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METABOLISM AND NUTRITION |
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* Mineral Nutrition Research Division, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100094, China; State Key Laboratory of Animal Nutrition, Beijing 100094, China; and College of Life Science and Technology, Southwest University for Nationalities, Chengdu 610041, China
2 Corresponding author: wlysz{at}263.net
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: zinc • requirement • broiler
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The requirement of nutrients including Zn for animals is usually defined as the minimum dietary concentration required for maximum performance (Sterling et al., 2005). An animal’s maximum performance is difficult to assess because there are often several response criteria for each nutrient. There may be different maximum responses for the various criteria such as growth, feed efficiency, carcass composition, and bone ash, etc. The choice of responsive parameters to use in defining requirements is important. When a corn-soybean meal diet is used, the Zn in the basal diet (usually more than 40 mg/kg) often meets the requirement for chick growth, and there is no significant change in weight gain by Zn supplement (Wedekind et al., 1992). On the other hand, weight gain can be influenced by many factors and is not a sensitive criterion for Zn requirement estimation (Luo et al., 1991). So, weight gain can no longer be used as an index of Zn requirement when a corn-soybean meal diet is used, and criteria other than growth must be chosen to evaluate the Zn requirement. Tissue Zn accumulation and Zn-containing enzyme activities have been considered to be sensitive criteria, and some requirement values of Zn have been determined based on Zn accumulation in bone (Wedekind et al., 1992). Methodological advances to assess gene expression have provided a new spectrum of research tools to identify individual genes and groups of genes that produce normal and altered physiology. Quantitative, real-time, reverse transcription-PCR (QRT-PCR) provides a highly sensitive and reproducible method for measuring changes in expression of specific genes through transcript sequence detection. The emergence of this new molecular technique is especially promising for the development of a new generation of biomarkers. It has been suggested that Zn increases the synthesis and expression of metallothionein (MT), a cysteine-rich protein that acts as a free radical scavenger (Cousins and Lee-Ambrose, 1992; Sullivan et al., 1998). Similar results have been observed in the synthesis and expression of Zn transporter-2 (ZnT-2), which reduces intracellular cytoplasmic Zn by promoting Zn efflux from cells or into intracellular vesicles (Langmade et al., 2000; Liuzzi et al., 2001). Functions of Zn can be categorized as catalytic (metalloenzymes), structural (e.g., Zn finger domains of proteins), and regulatory (e.g., metal response elements of gene promoters; Cousins, 1996). Cousins et al. (2003) proposed that the catalytic and structural roles of Zn cannot serve as functional indicators; however, the regulatory role of Zn may provide a responsive indicator. Through an interaction with a metal-responsive transcription factor (MTF-1), Zn has been shown to regulate a number of genes in which MT and ZnT-2 are included (Lichtlen et al., 2001).
The current dietary Zn allowance for broilers was based on growth. Although effects of dietary Zn on the tissue Zn concentrations were assessed in previous Zn requirement studies, optimal dietary Zn levels for the activity of Zn-containing enzyme, tissue MT concentration, and expression of MT, ZnT-2 have not been studied. The objective of this study was to examine the effects of various dietary Zn levels on tissue Zn concentrations, Zn metalloenzyme activities (alkaline phosphatase, copper-zinc superoxide dismutase, and 5'-nucleotidase), MT concentration, MT mRNA level, and ZnT-2 mRNA level in practical diets of chicks. The results may help in choosing a suitable criterion to determine the optimal dietary Zn level of broilers more accurately.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A total of 384 one-day-old Arbor Acres (AA) male broiler (Huadu Broiler Breeding Corp., Beijing, China) chicks were used in the 21-d experiments. The birds were randomly allotted to 1 of 8 treatments for 6 replicate cages of 8 chicks each in a completely randomized design. Dietary treatments included the basal diet supplemented with 0, 20, 40, 60, 80, 100, 120, or 140 mg/kg added Zn from ZnSO4·7H2O.
