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The effects of cadmium in feed, and its amelioration with zinc, on element balances in sheep¹

C. J. C. Phillips^*,,2, P. C. Chiy^*, and H. M. Omed

^* Department of Clinical Veterinary Medicine, University of Cambridge, Cambridge CB3 0ES, U.K. and and Department of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, U.K.

	Abstract

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The effects of feeding Cd to sheep at a level that is typical of polluted regions were investigated, as well as possible amelioration by adding Zn to the diet. Welsh Mountain ewes (n = 24) were fed herbage and concentrate in metabolism crates, with four supplement treatments in a two-factor factorial design: no supplement, Cd supplement only, Zn supplement only, and a combination of both the Cd and Zn supplement. Cadmium (286 µg/kg of feed DMI) and Zn (8.6 mg/kg feed DMI) were added as sulfates. Food and water intakes and element balances were recorded over 20 d after 7 d dietary adaptation, and element concentrations were determined in wool samples. Neither metal affected DMI or digestibility (P > 0.15), but water intake (P = 0.001) and urine output (P = 0.03) were decreased when only the Zn supplement was added. Water retention was increased by the Cd supplement (P = 0.04). In wool, the Cd supplement greatly increased the K concentration if no Zn supplement was fed (P = 0.02), and the Zn supplement decreased Mn concentration (P = 0.02). Cadmium in feed increased the Cd balance and produced several mineral disturbances, in particular a decrease in Na balance that is typical of renal tubular disorders. Adding Zn as well as Cd to feed returned the Cd balance to a level similar to that of sheep receiving neither Cd nor Zn, which suggests that Zn status is critical in determining whether Cd in feed increases the Cd balance in sheep. Feeding Cd also increased urinary K, Fe, Mo, Cr, B, and Ca concentrations, even when supplementary Zn was fed. It is concluded that low levels of Cd in sheep feed can increase the Cd balance if adequate Zn is not provided, which can lead to subclinical mineral disturbances and changes in the mineral concentrations in wool.

Key Words: Absorption • Cadmium • Sheep • Toxicity • Wool • Zinc

	Introduction

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Cadmium is a hazardous heavy metal and is a risk to sheep on pasture to which P (Johnston and Jones, 1995) or sewage sludge (Wilkinson et al., 2002) has been applied. Its toxicity in sheep depends on their ability to sequester the Cd with metallothioneins, which are produced in response to Cd, Zn, and Cu (Henry et al., 1994).

Cadmium and Zn have similar properties, and Zn may ameliorate the effects of Cd toxicity in the gastrointestinal and hepatic systems (Prasad, 1983). Much research on the toxic effects of Cd on animals has used provocative levels, often injected, that bear little relationship to farm situations but that do establish the range of possible effects. Little or no research has examined the effects on sheep production and wool quality of moderate pasture contamination with Cd.

Interactions between these two elements are especially important during absorption. Although in rats Cd absorption seems independent of Zn status (Foulkes and Voner, 1981), in sheep dietary Cd increases Zn accumulation, perhaps by stimulating metallothionein production (Doyle and Pfander, 1975; Lee et al., 1994). A simple competitive mechanism is unlikely, partly because the absorption of Zn, but not Cd, is dependent on body mineral status (Foulkes, 1984). Further study is required to determine the interactions between these two elements in sheep fed low levels of Cd.

Many experiments have relied on measuring the Cd in target organs, principally the kidney, to estimate body retention, but estimates of the proportion of Cd metallothionein absorbed by the kidney vary widely, from 41 to 95% (Cain and Griffiths, 1980 and Nordberg and Nordberg, 1975, respectively). We therefore investigated the effects of Cd and Zn supplements on element absorption from the gastrointestinal tract, balances, and blood and wool concentrations, in an attempt to determine whether the provision of Zn supplements would be beneficial in Cd-polluted regions.

	Material and Methods

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Twenty-four barren, adult Welsh Mountain ewes of mean weight 44.8 kg (SE = 0.89) were acclimatized for 15 d to metabolism crates where feed intake and fecal and urinary output could be separately recorded (Vera, 1985). The steel crates were painted and the aluminum excreta separators covered in plastic film to prevent contamination of excreta samples.

A randomized block design with a 2 x 2 factorial arrangement of treatments was used, with sheep allocated to blocks of four animals of similar intake and live weight. Each block was divided at random so that one half of the sheep were allocated to receive a supplement of Cd (Cd₁)—the other half receiving no supplement (Cd₀)—and half of each Cd treatment group received a supplement of zinc (Zn₁), the other half receiving no zinc (Zn₀). The duration of the experiment was 27 d, consisting of a period of adaptation to the diet of 7 d (October 6 through 12) and a measurement period of 20 d (October 13 to November 2).

Ewes were fed fresh cut perennial ryegrass herbage ad libitum and 200 g of concentrate per day (as fed). The herbage was cut daily with a plot forage harvester (Haldrup U.K. Ltd., U.K.) and offered twice daily at 0900 and 1600. A concentrate (Goldenblend Sheep, Frankland Feeds Ltd., Camarthen, U.K.) was used as the carrier for the Cd and Zn supplements (Table 1). Cadmium was fed as CdSO₄•8H₂O (Sigma-Aldrich Co. Ltd., Dorset, U.K.), at a rate of 286 µg of Cd per kilogram of total feed DMI (a typical level in contaminated herbage). Zinc was fed as ZnSO₄•7H₂O (99% purity; Sigma-Aldrich Co. Ltd.), at a rate of 8.6 mg of Zn per kilogram of total feed DMI. This level was chosen after a review of the range of Zn concentrations in typical ruminant diets. Both salts were dissolved in 250 mL of distilled water/(sheep•day), which was mixed with the concentrate allocation for each animal prior to feeding. The same volume of water was added to the concentrate allocation of sheep that did not receive the Cd or zinc supplement. Measurements of the mass of refused herbage, water, feces, and urine were made daily.

