Dietary Zinc Levels Research Articles

Identification of mutations in Caenorhabditis elegans that cause resistance to high levels of dietary zinc and analysis using a genomewide map of single nucleotide polymorphisms scored by pyrosequencing.

Zinc plays many critical roles in biological systems: zinc bound to proteins has structural and catalytic functions, and zinc is proposed to act as a signaling molecule. Because zinc deficiency and excess result in toxicity, animals have evolved sophisticated mechanisms for zinc metabolism and homeostasis. However, these mechanisms remain poorly defined. To identify genes involved in zinc metabolism, we conducted a forward genetic screen for chemically induced mutations that cause Caenorhabditis elegans to be resistant to high levels of dietary zinc. Nineteen mutations that confer significant resistance to supplemental dietary zinc were identified. To determine the map positions of these mutations, we developed a genomewide map of single nucleotide polymorphisms (SNPs) that can be scored by the high-throughput method of DNA pyrosequencing. This map was used to determine the approximate chromosomal position of each mutation, and the accuracy of this approach was verified by conducting three-factor mapping experiments with mutations that cause visible phenotypes. This is a generally applicable mapping approach that can be used to position a wide variety of C. elegans mutations. The mapping experiments demonstrate that the 19 mutations identify at least three genes that, when mutated, confer resistance to toxicity caused by supplemental dietary zinc. These genes are likely to be involved in zinc metabolism, and the analysis of these genes will provide insights into mechanisms of excess zinc toxicity.

Effects of copper sulfate, tri-basic copper chloride, and zinc oxide on weanling pig growth and plasma mineral concentrations (2008)

Two 28-d experiments were conducted to determine the effects of increasing dietary zinc and copper levels on weanling pig performance. In each experiment, 180 weanling pigs (PIC, 21 d of age, 12.5 lb in Exp. 1 and 13.2 lb in Exp. 2) were allotted to 1 of 6 treatments with 5 and 6 replications in Exp. 1 and 2, respectively. Diets were fed in 2 phases (d 0 to 14 and 14 to 28), and the trace mineral premix provided 165 ppm zinc and 16.5 ppm copper to all diets. In Exp. 1, treatments were arranged as a 2 × 3 factorial with 2 levels of added copper from tri-basic copper chloride (TBCC; 0 or 150 ppm) and 3 levels of added zinc from zinc oxide (0, 1,500, or 3,000 ppm from d 0 to 14 and 0, 1,000, or 2,000 ppm from d 14 to 28). In addition, blood collected on d 14 was analyzed for plasma zinc, copper, and phosphorus concentrations. No copper × zinc interactions were observed (P > 0.25) for any of the growth data. Addition of TBCC increased (P < 0.03) ADG and ADFI over control pigs from d 0 to 14, 14 to 28, and 0 to 28. Pigs fed increasing dietary zinc had increased (linear, P < 0.003) ADFI during both phases and increased ADG from d 0 to 14 and 0 to 28. No effects were observed for blood metabolites in plasma copper; however, copper × zinc interactions were observed (P < 0.03) for both plasma zinc and phosphorus. The interactions occurred because increasing dietary zinc oxide increased plasma zinc and phosphorus when TBCC was not included in the diet but had relatively little effect when TBCC was added to the diet.

An Optimal Dietary Zinc Level of Broiler Chicks Fed a Corn-Soybean Meal Diet

An experiment was conducted to estimate the optimal dietary zinc level for broiler chicks fed a corn-soybean meal diet. A total of 384 one-day-old male broiler chicks were assigned randomly to dietary treatments for 21 d. These treatments included a basal corn-soybean meal diet (28.32 mg of Zn/kg) supplemented with 0, 20, 40, 60, 80, 100, 120, or 140 mg of Zn/kg in the form of reagent-grade ZnSO4·7H2 O. All treatments were replicated 6 times using 8 chicks per pen. Tissue Zn concentration, Zn metalloenzyme activity, metallothionein (MT) concentration, MT mRNA level, and Zn transporter-2 (ZnT-2) mRNA level were analyzed for choosing suitable criterion to determine the optimal dietary Zn level for broilers. Regression analysis was performed to estimate optimal dietary Zn level in the presence of quadratic or asymptotic responses. Results showed that weight gain and feed intake were increased with dietary Zn level (P < 0.05), and the maximum weight gain and feed intake were observed in the diet supplemented with 20 mg of Zn/kg (48.37 mg/kg, total dietary Zn). Pancreas MT and MT mRNA increased linearly with Zn supplementation. According to the asymptotic model, the optimal Zn requirement of chicks from hatch to 21 d of age was 59.15 mg/kg for pancreas Zn and 61.70 mg/kg for bone Zn respectively. Quadratic responses were exhibited by serum 5′-nucleotidase activity and pancreas Zn transporter-2 mRNA level, resulting in total optimal dietary levels of 80.50 and 84.09 mg/kg, respectively. Based on results from this study, the optimal dietary Zn level of chicks from hatch to 21 d of age is 84 mg/kg.