The basal corn-soybean meal diet was formulated to meet or exceed the requirements for starter broilers (NRC, 1994) except for Zn and contained 28.37 mg of Zn/kg of diet on an as-fed basis, by analysis (Li et al., 2004; Table 1
). Chicks were maintained on a 24-h constant light schedule and allowed ad libitum access to experimental diets (Table 1) and tap water, which contained no detectable Zn. Birds were managed according to guidelines approved by Arbor Acres Farm in Beijing.
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Feed intake and BW per cage were recorded and corrected for mortality at the end of every week. At the end of the experiment, chicks were individually weighed, and 3 birds from each cage were selected according to the average BW of the cage. Blood samples were taken from each bird via cardiac puncture and then centrifuged to harvest serum for 5'-nucleotidase (5'-NT) activity analysis. Chicks were immediately killed by cervical dislocation. The pancreas and kidney were excised, a subsample was frozen (–20°C) for Zn and MT content analysis, and a second subsample was frozen in liquid nitrogen for assays of MT and ZnT-2 gene expression. Liver samples were obtained from the left lobe and frozen (–20°C) for copper-Zn superoxide dismutase (CuZnSOD) activity analysis. The right tibia was excised and frozen in an individual heat-sealed polyethylene bag for Zn analysis. Tibia bones were boiled for approximately 10 min in deionized water and all soft tissue was removed; then, the bones were dried for 12 h at 105°C and finally ashed in a muffle furnace at 550°C for 16 h. The samples of 3 individual chicks from each cage were pooled before analysis.
Zn Concentration
Zinc concentrations in diets, water, and tissues were determined by inductively coupled argon plasma spectroscopy (model 9000, Thermo Jarrell Ash, Waltham, MA) as described by Li et al. (2004). Validation of the mineral analysis was conducted using bovine liver powder [GBW (E) 080193, National Institute of Standards and Technology, Beijing, China] as a standard reference material.
Enzyme Activity
Activity of liver CuZnSOD was measured by the nitrite method as described by Oyanagui (1984). Serum 5'-NT activity was analyzed using a coupled-enzyme analysis kit (265 A, Sigma, St. Louis, MO) and automated spectro-photometric analyzer (Cobas FARA II; Roche, Palo Alto, CA), according to the manufacturer’s directions.
MT Concentration
The concentration of MT in pancreas was determined by 109Cd-hemoglobin affinity assay (Eaton and Toal, 1982) with a gamma spectrometer (model 4000, Beckman Instruments, Palo Alto, CA). The concentration of MT was calculated using a 109Cd-MT binding stoichiometry of 7:1.
Total RNA Isolation and Reverse Transcription
Total RNA in pancreas tissue was isolated using Trizol reagent (cat. no. 15596-026, Invitrogen Life Technologies) according to the manufacturer’s instructions. Concentrations of total RNA were estimated by measuring UV light absorbance at 260 nm (Ultrospec III, Perkin Elmer Cetus). Reverse transcription was performed using the SuperScript III first-strand synthesis system for RT-PCR (kit 12371-019, Invitrogen Life Technologies) and oligo(dT)20 as a primer.
Generation of cDNA for Real-Time PCR Calibration Curves
According to the sequence of the gene published in GenBank, primers for MT, ZnT-2, and β-actin gene (housekeeping gene) were chosen with Primer Express Software (Applied Biosystems Incorporation, Foster, CA). Two microliters of the reverse transcription product were amplified for 35 cycles in a 20-µL reaction system containing 10.0 µL of PCR reaction kit (Tianwie Corp., Beijing, China) and 0.5 mmol/L of each forward and reverse primer (Biological Engineer Corp., Shanghai, China). The amplification conditions for MT, ZnT-2, and β-actin gene were conducted using denaturation at 94°C for 1 min, annealing at 60°C for 30 s, and primer extension at 72°C for 30 s. After final extension at 72°C for 8 min, the integrity of the linear double-stranded cDNA was verified by ethidium bromide staining and plating on agarose gel. Primer sequences, the position in the coding region, and the expected PCR product length are summarized in Table 2. Ten-fold serial dilutions of MT, ZnT-2, and β-actin gene PCR products were prepared for real-time PCR calibration curves.
