Cu absorbed, Cu retained, and Cu excreted in feces (milligrams per day) compared with pigs fed the basal diet or the Zn-Prot diets (Table 6). Percentages of Cu absorbed and retained were higher (P 0.02) for pigs fed ZnO than for pigs fed the basal diet or the Zn-Prot diets. Copper intake (milligrams per day) was higher (P = 0.04) for pigs fed the Zn-Prot diets than pigs fed the basal diet. In addition, pigs fed the Zn-Prot diets (200 or 400 ppm) had greater Cu absorption and retention (milligrams per day or percentage) than pigs fed the basal diet. Urinary Cu excretion (milligrams per day and percentage) was not affected by dietary Zn treatment. O’Dell (1989) reported that a high dietary intake of Zn can reduce the copper status of rodents, pigs, sheep, cattle and poultry. However, in the present study, Cu absorption and retention increased when pigs were fed dietary Zn concentrations above their requirement. This could possibly be due to the higher amount of Cu present in the ZnO and organic trace mineral sources. Implications
This study suggests that Zn supplementation above the 165 ppm Zn (as-fed basis) provided as ZnSO4 in the basal diets using organic Zn sources does not improve growth performance. Feeding 2,000 ppm Zn (as-fed basis) as ZnO improved the growth performance of pigs weaned at approximately 17 d of age. The quantity of Zn excreted in the feces by pigs was directly related to the dietary Zn concentration, regardless of the Zn source. Pigs fed 2,000 ppm Zn (as-fed basis) as Zn oxide excreted approximately 10 times more Zn in the feces than the pigs fed the basal diet containing 165 ppm Zn (as-fed basis) as ZnSO4. Therefore, feeding lower concentrations of organic Zn sources in nursery pig diets as replacements for pharmacological concentrations (2,000 ppm, as-fed basis) of inorganic Zn as Zn oxide would decrease the concentration of Zn excretion. Nonetheless, the lowest concentration of Zn excretion would result when no supplemental dietary Zn is fed to nursery pigs above their nutrient requirement.
Footnotes
1 The Missouri Agric. Exp. Stn. supported this project. Appreciation is expressed to Quali Tech Inc. and Alltech Inc. for providing the organic trace minerals used in these experiments. 
2 Correspondence: S133 Animal Sciences Center (phone: 573-882-7859; fax: 573-884-4545; e-mail: carlsonm{at}missouri.edu).
Received for publication April 8, 2003. Accepted for publication January 29, 2004.
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