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Effect of dietary trace mineral concentration and source (inorganic vs. chelated) on performance, mineral status, and fecal mineral excretion in pigs from weaning through finishing^1,2

B. L. Creech^*, J. W. Spears^*,3, W. L. Flowers^*, G. M. Hill, K. E. Lloyd^*, T. A. Armstrong^*,4 and T. E. Engle^*,5

^* Department of Animal Science, North Carolina State University, Raleigh 27695-7621; and and Department of Animal Science, Michigan State University, East Lansing 48824-1225

	Abstract

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Two hundred and sixteen weanling gilts (6.65 ± 0.08 kg) were used to determine the effects of decreasing supplemental concentrations of Zn, Cu, Fe, and Mn, and trace mineral source (inorganic vs. chelated) on growth performance, mineral status, and fecal mineral concentrations from weaning through development. The study was conducted over three trials with 72 pigs in each trial. Gilts were blocked by weight and randomly assigned to either 1) control, 2) reduced inorganic, or 3) reduced chelated trace minerals. The control diet was supplemented with 25, 150, 180, and 60 mg/kg of Cu, Zn, Fe, and Mn (in sulfate forms), respectively, during the nursery phase and 15, 100, 100, and 40 mg/kg of supplemental Cu, Zn, Fe, and Mn, respectively, during the growing and gilt-developer phases. Reduced inorganic and reduced chelated treatments were supplemented during all phases with 5, 25, 25, and 10 mg/kg of Cu, Zn, Fe, and Mn, respectively. The reduced chelated treatment supplied 50% of the supplemental Cu, Zn, Fe, and Mn in the form of metal proteinates, with the remainder from sulfate forms. Performance by control pigs did not differ from pigs fed the reduced trace mineral treatments during the nursery and grower-development periods. Gain:feed was lower (P < 0.05) for pigs fed the reduced inorganic compared with those fed the reduced chelated treatment during the nursery period. Trace mineral source did not affect performance during the growing or gilt-developer phase. Plasma Zn concentration and alkaline phosphatase activity were higher (P < 0.01) in control pigs than in those receiving reduced trace minerals during the nursery and growing phases. Plasma Cu concentration and ceruloplasmin activity were generally not affected by treatment. Hemoglobin concentrations were lower (P < 0.05) for the reduced inorganic compared with the reduced chelated treatment in the nursery phase. Fecal concentrations of Cu, Zn, and Mn were lower (P < 0.05) in pigs fed reduced trace minerals than in controls during all production phases. Fecal Zn concentration during the nursery and fecal Cu concentrations during the growing and gilt-developer phases were lower (P < 0.05) in pigs fed the reduced chelated compared with the reduced inorganic treatment. Results indicate that reducing the concentrations of Zn, Cu, Mn, and Fe typically supplemented to pig diets will greatly decrease fecal mineral excretion without negatively affecting pig performance from weaning through development.

Key Words: Copper • Pigs • Zinc

	Introduction

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Long-term application of swine lagoon effluent (Mueller et al., 1994) and broiler litter (Kingery et al., 1994) has resulted in increased soil concentrations of Zn and Cu. Zinc and/or Cu accumulation in soil has been implicated to reduced crop yields (Tucker, 1997; Matsui and Yano, 1998).

A common practice within the swine industry is to formulate diets with trace mineral concentrations that exceed NRC (1998) recommendations. When trace minerals are fed in excess of animal requirements, more is excreted in waste because of homeostatic mechanisms that serve to regulate tissue concentrations of minerals (Spears, 1996). Formulation of diets with mineral concentrations close to requirements would seem to be an appropriate means of reducing concentrations of Zn and Cu in waste without affecting animal performance.

The balance among minerals, in regard to dietary concentrations relative to animal requirements, is an important factor affecting mineral utilization. Antagonistic interactions can occur between Fe and Mn and between Fe and Cu and Zn (O’Dell, 1997). Therefore, reducing dietary Fe and Mn concentrations to levels more in line with requirements may serve to minimize Zn and Cu requirements. Another strategy for reducing trace mineral concentrations in diets is inclusion of mineral sources that may exhibit greater bioavailability than commonly used inorganic forms. Results have been variable, but some studies have indicated that chelated forms of trace minerals are more bioavailable than inorganic forms (Spears, 1996).