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The quantification of all gene transcripts was carried out by QRT-PCR analysis in the fluorescence detection system (7000HT, Applied Biosystems Incorporation) according to optimized PCR protocols and the SYBR Green qPCR kit (4309155, Applied Biosystems Incorporation), in which SYBR Green I was a double-stranded DNA-specific fluorescent dye. The PCR reaction system (25 µL) contained 12.5 µL of SYBR Green qPCR mix, l µL of forward primer (10 µmol/L), l µL of reverse primer (10 µmol/L), 1 µL of cDNA template, and 4.5 µL of water. For the PCR reaction, the following experimental run protocol was used: 10 initial denaturations (10 min at 95°C) and then a 2-step amplification program (15 s at 95°C followed by 1 min at 60°C) repeated 40 times. Real-time quantification was monitored by measuring the increase in fluorescence caused by the binding of SYBR Green dye to double-stranded DNA at the end of each amplification cycle. At the end of the PCR, dissociation was performed by slowly heating the samples from 60 to 95°C and continuous recording of the decrease in SYBR Green fluorescence resulting from the dissociation of double-stranded DNA. The threshold cycle (Ct), defined as the cycle at which an increase in fluorescence above a defined baseline can be first detected, was determined for each sample.
The relative standard curve methods were used for quantification of gene expression. The MT, ZnT-2, and β-actin gene mRNA levels were determined from the threshold cycle plotted on the respective standard curves. The results were expressed as the MT, mRNA/β-actin mRNA, ZnT-2 mRNA/β-actin mRNA ratio. Each PCR run included a blank reverse-transcribed cDNA and calibration curve dilution samples. Runs were performed in triplicate.
Statistical Analysis
Data were subjected to 1-way ANOVA using the GLM procedure of SAS (SAS Institute, 1996). Pen was the experimental unit. Orthogonal comparisons were applied for linear and quadratic responses of dependent variables to independent variables. In addition, nonlinear models (quadratic and asymptotic) were used to determine the optimal dietary Zn level for broiler chicks (Robbins et al., 1979). Regression analysis was used to estimate Zn optimization (95% of the maximum or minimum response) whenever a significant quadratic or asymptotic response (P < 0.05) was observed (Corzo et al., 2006).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Dietary Zn significantly affected daily BW gain and daily feed intake (P < 0.05) but not the feed/gain ratio (Table 3). When the diet was supplemented with 20 mg of Zn/ kg (48.37 mg/kg total dietary Zn), chick BW gain and feed intake reached a plateau. No additional response was observed at greater Zn concentrations.
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Liver CuZnSOD activity was not affected by the dietary Zn content, but serum 5'-NT activity was influenced significantly (P < 0.0001) and the quadratic response was significant [Y (5'-NT activity) =1.63 + 0.028 x (dietary Zn) – 0.00017X2; R2 = 0.8803; P = 0.0050; Table 4].
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Pancreas and bone ash Zn concentrations were affected by the dietary Zn content significantly (P < 0.0001). As the level of added Zn increased, pancreas Zn and bone Zn increased asymptotically [Y (pancreas Zn) = 57.07 – 27.74e–0.0739X; R2 = 0.9934; P < 0.0001; Y (bone Zn) = 388.50 –221.30e–0.0730X; R2 = 0.9952; P < 0.0001; Table 4
]. However, kidney Zn concentration was not affected by the dietary Zn content. Based on these data, pancreas was more sensitive than kidney, so we chose pancreas for MT concentration and gene expression analysis.