Consumption of a moderately Zn-deficient and Zn-supplemented diet affects soluble protein expression in rat soleus muscle

Zinc deficiency negatively affects muscle function, but there are limited biochemical data identifying the cause of this reduction in function. The objective of the present study was to identify soluble proteins in rat soleus muscle that were responsive to different levels of dietary zinc. Rats ( n=21) were fed diets containing three concentrations of zinc: 5, 30 and 200 ppm for 42 days. There was no difference in body weights of the rats consuming the 5-ppm zinc diet compared to the rats consuming the 30- or 200-ppm zinc diets; however, bone zinc levels were significantly decreased in the 5-ppm dietary zinc group. Individual soluble protein fractions were isolated from these muscles and the samples were prepared for two-dimensional polyacrylamide gel electrophoresis. The expression levels of four proteins were significantly depressed by dietary Zn depletion and supplementation, S-glutathiolated carbonic anhydrase, myosin light polypeptide 3, heat shock protein 20 and heart fatty acid binding protein. This is the first report that indicates that both Zn depletion and supplementation result in protein expression profiles that may negatively affect skeletal muscle function. These results indicate that there are specific signaling pathways that require proper Zn nutriture for maintaining optimal muscle function and suggest that the consumption of pharmacologic doses of Zn may be detrimental to muscle function.

Effects of level and form of dietary zinc on dairy cow performance and health

It is well established that zinc is an essential micro-nutrient required to maintain health and performance in dairy cows (Underwood and Suttle, 2004). Cattle diets are traditionally supplemented with inorganic minerals (e.g. zinc oxide), but these may be poorly absorbed, resulting in an economic and environmental cost due to excess minerals being excreted. It is claimed organically bound minerals are able to resist interaction before and at the absorption site in the small intestine (Power, 2006), which may result in a lower dietary inclusion rate being required. The objective of the current experiment was to investigate the effect of an organically bound source of Zn as a replacement for inorganic Zn on dairy cow health and performance when supplemented at and below the recommended level.

Reduced Use of Antibiotic Growth Promoters in Diets Fed to Weanling Pigs: Dietary Tools, Part 1

Antibiotics improve health and productive performance of pigs. There is increasing evidence that other dietary ingredients may provide similar, but probably not identical, benefits. A properly prepared immune egg product, spray-dried plasma, or a high level of dietary zinc can provide protection against enteric infection in young pigs. Spray-dried plasma also increases growth rate dramatically, and zinc increases it substantially. The evidence in refereed publications also indicates that organic acids increase growth rate substantially, but does not clearly identify the most effective acid or combination of acids. Whey proteins, lactose, mannan oligosaccharide, or a high level of dietary copper provides a modest but useful increase in growth rate. It is not clear whether conventional egg products or other milk proteins may be beneficial. There are many other feed ingredients commercially available that may improve health and productive performance of pigs.

Influence of Different Dietary Levels of Zinc on Performance, Vitamin B12, and Blood Parameters in Lambs