The current study was conducted to determine the effects of reducing supplemental concentrations of Zn, Cu, Fe, and Mn on growth performance, mineral status, and fecal mineral concentrations of gilts from weaning through growing and development. A second objective was to determine whether replacing 50% of the supplemental Zn, Cu, Fe, and Mn with chelated forms would improve performance and/or decrease fecal mineral excretion.

	Materials and Methods

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Experimental Design
Experimental procedures involving animals were approved by the North Carolina State University Animal Care and Use Committee. Two hundred and sixteen weanling crossbred gilts (6.65 ± 0.08 kg), 18 to 21 d of age, were used in three trials (n = 72 gilts per trial). The experimental design was similar for all trials. The gilts were blocked by weight and randomly assigned within a weight block to one of three treatments. Treatments consisted of 1) a control, 2) reduced inorganic trace minerals, or 3) reduced chelated trace minerals. Supplemental trace mineral concentrations in the control diets were formulated to be typical of those currently used in the swine industry. The control treatment during the nursery phase contained 25, 150, 180, and 60 mg/kg of supplemental Cu, Zn, Fe, and Mn, respectively. During the growing and finishing phase, supplemental levels were reduced to 15, 100, 100, and 40 mg/kg for Cu, Zn, Fe, and Mn, respectively. The reduced inorganic and reduced chelated treatments were supplemented during all production phases with 5, 25, 25, and 10 mg/kg of supplemental Cu, Zn, Fe, and Mn, respectively. Iron and Mn were decreased in the reduced inorganic and reduced chelated treatments because they are commonly supplemented in excess of NRC (1998) recommendations, and because high dietary concentrations of these two minerals may increase Zn and/or Cu requirements. The control and reduced inorganic treatments supplied 100% of the supplemental Cu, Zn, Fe, and Mn from inorganic sulfate forms. The reduced chelated treatment supplied 50% of the supplemental Cu, Zn, Fe, and Mn in the form of metal proteinates (Chelated Minerals Corp., Salt Lake City, UT), with the remainder being supplied from inorganic sulfate forms.

Nursery Phase
Pigs were housed six pigs per pen (four replicate pens per treatment per trial) in an environmentally controlled nursery. The temperature in the nursery was 30°C for the first week and was lowered by 1°C each subsequent week. Ingredient composition of the nursery diets is shown in Table 1. A complex diet was fed from d 1 to 14. A corn-soybean meal based diet was fed from d 15 to 41. Diets were formulated to meet or exceed NRC (1998) requirements. Analyzed trace mineral concentrations in diets are shown in Table 2. Feed and water were provided ad libitum. Feed weighbacks were taken weekly. Body weights were obtained on d 0, 14, and 41 of the study.

Sample Collections and Analytical Procedures
Blood was collected on d 28 of the nursery phase from three randomly selected pigs per replicate pen in each trial. Two randomly selected pigs per replicate pen were bled on d 41 and 54 of the growing and gilt-developer phases, respectively. Samples were obtained via jugular venipuncture into heparinized tubes designed for trace mineral analysis (Vacutainer 9735, Becton, Dickinson, and Co., Rutherford, NJ). A sample of whole blood was retained for hemoglobin determination. Plasma, obtained after centrifugation at 2,500 x g for 20 min, was frozen and later analyzed for Cu and Zn concentration, and alkaline phosphatase (AP) and ceruloplasmin activity.

Fecal grab samples were obtained by rectal palpation from 12 pigs per treatment (three randomly selected pigs per pen) in Trial 3 of the nursery phase for fecal mineral analysis. Samples were taken from the same pigs on d 38 at 0800, d 39 at 1500, and d 40 at 2100. Fecal samples (two pigs per pen) were taken on d 33, 34, and 35 of the growing phase, and on d 56, 57, and 58 of the gilt-developer phase at the times specified for the nursery phase. Fecal samples were composited across times within a phase for Cu, Zn, Fe, and Mn analysis.