Pancreas MT Concentration and MT and ZnT-2 mRNA Level
The pancreas MT concentration was significantly affected by the dietary Zn content (P < 0.0001). As the level of added Zn increased, pancreas MT concentration increased linearly [Y (pancreas MT) = 8.68 + 0.16X (dietary Zn); R2 = 0.8938; P = 0.0004; Table 5]. The pancreas MT and ZnT-2 mRNA level were significantly affected by the dietary Zn content (P < 0.0001). Pancreas MT mRNA increased linearly as Zn level increased [Y (pancreas MT mRNA) = 1.62 + 0.0043X (dietary Zn); R2 = 0.9690; P < 0.0001; Table 5]. In addition, the quadratic response was significant for pancreas ZnT-2 mRNA [Y (ZnT-2 mRNA) = 0.0305 + 0.0030X (dietary Zn) – 0.000020X2; R2 = 0.9457; P = 0.0029; Table 5].
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The current NRC Zn requirement for chicks (40 mg of Zn/kg from 0 to 3 wk) was based on the level of Zn needed to maximize growth. However, growth may not be the best index of Zn status. When fed with purified or semipurified basal diets, optimal dietary Zn improves the early growth of broilers significantly (Zeigler et al., 1961; Wedekind and Baker, 1990), but when fed with C-SBM diet, growth is usually not influenced (Wedekind et al., 1992). The Zn in C-SBM basal diet often met the estimated requirement of the chick for Zn (40 mg/kg Zn; NRC, 1994). In our study, the Zn in the basal diet was 28.37 mg/kg, lower than 40 mg/kg; when supplemented with 20 mg/kg of Zn (for total dietary Zn of 48.37 mg/kg), chick BW gain and feed intake reached a plateau. That means a total dietary Zn concentration of 48.37 mg/kg is necessary to achieve normal growth in chicks. This result is similar to that reported by Mohanna and Nys (1999), who found that chick BW gain and food intake increased with the dietary Zn content (P < 0.001) until supplementation with 25 mg of Zn/kg (45 mg/kg total dietary Zn) was reached, when chicks were fed a diet supplemented with Zn (added as Zn sulfate) at 0, 10, 25, or 40 mg/kg. These data suggest that the requirement for early chick growth is satisfied when chicks are fed diets containing 40 mg of Zn/kg as recommended by the NRC (1994).
When a corn-soybean meal diet was used, the Zn in the basal diet (often more than 40 mg/kg) met the requirement for chick growth. There was usually no significant change in weight gain by Zn supplemention. On the other hand, weight gain could be influenced by many factors and was not a sensitive criterion for estimation of Zn requirement (Luo et al., 1991). So, weight gain may not be a good index of Zn requirement when a corn-soybean meal diet is used, and criteria other than growth should be chosen to evaluate the Zn requirement.
Tissue concentration, especially in bone, increases with dietary Zn content (Henry et al., 1987). Wedekind et al. (1992) found bone Zn to be an accurate indicator for determining the chick’s Zn requirement, and 60 mg of Zn/ kg was needed when using bone Zn as the criterion. In our study, bone and pancreas Zn yielded similar estimates for Zn requirements (61.70 and 59.75 mg of Zn/kg, respectively). Bone Zn concentration in the present study was in agreement with that reported in other studies with chicks fed similar amounts of Zn (Wedekind et al., 1992). Our study suggested that pancreas was the most sensitive soft tissue to dietary Zn for chicks. This result was supported by McCormick (1984) and Williams et al. (1989).