This experiment was conducted to investigate the influence of different dietary levels of zinc (Zn) on performance, vitamin B12, and blood parameters in lambs. Thirty six cannulated Poll Dorset x Small-tailed Han wether lambs were assigned randomly to four treatment groups: The control group, which was supplemented with 0.30 mg Co/kg dry matter (DM) to the basal diet; and the low-, medium- and high-Zn supplemented groups, supplementation of 50, 100, and 150 mg Zn/kg DM to the control diet, respectively. Lambs were housed in individual pens and the experiment lasted for 70 days. There was no significant difference in body weight gain and feed/gain between different treatment groups. The high-Zn supplemented lambs showed lower vitamin B12 concentrations in both ruminal fluid and plasma, and higher methylmalonic acid and homocysteine concentrations in plasma compared with the control and low-Zn supplemented groups (p < 0.05). No significant difference was observed in these biochemical values between the control, the low-, and the medium-Zn supplemented groups (p > 0.05). Plasma folate concentration, glucose, and heme-dependent blood parameters were not influenced by dietary zinc level. It was concluded that the higher level of zinc supplementation had a negative effect on vitamin B12 in lambs. Higher inclusion level of dietary zinc could inhibit vitamin B12 synthesis in the rumen of lambs.

Effect of dietary zinc level on serum carotenoid levels, body and shank pigmentation of chickens after experimental infection with coccidia

Two experiments were conducted to test the effects of a dietary zinc amino acid complex (Zn-AA) and an anticoccidial drug on Eimeria acervulina or Eimeria tenella infections. In each experiment, 288 day-old Three-Yellow-Chickens were used in a 2 × 3 factorial experimental design. Six groups were arranged randomly to receive three levels of Zn-AA (0, 40, or 80 mg/kg) alone or with salinomycin (60 mg/kg). Additionally an uninfected group was set as negative control. At the age of 21 days birds in Exp. 1 were inoculated with 3 · 104 sporulated E. acervulina oocysts, while birds in Exp. 2 were inoculated with 1.5 · 104 sporulated E. tenella oocysts. In Exp. 1, E. acervulina did not suppress growth performance significantly, but in groups without salinomycin it significantly reduced serum carotenoid levels on day 7 after inoculation and body and shank pigmentation on day 42. Salinomycin medication maintained serum carotenoids and visual colour of inoculated birds, but Zn-AA did not influence these parameters. In Exp. 2, growth performances of infected and uninfected chickens were similar. Infection decreased to only serum carotenoid levels on day 14 after infection, and colour scores on day 42 in the inoculated group without salinomycin and Zn-AA supplementation. The birds that received Zn-AA had significantly higher serum carotenoid levels and colour scores than those that did not. Although supplementation of Zn-AA cannot avoid coccidial damage of caecum, it prevents the reduction of serum carotenoids and pigmentation of Three-Yellow-Chicken infected with E. tenella, but not after infection with E. avervulina. The interactive effects between Zn-AA and salinomycin on growth performance and pigmentation were not significant.

Pesticides and Essential Minerals Modify Endogenous Antioxidants and Cytochrome P450 in Tissues of Rats

Two experiments were conducted in male Sprague Dawley (SD) rats (175–200 g) to determine changes in the activities of endogenous antioxidants superoxide dismutase (SOD), glutathione peroxidase (GPX), cytochrome P450 (ethoxyresorufin deethylase; EROD) and concentrations of glutathione (GSH) in the blood, liver, and small intestinal mucosa (IM). In both experiments, six rats/group were fed diets based on the AIN-93M diet (Control) or the same modified to contain either 500 mg calcium (Low Ca), 7 mg Zn (Low Zn): 2 mg copper (Low Cu), 60 mg zinc (High Zn) or 12 mg copper (High Cu) in the following combination: Control, LCa/LZn, LCa/LZn/LCu, or HZn/HCu, with and without a pesticide mixture containing acephate, endosulfan, and thiram at 25% LD50 for four or two weeks. Pesticides decreased feed intake and weight gain in all groups by 28%. Erythrocyte SOD was higher than control in the HZn/HCu group and in the LCa/LZn/LCu and HZn/HCu groups with pesticide (P# 0.05). Plasma GPX declined by more than 55% in all the groups with and without pesticides compared to the control. The LCa/LZn/LCu and HZn/HCu diets with and without pesticides reduced GPX in the IM by up to 88%, 40%, and 74%, respectively, than the control. Plasma GSH was about 20% higher than the control in most groups with and without pesticides in the diet. Liver and IM GSH were higher than the control in the HZn/HCu group, whereas IM GSH concentrations were lower than the control in the LCa/LZn and LCa/LZn/LCu groups (P#0.05). All three experimental diets with and without pesticides had a significant effect on liver EROD activity (P#0.05). The results indicate that endogenous antioxidants and EROD were independently modified by dietary zinc and copper levels and pesticides.