A 100-µL sample of whole blood was used for total hemoglobin determination via the cyanomethemoglobin method (Sigma Chemical Co., 1995). Plasma was diluted 1:3 (vol/vol) with deionized water and analyzed for Cu and Zn concentration via flame atomic absorption spectrophotometry (model 5000, Perkin Elmer, Norwalk, CT). Plasma ceruloplasmin activity was determined by the method described by Houchin (1958), with results expressed as absorbance units. Plasma AP activity was determined using the method described by Sigma Chemical Co. (1987).

Feed and fecal samples were dried and ground to pass a 1-mm screen. Feed samples were taken at every mixing from several bags per treatment. Samples were then dried at 55°C for at least 48 h. Feed samples were then ground, mixed evenly, and composited by treatment for the respective phase. Fecal samples were also composited by pen following drying and grinding.

Feed and fecal samples were prepared for mineral analysis by wet ashing using a microwave digestion system (model MDS-81D, CEM Corp., Matthews, NC). Approximately 0.5 g of sample (DM basis) was weighed in duplicate and placed in teflon-lined digestion vessels. Ten milliliters of trace mineral grade nitric acid was added to the samples. Samples were digested for 30 min at room temperature and then sealed. The vessels were placed in the microwave for 5 min at 50% power, 15 min at 70% power, and 10 min at 0 power. They were then vented, and 2 mL of 30% hydrogen peroxide was added. Vessels were placed in the microwave for 3 min at 50% power and 2 min at 0 power. Ashed samples were then brought up to volume in 25-mL volumetric flasks and analyzed for Cu, Zn, Fe, and Mn via flame atomic absorption spectrophotometry.

Statistical Analyses
Data were analyzed using the GLM procedures of SAS. The model included treatment, trial, block, and trial x treatment interaction. When the trial by treatment interaction was significant, data were analyzed by trial. When the trial x treatment interaction was not significant (P > 0.10), only combined means are presented. Pen was used as the experimental unit for all variables. Single-df contrasts were used to compare 1) control vs. the two reduced treatments and; 2) reduced inorganic vs. reduced chelated treatment.

	Results

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Performance
Gain and ADFI were not affected by treatment during the first 14 d of the nursery period when pigs were fed a complex diet (Table 4). Gain:feed tended (P < 0.10) to be higher for control pigs compared with those fed reduced trace mineral diets during this period. However, ADG, ADFI, and G:F of control pigs did not differ from those fed reduced trace minerals from d 15 to 41 or over the entire 41-d nursery period. Gain:feed was higher (P < 0.05) in pigs fed the reduced chelated diet from d 15 to 41 and over the total nursery period compared with pigs fed the reduced inorganic diet. The improved G:F in pigs fed the reduced chelated diet was due to feed intake being numerically lower (P = 0.16) in this group compared with pigs in the reduced inorganic treatment.

Plasma Zn concentration in the gilt-developer phase (d 54) was affected by a treatment x trial interaction (P < 0.01; Table 6). Pigs fed the reduced trace mineral treatments had lower (P < 0.05) plasma Zn concentrations than control pigs in Trial 3, but not in Trials 1 and 2. Plasma AP activity was not affected by trace mineral level or source. During the gilt-developer phase, plasma Cu was also affected by a treatment x trial interaction (P < 0.05). In Trial 1, control pigs had higher (P < 0.05) plasma Cu concentrations than those fed the reduced trace mineral diets. Plasma Cu was higher (P < 0.05) in the reduced chelated treatment compared with the reduced inorganic treatment in Trial 2. In Trial 3, plasma Cu was not affected by treatment. Ceruloplasmin activity and hemoglobin concentration were not affected by treatment during the gilt-developer phase.

Fecal Mineral Concentrations
Copper concentrations in fecal samples obtained during the nursery, growing, and gilt-developer phases were higher (P < 0.01) for control pigs than for those fed reduced Cu diets (Table 7). Pigs fed the reduced inorganic diet had higher (P < 0.01) fecal Cu concentrations than pigs fed the reduced chelated diet during the growing phase. Fecal Cu was affected by a treatment x trial interaction (P < 0.01) in the gilt-developer period. Control pigs had higher (P < 0.01) fecal Cu concentration than pigs fed the reduced trace mineral treatments in all three trials. Copper concentrations in feces were lower in pigs fed the reduced chelated diet compared with those fed the reduced inorganic diet in Trials 2 (P < 0.01) and 3 (P < 0.05), but not in Trial 1.