There have been expectations for many years that assays of the activity of selected Zn metalloenzymes would provide invaluable functional indices of Zn status and possible surrogate biomarkers of dietary Zn (Hambidge, 2003). Although some evidence for the utility of enzyme assays has been reported, none of these have received adequate confirmation (Revy et al., 2006). Indeed, attempts to confirm their utility have often met with negative results (Failla, 1999). Among those that merit further attention are alkaline phosphatase, CuZn-SOD, and 5'-NT in particular (Hambidge, 2003). Because the alkaline phosphatase assay suffers from a lack of specificity, we did not utilize this criterion in our study (Hambidge, 2003). Previous studies have shown that 5'-NT activity may be a sensitive and useful indicator of Zn in pigs (Cepelak et al., 2002), rats (DiSilvestro, 2000), and humans (Davis et al., 2000), but similar studies are not found in chicks. In our study, serum 5'-NT activity was influenced significantly by the dietary Zn content, and the quadratic response was significant, indicating that 5'-NT was a good indicator for Zn status, and also a useful criterion for Zn requirement estimation for chicks. Additionally, liver CuZnSOD activity was not affected by dietary Zn, suggesting that CuZnSOD is not a useful criterion for Zn requirement estimation. This result was support by He et al. (1995).
Pancreas MT and MT mRNA would be considered the weakest markers for Zn requirement because they failed to reach a plateau in our study. Metallothionein is synthesized in tissues in response to dietary Zn (Cousins and Lee-Ambrose, 1992) and allows for binding of excess Zn, thus reducing its potentially harmful effects within the body. The increase in MT with increasing Zn intake has been shown previously in chicks (Sandoval et al., 1998; Cao et al., 2000, 2002) and rats (Reeves, 1995). Cao et al. (2000) found that hepatic and mucosal MT increased linearly when chicks were fed a diet supplemented with 0, 200, or 400 mg of added Zn/kg as reagent-grade Zn sulfate. Hepatic and pancreatic MT concentrations increased when chicks were fed a diet supplemented with 1,000 mg of Zn, as Zn acetate or Zn oxide, per kilogram (Sandoval et al., 1998). In the present study, MT and MT mRNA increased linearly as the dietary Zn level increased, so they were more suitable for analysis of bioavailability of different Zn sources rather than for estimation of Zn requirement. This result was supported by Cao et al. (2002), who found that tissue MT concentration was a useful criterion to evaluate Zn source bioavailability during experiments with chicks fed similar amounts of Zn.
Methodological advances to assess gene expression have provided a new spectrum of research tools to identify individual genes and groups of genes that produce normal and altered physiology. Quantitative real-time PCR provides a highly sensitive and reproducible method for measuring changes in expression of specific genes through transcript sequence detection. The emergence of this new molecular technique is especially promising for the development of a new generation of biomarkers. A notable example is provided by MT mRNA analyses in lymphocytes as a biomarker of Zn status in humans. Levels were markedly reduced with mild experimental dietary Zn restriction (Allan et al., 2000) and increased rapidly with Zn supplementation (Sullivan et al., 1998). Similar results have been found in chicks (Fleet et al., 1988). In accordance with Fleet et al. (1988), our study showed that pancreas MT mRNA linearly increased with dietary Zn supplementation, so it may be a more useful criterion for Zn bioavailability estimation than for Zn requirement.
Mammalian Zn transporters are within 2 gene families: the ZnT proteins and the Zip family. The ZnT and Zip proteins appear to have opposite roles in cellular Zn homeostasis: ZnT transporters reduce intracellular cytoplasmic Zn by promoting Zn efflux from cells or into intracellular vesicles, whereas Zip transporters increase intracellular cytoplasmic Zn by promoting extracellular and perhaps vesicular Zn transport into cytoplasm (Liuzzi and Cousins, 2004). So far, abundant research has been conducted on ZnT proteins in rats, and it has been reported that ZnT members are transcriptionally and posttranslationally regulated by Zn (McMahon and Cousins, 1998; Langmade et al., 2000; Liuzzi et al., 2001). Cousins et al. (2003) reported that Zn-regulated genes, including the Zn transporter genes, have potential uses as markers for assessment of Zn status. Various ZnT members differ in their sensitivity to Zn. Liuzzi et al. (2001) examined, in rats, the comparative response of Zn transporters 1, 2, and 4 to dietary Zn, and demonstrated that ZnT-2 was the most sensitive of the three. There was a strong correlation between the expression of ZnT-2 and MT in response to Zn. However, similar studies have not been conducted in chicks. The present study first observed the effect of dietary Zn on ZnT-2 in chicks, and found that dietary Zn level significantly influenced ZnT-2 mRNA. With the increased dietary Zn level, ZnT-2 fits the quadratic model well, which suggests that ZnT-2 is a useful criterion for Zn requirement estimation.