Supplementation of zinc from organic or inorganic source improves performance and antioxidant status of heat-distressed quail

Two sources of zinc [ZnSO4.H2O or ZnPicolinate (ZnPic)] supplementation were evaluated for their effects on performance, carcass weight, levels of malondialdehyde, and vitamins C, E, A in Japanese quail (Coturnix coturnix Japonica) exposed to high ambient temperature of 34 degrees C. The birds (n = 360; 10-d-old) were randomly assigned to 12 treatment groups consisting of 3 replicates of 10 birds each in a 2 × 2 × 3 factorial arrangement of treatments (temperatures, zinc sources, zinc levels). Birds were kept in wire cages in a temperature-controlled room at either 22 degrees C (thermoneutral) or 34 degrees C (heat stress) for 8 h/d (0900 to 1700 h) until the end of study, and fed a basal (control) diet or the basal diet supplemented with either 30 or 60 mg of Zn as ZnSO4 H2O or ZnPic/kg of diet. Heat exposure decreased (P = 0.001) live weight gain, feed intake, feed efficiency, and carcass weight when the basal diet was fed. A linear increase in feed intake (P = 0.01) and BW (P = 0.01), and improvement in feed efficiency (P = 0.01) and carcass weight (P < or = 0.05) were found in zinc-supplemented quail reared under heat-stress conditions. Serum vitamin C (P = 0.04), E (P = 0.05), and cholesterol (P = 0.01) concentrations increased linearly, whereas malondialdehyde concentrations decreased linearly (P = 0.02) as dietary zinc sulfate and ZnPic supplementation increased. An interaction between dietary zinc sources, temperature, and levels of supplementation (P < or = 0.05) for these parameters was detected. Serum vitamins C, E, and A concentrations were not different in supplemented birds reared at thermoneutral temperature. Supplementation with zinc improved carcass weight and antioxidant status of birds, and the effects of ZnPic were relatively greater than those of ZnSO4.H2O in heat-stressed quail. Results of the present study suggest that supplementation with ZnPic could be considered to be more protective than ZnSO4.H2O by reducing the negative effects of oxidative stress induced by heat stress in quail.

Protection by dietary zinc in ALS mutant G93A SOD transgenic mice

Mutations to the copper, zinc superoxide dismutase (SOD) gene are responsible for 2–3% of amyotrophic lateral sclerosis (ALS) cases. These mutations result in the protein having a reduced affinity for zinc. SOD becomes toxic to motor neurons when zinc is missing from its active site. Recently, high dosages of zinc (75 and 375 mg/kg/day) have been paradoxically reported to increase the death of G93A-mutant SOD transgenic mice [G.J. Groeneveld, J. de Leeuw van Weenen, F.L. van Muiswinkel, H. Veldman, J.H. Veldink, J.H. Wokke, P.R. Bar, L.H. van den Berg, Zinc amplifies mSOD1-mediated toxicity in a transgenic mouse model of amyotrophic lateral sclerosis, Neurosci. Lett. 352 (2003) 175–178]. In contrast, we have found that moderate supplementation of zinc (∼12 mg/kg/day) delayed death in G93A-mutant SOD mice by 11 days compared to mice on a zinc-deficient diet. Supplementing zinc with even 18 mg/kg/day resulted in a more rapid death of some mice, consistent with the results of Groenevelt et al. However, large amounts of zinc competitively inhibit copper absorption, which inhibits the copper-dependent ceruloplasmin, and can cause a lethal anemia. We found that supplementing the 18 mg/kg/day dosage of zinc with 0.3 mg/kg/day of copper prevented the early death from zinc treatment alone. These data support a role for moderate levels of dietary zinc potentially protecting against the toxicity of ALS-associated SOD and the protection does not result from depleting copper.