Pigs fed the reduced chelated diet had lower fecal Fe (P < 0.10) and Mn (P < 0.05) concentrations than pigs fed the reduced inorganic diet during the nursery phase (Table 7). Fecal Mn concentrations were higher (P < 0.05) at all sampling times in controls compared with pigs fed reduced trace minerals. Control pigs had higher (P < 0.01) fecal Fe concentrations than did those fed the reduced trace mineral diets during the growing and gilt-developer phases.

	Discussion

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Reducing the amounts of Zn, Cu, Fe, and Mn supplemented to diets in the current study did not adversely affect performance of gilts from weaning through development. Based on NRC (1998) recommendations and analyzed mineral concentrations in the reduced trace mineral diets (Table 3), Zn was most likely to be limiting. The Phase I nursery diet analyzed slightly lower in Zn than the 100 mg Zn/kg recommended by NRC (1998) for pigs weighing 5 to 10 kg. By analysis, growing and gilt-developer diets contained approximately 150% of current NRC (1998) recommended requirements for Zn. Based on basal levels of Zn in previous studies with corn-soybean meal-based diets, the growing and gilt-developer diets were higher in Zn than anticipated, considering that only 25 mg Zn/kg was supplemented to the reduced diets (Pond and Jones, 1964; Hill and Miller, 1983; Wedekind et al., 1994).

Previous studies indicate that Zn requirements of growing and finishing pigs, based on growth, do not exceed 50 mg/kg diet. Addition of Zn (50 or 500 mg Zn/kg diet) to a corn-soybean meal-based diet containing 35 mg Zn/kg did not affect performance of growing and finishing pigs (Hill and Miller, 1983). The addition of Zn to a corn-soybean meal-based diet containing 23 to 27 mg of Zn/kg also did not improve performance of pigs during the nursery or growing phase (Hill et al., 1986). However, Zn supplementation of the control diet did increase gain and feed intake during the finishing phase of this study (Hill et al., 1986). Average daily gain and feed intake were higher in gilts fed diets containing 53 or 80 mg of Zn/kg compared with those fed 22 mg of Zn/kg (Liptrap et al., 1970). Wedekind et al. (1994) depleted Zn stores of pigs during the nursery phase by feeding diets containing 37 to 42 mg of Zn/kg. Zinc was then supplemented at 0, 5, 10, 20, 40, and 80 mg/kg in Exp. 1, and at 0, 7.5, and 15 mg/kg in Exp. 2 during the growing and finishing phases. The control growing and finishing diets used in this study contained 32 and 27 mg of Zn/kg, respectively. Supplementation of the control diets with Zn increased plasma and bone Zn, but did not affect pig performance in either experiment.

In the current study, even though performance of pigs was not affected by treatment, plasma Zn and AP activity were lower in pigs fed reduced dietary Zn. Alkaline phosphatase activity and serum or plasma Zn have been used as indicators of Zn status. However, the level of circulating Zn in pigs necessary to maximize Zn dependent functions has not been defined. Gilts fed diets containing 48 and 70 mg of Zn/kg had higher serum AP activity and serum Zn concentrations than those fed 29 mg of Zn/kg (Liptrap et al., 1970). Average daily gain and ADFI were also lower in pigs fed the low Zn diet (Liptrap et al., 1970). In agreement with the current study, Wedekind et al. (1994) observed that Zn supplementation of diets containing 27 to 32 mg of Zn/kg increased plasma Zn without affecting pig performance.

Bioavailability of Zn may be limited by high dietary Ca. When Ca levels are increased in a diet with low dietary Zn, the incidence of parakeratosis is increased dramatically (Lewis et al., 1956; Luecke et al., 1956). In the current study, Ca was supplied in the diets at higher than NRC (1998) recommended requirements, but no cases of parakeratosis were observed even in pigs fed the reduced Zn diets. The nursery diets in the current study contained approximately 120% and the growing and gilt-developer diets contained 154 to 177% of the NRC (1998) Ca requirements.