A nutritional requirement is defined when the variable being measured appears to reach a plateau (Wedekind et al., 2003). In other words, as dietary intake increases, there is no statistically significant increase in variable Y. With this criterion, our study defined a valid Zn requirement using pancreas Zn, bone Zn, serum 5'-NT activity, and pancreas ZnT-2 mRNA level. Requirement values were calculated for pancreas Zn, bone Zn, serum 5'-NT activity, and pancreas ZnT-2 mRNA level by regression with supplemental Zn level. Including the Zn within the basal diet, the estimated Zn requirement was 59.15 mg/kg for pancreas Zn, 61.70 mg/kg for bone Zn, 80.50 mg/kg for 5'-NT activity, and 84.09 mg/kg for pancreas ZnT-2 mRNA level (Table 6). Because pancreas MT and MT mRNA increased linearly as Zn level increased, they were not suitable for Zn requirement analysis.
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FOOTNOTES |
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Received for publication February 22, 2007. Accepted for publication September 8, 2007.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Batal, A. B., T. M. Parr, and D. H. Baker. 2001. Zinc bioavailability in tetrabasic zinc chloride and dietary zinc requirement of young chicks fed a soy concentrate diet. Poult. Sci. 80:87–90.
Burrell, A. L., W. A. Dozier, A. J. Davis, M. M. Compton, M. E. Freeman, P. F. Vendrell, and T. L. Ward. 2004. Response of broilers to dietary zinc concentrations and sources in relation to environmental implications. Br. Poult. Sci. 45:255–263.[Web of Science][Medline]
Cao, J., P. R. Henry, S. R. Davis, R. J. Cousins, R. D. Miles, R. C. Littell, and C. B. Ammerman. 2002. Realtive bioavailability of organic zinc sources based on tissue zinc and metallothionein in chicks fed conventional dietary zinc concentrations. Anim. Feed Sci. Technol. 101:161–170.[CrossRef]
Cao, J., P. R. Henry, R. Guo, R. A. Holwerda, J. P. Toth, R. C. Littell, R. D. Miles, and C. B. Ammerman. 2000. Chemical characteristics and relative bioavailability of supplemental organic zinc sources for poultry and ruminants. J. Anim. Sci. 78:2039–2054.
Cepelak, I., K. Barisic, S. Luterotti, B. Sokolic, and V. Rupic. 2002. Zinc-dependent enzymes as indicators of zinc status in swine. Periodicum Biologorum. Hrvatsko Prirodoslovno Drustvo, Zagreb, Croatia. 104:445–450.
Corzo, A., W. A. Dozier, III, and M. T. Kidd. 2006. Dietary lysine needs of late-developing heavy broilers. Poult. Sci. 85:457–461.
Cousins, R. J. 1996. Zinc. Pages 293–306 in Present Knowledge in Nutrition. L. J. Filer, and E. E. Ziegler, ed. Int. Life Sci. Inst. Nutr. Found., Washington, DC.
Cousins, R. J., R. K. Blanchard, M. P. Popp, L. Liu, J. Cao, J. Bernadette Moore, and C. L. Green. 2003. A global view of the selectivity of zinc deprivation and excess on genes expressed in human THP-1 mononuclear cells. Proc. Natl. Acad. Sci. USA 100:6952–6957.
Cousins, R. J., and L. M. Lee-Ambrose. 1992. Nuclear zinc uptake and interactions and metallothionein gene expression are influenced by dietary zinc in rats. J. Nutr. 122:56–64.