Normal Growth Rate in Rats Is Recovered After a Period of Zinc Deficiency by Restoration of Zinc Supply by Means of a Zinc-Fortified Petit Suisse Cheese

Fortification of a Petit Suisse cheese with zinc sulfate and zinc gluconate stabilized with glycine was used as a tool to overcome zinc-deficiency effects on total-body growth and skeletal growth. Animals were divided in 4 groups of 10 rats: basal (B), control (C), depletion-repletion 1 (DR1), and depletion-repletion 2 (DR2). These four groups were fed with four diets: basal (2 ppm Zn), control (30 ppm Zn), DR1, and DR2; they received a basal diet for 14 d and a control diet for the other 14 d of the experiment, using zinc sulfate for DR1 and zinc gluconate stabilized with glycine for DR2. After 28 d of the experiment, total-body weight and weight gain of the control and DR1 and DR2 animals were not statistically different (p<0.05), Femur weight and femur zinc content of DR1 and DR2 did not achieve the values of control animals (p<0.05), but they were higher than that of basal animals. Our results show that restoration of dietary zinc levels by means of food fortification normalized weight gain, as an indicator of total-body growth, and presented a trend to normalize bone weight, as a marker of skeletal growth, in young rats and independently of the zinc source used.

Effects of Dietary Zinc Levels on the Activities of Enzymes, Weights of Organs, and the Concentrations of Zinc and Copper in Growing Rats

Zinc (Zn) is an essential nutrient that is required in humans and animals for many physiological functions, including immune and antioxidant function, growth, and reproduction. The present study was performed to investigate the effects of three Zn levels, including Zn adequate (35.94 mg/kg, as a control), Zn deficiency (3.15 mg/kg), and Zn overload (347.50 mg/kg) in growing male rats for 6 wk. This allowed for evaluation of the effects that these Zn levels might have on body weight, organ weight, enzymes activities, and tissues concentrations of Zn and Cu. The results showed that Zn deficiency has negative effects on growth, organ weight, and biological parameters such as alkaline phosphatase (ALP) and Cu-Zn superoxide dismutase (Cu-Zn SOD) activities, whereas Zn overload played an effective role in promoting growth, improving the developments of organs and enhancing immune system. Hepatic metallothionein (MT) concentration showed an identical increase tendency in rats fed both Zn-deficient and Zn-overload diets. The actual mechanism of reduction of Cu concentration of jejunum in rats fed a Zn-overload diet might involve the modulation or inhibition of a Cu transporter protein by Zn and not by the induction of MT.

Effects of dietary zinc levels, phytic acid and resistant starch on zinc bioavailability in rats

Owing to its fermentability, it has been advocated that resistant starch (RS) has a positive effect on the absorption of minerals by increasing their solubility in the hindgut. In marginally zinc-deficient rats, the enhancement of zinc bioavailability by RS occurs mostly when the diet contains phytic acid. This study aims to investigate the effect of dietary zinc level and phytic acid on the cecal zinc pools and zinc bioavailability of rats fed RS. Wistar rats (male, 3wk old) were divided into eight groups (n = 6), and fed diets containing either 5% cellulose (control fiber: insoluble and low fermentable) or 20 % RS (test fiber: soluble and fermentable), with or without the addition of 1% sodium phytate, at the 10 and 30 mg/kg dietary zinc levels, for 21 days. At 10 mg Zn/kg, RS increased femur zinc concentration only in the group receiving the phytate-containing diet, while at 30 mg Zn/kg it increased femur zinc concentration in rats fed both phytate-free and phytate-containing diets. The total content of zinc in the cecum was increased by the higher dietary zinc level and tended to be increased by the addition of phytate, which is assumed to impair zinc absorption in the small intestine. Feeding RS lowered cecal pH values, which correlated with increasing values of zinc solubility (r = -0.3471; P < 0.05). The later was, in turn, directly associated with zinc apparent absorption (r = 0.3739; P < 0.05). The increase in zinc bioavailability by RS occurs when dietary zinc levels are adequate and/or zinc absorption is impaired in the small intestine, increasing the influx of unabsorbed zinc into the cecum and favoring the increase of zinc bioavailability when RS fermentation lowers the cecal pH.

Additional dietary zinc for weaning piglets is associated with elevated concentrations of serum IGF-I.