Iron and Mn are commonly present in swine diets in excess of requirements. The reduced trace mineral diets were supplemented with lower concentrations of Fe and Mn to minimize any antagonistic effects of these minerals on Cu and Zn. Even in diets with reduced trace minerals added, total dietary (supplemental plus basal levels in the feedstuffs) Fe and Mn concentrations exceeded NRC (1998) recommendations by at least threefold (Table 3). Therefore, it is unlikely that either Fe or Mn limited biochemical functions dependent on these metals. Most commonly used feedstuffs are good sources of Fe. For example, commercial dicalcium phosphate or defluorinated phosphate contains approximately 10,000 mg Fe/kg (Spears, 1996). In pigs, Fe from defluorinated phosphate is at least 50% as available as Fe from ferrous sulfate (Kornegay, 1972). Svajgr et al. (1969) reported that practical corn-soybean meal-based diets contain adequate Mn to meet requirements of growing-finishing pigs.

The total Cu content of reduced trace mineral diets in the current study exceeded NRC recommendations in all phases of the study. Plasma Cu concentrations and ceruloplasmin activity observed in pigs suggest that the reduced-Cu diets provided adequate Cu. Dietary Cu requirements needed to maintain optimal metabolic functions in swine have received minimal attention. Hedges and Kornegay (1973) found that the Cu requirement was no greater than 7 mg/kg in nursery pigs fed high dietary Fe.

When minerals are supplemented in excess of the animal’s requirement, more is excreted due to decreased efficiency of utilization for that mineral (Spears, 1996). The current study clearly indicates that reducing dietary Zn and Cu to concentrations closer to nutritional requirements is an effective means of reducing excretion of Zn and Cu in swine waste. Fecal concentrations of Zn and Cu were reduced by approximately 50% in pigs fed reduced dietary Zn and Cu. Decreasing Zn and Cu in swine waste is important because accumulation of these minerals in soil can lead to toxicity in plants (Tucker, 1997; Matsui and Yano, 1998) and therefore potentially affect the sustainability of large swine operations.

In the nursery phase, pigs fed 50% of their supplemental Zn, Cu, Fe, and Mn from chelated metal proteinates gained more efficiently than those fed similar concentrations of trace minerals solely from inorganic sulfate forms. Veum et al. (1995) also reported that replacing a portion of the inorganic trace minerals with proteinate forms improved feed efficiency in nursery pigs. During the growing and gilt-developer phases, pig performance was similar in pigs fed the reduced chelated treatment and those fed the reduced inorganic treatment. However, fecal Cu and Zn concentrations were lower or at least tended to be lower in pigs fed the reduced chelated diet. Pigs fed proteinate forms of Zn and Cu had higher liver Zn and Cu concentrations than did pigs fed sulfate forms of these metals (Schiavon et al., 2000). This suggests a higher utilization of Zn and Cu from the proteinate compared with the sulfate sources.

	Implications

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The current study indicates that zinc and copper concentrations typically supplemented to gilt diets can be greatly decreased without affecting pig performance from weaning through development. Reducing supplemental concentrations of zinc and copper in pig diets decreased fecal concentrations of copper and zinc by approximately 50%. Lower excretion of zinc and copper by swine will help prevent accumulation of these metals in soils where swine waste is applied. Further studies are needed to better define nutritional requirements of pigs for zinc and copper.

	Footnotes

 
¹ Use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Service or criticism of similar products not mentioned.

² This research was supported by grants from the Animal Waste Six-State Consortium and the North Carolina State Univ. Animal and Poultry Waste Management Center, and by a gift from Chelated Minerals Corp., Salt Lake City, UT. Appreciation is extended to Akey, Lewisburg, OH, for supplying the vitamin premixes.

⁴ Present address: Elanco Animal Health, Cary, NC 27511-6614.

⁵ Present address: Dept. of Anim. Sci., Colorado State Univ., Fort Collins 80523-1171.

³ Correspondence—phone: 919-515-4008; fax: 919-515-4463; e-mail: Jerry_Spears{at}ncsu.edu.

Received for publication September 26, 2003. Accepted for publication March 22, 2004.

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