Davis, C. D., D. B. Milne, and F. H. Nielsen. 2000. Changes in dietary zinc and copper affect zinc-status indicators of post-menopausal women, notably, extracellular superoxide dismutase and amyloid precursor proteins. Am. J. Clin. Nutr. 71:781–788.
DiSilvestro, R. A. 2000. Zinc in relation to diabetes and oxidative disease. J. Nutr. 130:1509s–1511s.[Web of Science][Medline]
Eaton, D. L., and B. F. Toal. 1982. Evaluation of the Cd/hemoglobin affinity assay for the rapid determination of metallothionein in biological tissues. Toxicol. Appl. Pharmacol. 66:134–142.[CrossRef][Web of Science][Medline]
Edwards, H. M., R. J. Young, and M. B. Gillis. 1958. Studies on zinc in poultry nutrition. 1. The effect of feed, water and environment on zinc deficiency in chicks. Poult. Sci. 37:1094–1099.[Web of Science]
Emmert, J. L., and D. H. Baker. 1995. Zinc stores in chickens delay the onset of zinc deficiency symptoms. Poult. Sci. 74:1011–1021.[Web of Science][Medline]
Failla, M. L. 1999. Considerations for determining ‘optimal nutrition’ for copper, zinc, manganese and molybdenum. Proc. Nutr. Soc. 58:497–505.[Web of Science][Medline]
Fleet, J. C., M. A. Qureshi, R. R. Dieter, and C. C. McCormick. 1988. Tissue-specific accumulation of metallothionein in chickens as influenced by the route of zinc administration. J. Nutr. 118:176–182.
Hambidge, M. 2003. Biomarkers of trace mineral intake and status. J. Nutr. 133:948S–955S.
He, T., H. L. Liu, L. Liang, and C. Z. Liu. 1995. Study on zinc requiremental parameters of broilers. Acta Zoonutr. Sin. 7:2–9.
Henry, P. R., C. B. Ammerman, and R. D. Miles. 1987. Effect of dietary zinc on tissue mineral concentration as a measure of zinc bioavailability in chicks. Nutr. Rep. Int. 35:15–20.[Web of Science]
Langmade, S. J., R. Ravindra, P. J. Daniels, and G. K. Andrews. 2000. The transcription factor MTF-1 mediates metal regulation of the mouse ZnT1 gene. J. Biol. Chem. 275:34803–34809.
Li, S., X. Luo, B. Liu, T. D. Crenshaw, X. Kuang, and G. Shao. 2004. Use of chemical characteristics to predict relative bio-availability of supplemental organic manganese sources for broilers. J. Anim. Sci. 82:2352–2363.
Lichtlen, P., Y. Wang, T. Belser, O. Georgiev, U. Certa, R. Sack, and W. Schaffner. 2001. Target gene search for the metal-responsive transcription factor MTF-1. Nucleic Acids Res. 29:1514–1523.
Liuzzi, J. P., R. K. Blanchard, and R. J. Cousins. 2001. Differential regulation of zinc transporter 1, 2, and 4 mRNA expression by dietary zinc in rats. J. Nutr. 131:46–52.
Liuzzi, J. P., and R. J. Cousins. 2004. Mammalian zinc transporters. Annu. Rev. Nutr. 24:151–172.[CrossRef][Web of Science][Medline]
Luo, X. G., Q. Su, J. C. Huang, and J. X. Liu. 1991. A study on the optimal manganese (Mn) level in a practical diet of broiler chicks. Chin. J. Anim. Vet. Sci. 22:313–317.
McCormick, C. C. 1984. Induction and accumulation of metallothionein in liver and pancreas of chicks given oral zinc: a tissue comparison. J. Nutr. 114:191–203.
McMahon, R. J., and R. J. Cousins. 1998. Regulation of the zinc transporter ZnT-1 by dietary zinc. Proc. Natl. Acad. Sci. USA 95:4841–4846.