Two experiments were performed in order to study how weaning and post-weaning dietary zinc level affect serum IGF-I. Further, whether the growth-enhancing effect of 2500 ppm of dietary zinc (Zn2500) and/or 175 ppm of dietary copper (Cu175) in post-weaning diets is associated with elevated serum IGF-I levels in piglets was studied. Experiment 1 included 54 piglets (six litters of nine piglets). One piglet from every litter was assigned to a control group (blood sampled 1 day before weaning). At weaning the remaining eight piglets from every litter were allocated randomly to four dietary treatments with increasing zinc inclusions (Zn100, Zn250, Zn1000, Zn2500). In exp. 2, 48 piglets (six litters of eight piglets) were allocated to four dietary treatments (Zn100, Zn100Cu175, Zn2500, Zn2500Cu175). All piglets in exp. 1 were blood sampled at -1, 1-2, 5-6 or 14-15 days after weaning and in exp. 2 blood samples were taken from all pigs 5-7 days after weaning. Feed intake was recorded per pen (two piglets) and weight gain was recorded for every piglet. Just after weaning feed intake was very low, piglets lost weight and serum IGF-I decreased in exp. 1. However, the piglets fed 2500 ppm of zinc reached pre-weaning levels of serum IGF-I at 14-15 days post-weaning, whereas piglets receiving lower zinc levels showed no changes in serum IGF-I. In exp. 2, additional dietary zinc in weaning diets for piglets was found to be associated with increased feed intake, improved growth rate and increased serum IGF-I. High levels of dietary copper did not affect any of these measurements. Zinc-induced rise in serum IGF-I was partly due to increased feed intake. After correcting for differences in feed intake, zinc significantly increased serum IGF-I. However, to completely separate effects of feed intake from effects of zinc status, pair-feeding should be considered in future studies.

Bioavailability of zinc from zinc sulfate and different organic zinc sources and their effects on ruminal volatile fatty acid proportions

Twenty-four Angus steers were used to determine the effects of dietary zinc (Zn) level and source on Zn metabolism and ruminal volatile fatty acid (VFA) patterns. All steers were fed a low Zn diet (18.8 mg Zn per kg) for 42 days prior to assignment to dietary treatments. Treatments consisted of: (1) control (low Zn diet), (2) Zn sulfate (ZnSO 4), (3) Zn methionine complex (ZnMet) and (4) Zn glycine complex (ZnGly). The Zn sources were added to provide 20 mg of supplemental Zn per kg diet. A 5-day total collection of feces and urine was conducted beginning on day 14 of the study. Liver biopsy samples were obtained on days 0 and 42 for Zn analysis, and ruminal fluid was collected on day 42 for VFA and ruminal soluble Zn determination. Plasma samples were obtained on days 0, 2, 19, 21, and 42 for determination of plasma Zn and alkaline phosphatase activity. Urinary excretion of Zn was higher ( P<0.05) in steers supplemented with ZnMet or ZnGly than in controls. Apparent absorption and retention of Zn were not significantly affected by treatment, but tended to be higher in steers receiving ZnGly. Liver Zn concentrations were higher ( P<0.05) on day 42 in steers supplemented with ZnGly, compared to steers receiving control, ZnMet or ZnSO 4 treatments. Plasma Zn concentrations were higher ( P<0.05) for the ZnGly and ZnMet treatments compared to the control on day 42. Plasma alkaline phosphatase was not affected by treatment. Ruminal soluble Zn concentrations were higher ( P<0.05) in steers fed ZnMet compared to those fed the control or ZnSO 4 diets. Total VFA concentrations were higher ( P<0.05) in steers fed the control and ZnSO 4 treatments than in those receiving ZnGly or ZnMet. Steers supplemented with ZnMet had a higher ( P<0.05) molar proportion of propionate and lower ( P<0.05) molar proportions of butyrate and valerate than controls. Compared to the control treatment, valerate was the only VFA affected by ZnSO 4 or ZnGly supplementation. Results suggest that Zn from ZnGly was more bioavailable than ZnSO 4 or ZnMet. However, ZnMet supplementation resulted in the highest ruminal soluble Zn concentrations and altered ruminal VFA proportions to the greatest extent of the Zn sources evaluated.

Effect of dietary protein, zinc, and carbon monoxide on fetal zinc concentration in mice.