Mohanna, C., and Y. Nys. 1999. Effect of dietary zinc content and sources on the growth, body zinc deposition and retention, zinc excretion and immune response in chickens. Br. Poult. Sci. 40:108–114.[CrossRef][Web of Science][Medline]
Morrison, A. B., and H. P. Sarett. 1958. Studies of zinc deficiency in the chick. J. Nutr. 65:267–280.
National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC.
Oyanagui, Y. 1984. Reevaluation of assay methods and establishment of kit for superoxide dismutase activity. Anal. Biochem. 142:290–296.[CrossRef][Web of Science][Medline]
Reeves, P. G. 1995. Adaptation responses in rats to long-term feeding of high-zinc diets: Emphasis on intestinal metallothionein. J. Nutr. Biochem. 6:48–54.[CrossRef][Web of Science]
Revy, P. S., C. Jondreville, J. Y. Dourmad, and Y. Nys. 2006. Assessment of dietary zinc requirement of weaned piglets fed diets with or without microbial phytase. J. Anim. Physiol. A. Anim. Nutr. 90:50–59.[CrossRef]
Robbins, K. R., H. W. Norton, and D. H. Baker. 1979. Estimation of nutrient requirements from growth data. J. Nutr. 109:1710–1714.
Roberson, R. H., and P. J. Schaible. 1958. The zinc requirement of the chick. Poult. Sci. 37:1321–1323.[Web of Science]
Sandoval, M., P. R. Henry, X. G. Luo, R. C. Littell, R. D. Miles, and C. B. Ammerman. 1998. Performance and tissue zinc and metallothionein accumulation in chicks fed a high dietary level of zinc. Poult. Sci. 77:1354–1363.
SAS Institute. 1996. SAS User’s Guide: Statistics. Version 7.0 ed. SAS Inst. Inc., Cary, NC.
Sterling, K. G., D. V. Vedenov, G. M. Pesti, and R. I. Bakalli. 2005. Economically optimal dietary crude protein and lysine levels for starting broiler chicks. Poult. Sci. 84:29–36.
Sullivan, V. K., F. R. Burnett, and R. J. Cousins. 1998. Metallothionein expression is increased in monocytes and erythrocytes of young men during zinc supplementation. J. Nutr. 128:707–713.
Waldroup, P. W. 2004. Dietary nutrient allowances for chickens and turkeys. Feedstuffs 76:42–47.
Wedekind, K. J., and D. H. Baker. 1990. Zinc bioavailability in feed-grade sources of zinc. J. Anim. Sci. 68:684–689.[Abstract]
Wedekind, K. J., A. E. Hortin, and D. H. Baker. 1992. Methodology for assessing zinc bioavailability: Efficacy estimates for zinc-methionine, zinc sulfate, and zinc oxide. J. Anim. Sci. 70:178–187.[Abstract]
Wedekind, K. J., A. J. Lewis, M. A. Giesemann, and P. S. Miller. 1994. Bioavailability of zinc from inorganic and organic sources for pigs fed corn-soybean meal diets. J. Anim. Sci. 72:2681–2689.[Abstract]
Wedekind, K. J., S. Yu, and G. F. Combs. 2003. The selenium requirement of the puppy. J. Anim. Physiol. A. Anim. Nutr. 88:340–347.
Williams, S. N., R. D. Miles, M. D. Ouart, and D. R. Campbell. 1989. Short-term high level zinc feeding and tissue zinc concentration in mature laying hens. Poult. Sci. 68:539–545.[Web of Science][Medline]
Zeigler, T. R., R. M. Leach, L. Jr, C. Norris, and M. L. Scott. 1961. Zinc requirement of the chick: Factors affecting requirement. Poult. Sci. 40:1584–1593.[Web of Science]
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 Y. Yu, L. Lu, X. G. Luo, and B. Liu Kinetics of Zinc Absorption by In Situ Ligated Intestinal Loops of Broilers Involved in Zinc Transporters Poult. Sci., June 1, 2008; 87(6): 1146 - 1155. [Abstract] [Full Text] [PDF]
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