Dietary protein and zinc deficiencies known to be detrimental to the developing fetus are common in pregnant women in developing countries. Everyone in modern society is at risk of exposure to carbon monoxide (CO). This study was conducted to observe the effect of dietary protein, zinc, and exposure to CO on the fetal zinc concentrations by factorial experimentation. Pregnant mice of CD-1 strain were maintained on 17% (control) or 9% (deficient) protein diets mixed with deficient, normal (control), or supplemental zinc throughout gestation. The dams in each dietary group were exposed to air (control) or 500 ppm CO in air in environmental chambers from gestation day 8 to gestational day 18. The dams were sacrificed on d 18 and fetal zinc levels were measured by atomic absorption spectrophotometry. Carbon monoxide levels used in this study had no significant effect on fetal zinc concentration in any treatment group. When both dietary protein and zinc levels were normal, the mean fetal zinc concentrations were higher than all other dietary protein/zinc combinations (15.2 +/-6.0 and 14.2 +/- 4.1 microg Zn/g of tissue for 0 and 500 ppm CO levels). However, when dietary protein levels were deficient, supplemental zinc increased the fetal zinc concentrations significantly (12.7+/-3.8 and 13.1+/-0.3.6 microg Zn/g of tissue, in 0 and 500 ppm CO groups) as compared to zinc-deficient groups (8.7 +/- 3.0 and 10.0 +/- 3.3 microg Zn/g of tissue in 0 and 500 ppm CO groups). The results of this study may be relevant to populations that experience both marginal zinc and protein diets during gestation.

Effect of dietary zinc level on absorption and tissue distribution of zinc in rats

Effect of dietary zinc level on absorption and tissue distribution of zinc in rats

Effects of different levels of zinc on the performance and immunocompetence of broilers under heat stress

Male broilers were used to evaluate the effect of zinc on performance and immune competence during heat stress (HS). Broilers raised in either a thermoneutral (TN, 23.9 degrees C constant) or HS (23.9 to 35 degrees C cycling) environment were fed a low zinc diet (LZ; 34 mg/kg), an adequate zinc diet (AZ; 68 mg/kg), or a supplemental zinc diet (HZ; 181 mg/kg). Humoral immunity was assessed by intravenous injection of 7% SRBC followed by evaluation of serum for antibody titers in primary and secondary responses. Cell-mediated immunity was assessed using a Sephadex stimulation method to recruit abdominal exudate cells (AEC) to evaluate macrophage phagocytic ability. The HS birds consumed 12.5% less feed, gained 24.6% less weight, and had lower feed efficiency when compared to TN birds. Dietary zinc levels did not impact growth performance or plasma zinc concentration. Numbers of AEC, macrophages in AEC, phagocytic macrophages, and internalized opsonized and unopsonized SRBC were increased by HZ. Total, IgM, and IgG antibody titers for primary and secondary responses were significantly increased in birds receiving HZ under TN conditions. Tibia zinc concentration increased with increasing zinc levels but did not change with temperature. Lymphoid organ weights, primary and secondary antibody responses, incidences of macrophages in AEC, phagocytic ability of macrophages, and plasma zinc concentration were all significantly reduced by HS. These results indicate that the immune response of broilers can be influenced by the level of zinc in the diet and by environmental conditions.

Effects of dietary zinc on the shell biomineralization in abalone Haliotis discus hannai Ino

A study was conducted to investigate the relationship between dietary zinc and shell biomineralization in abalone Haliotis discus hannai Ino. Seven triplicate groups of juvenile abalone (mean weight: 0.74±0.01 g; mean shell length: 16.41±0.04 mm) were fed with one of seven semi-purified diets containing graded levels of dietary zinc (5.6, 10.7, 15.1, 25.2, 34.7, 45.3 and 84.6 mg/kg). To better understand the effects of dietary zinc on the shell deposition, the newly grown shell (NS) was separated from the old shell (OS) after a 16-week rearing period. Mineralogical (aragonite, calcite and dolomite [CaMg(CO 3) 2]) and chemical (Zn, Fe, Mg, Cu and Sr) compositions in both NS and OS were analyzed. Soluble matrix proteins (SMP) were extracted from both OS and NS, followed by amino acid composition analyses. The results showed that mineralogical and chemical compositions in OS were not significantly influenced by dietary zinc. In NS, however, increasing dietary zinc significantly decreased aragonite content, but significantly increased calcite content. Concentrations of Zn and Fe in NS significantly increased with dietary zinc. Patterns of amino acid compositions in NS significantly changed with dietary zinc levels. The ratio of acidic/basic amino acids positively correlated with the ratio of calcite/aragonite in NS.