	Statistical Analysis

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For element output and balances, a multivariate analysis of variance was initially performed using Wilks’ lambda test (Minitab, 1995) because of the risk of obtaining spurious treatment effects with the large number of analyses being performed on the different elements. The significance of treatment effects was then examined by a mixed complete factorial analysis (2 [Zn] x 2 [Cd] x [six blocks x two periods x 10 d x 24 ewes]), as described by Zolman (1993), using SAS procedures (SAS Inst. Inc., Cary, NC). Statistical estimation and testing procedures were conducted as an unrestricted mixed effect model:

where Y_ijkl(ijk) was the element response; µ the overall mean, and ß the main and interaction effects corresponding to the following factorial levels: ith (Zn), jth (Cd), and kth (sampling days). The term l(ijk) was used for the number of sheep (replicates) within each treatment combination and _m(ijkl(ijk)) was the overall residual error term, normally distributed with mean zero and variance = ². Both ß_l(ijk) and _m[ijkl(ijk)] were random effects used for computing the F-test statistic from main/two-factor interactions and the three-way interaction. The terms ß_il(ijk) + ß_kl(ijk) + ß_ikl(ijk) + ß_jkl(ijk) + ß_ijkl(ijk) were therefore also random. Least square means and associated statistics derived from this model are presented. There were no significant effects of period or day within period, so results are presented for main effects and their interactions only.

Blood data were analyzed in two stages. In Stage 1, an analysis of variance (ANOVA) was conducted with Cd, Zn, and date of blood sampling as treatment factors. In view of the large number of analyses conducted and the paucity of significant treatment effects, stepwise covariance analyses were used in a second stage to elucidate the effects on elements where the significance was borderline, acknowledging that elements interact and could alter treatment effects. Element concentrations were included in an ANOVA model as continuously varying covariates with both Cd and Zn supplementation analyzed as ordinal values and sampling dates treated as a continuous variable. A mixed (forward and backward) stepwise covariance procedure was followed with a probability of 0.25 used as qualification criteria for variates to enter and 0.10 for variates to leave the model. Stepwise covariance equations and least squares means for those treatment effects that were significantly altered by including the listed covariates are presented. The coefficient of determination (R²) presented was adjusted by the following formula: 1 – [residual sums of squares/(n – p)]/[total sums of squares/(n – 1)], where n is the number of replicates and p is the number of coefficient fits in the regression equation. This adjustment was necessary to make it comparable with models containing a different number of predictor parameters.

	Results

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Total DMI was not affected by the Cd or Zn treatments (Table 3). Water intake was reduced when Zn, but not Cd, was added to the diet, compared with the other three treatments (P < 0.001). Despite the changes in water intake that were due to treatment, there were no significant differences in element intake, apart from the expected differences in Zn and Cd intake (P 0.001). This was due to the much lower concentration of elements in water compared with herbage and concentrate.

The multivariate analyses of variances showed that Cd significantly affected overall element output in feces (Wilks’ lambda = 0.025, P = 0.02), but not the overall fecal mineral concentration (Wilks’ lambda = 0.080, P = 0.17). There was a significant interaction between Zn and Cd on element apparent gastrointestinal retention (Wilks’ lambda = 0.035, P = 0.04).

Univariate statistical analyses and associated treatment means of fecal element concentrations are shown in Table 6. The K concentration was decreased by Cd (P = 0.003) and increased by Zn (P = 0.03), and the Mo concentration was greatest when neither Zn nor Cd were added to the diet (P < 0.01). The Cd concentration was increased when Cd was added and this increase was greater if Zn was also added (P < 0.01).

Multivariate analyses of variances showed that the Cd supplement significantly affected element concentrations in urine (Wilks’ lambda = 0.030, P = 0.009) and tended to increase overall urinary element output (Wilks’ lambda = 0.052, P = 0.08). Zinc did not significantly affect overall element concentration in urine (Wilks’ lambda = 0.159, P = 0.34), but it modified the effects of Cd (Wilks’ lambda = 0.062, P = 0.047).

Univariate statistical analyses and associated treatment means of urine element concentrations are given in Table 9. The Cd supplement increased the concentration of Cd in urine and the Zn supplement reduced it, particularly if Cd was also fed (P < 0.03). Feeding Cd increased urinary Na (P = 0.03), K (P = 0.03), Fe (P < 0.01), Mo (P < 0.001), Cr (P = 0.04), B (P = 0.03), and tended to increase Ca (P = 0.07) concentration; it decreased urinary P (P = 0.03) and Zn (P = 0.05) concentration. These effects were not modified by the Zn supplement, which decreased Cu (P = 0.03) and Pb (P = 0.01) and tended to increase urine P concentration (P = 0.09). Zinc supplement also increased Zn in urine, but only when no Cd was added. For Mn, Co, and Ni, the highest concentrations were observed when Cd but no Zn was added (P = 0.03 to 0.04). Neither the Cd nor Zn supplements had any effect on urine Mg and Al concentrations.

The number of plasma and cell samples for each metal below the detection limit of each instrument are tabulated, together with the detection limit for each metal (Table 12). Most of the measured plasma samples with an Al and Ni concentration above the inductively coupled plasma spectrometry detection limit were recorded in the last sampling. Concentrations of Mn, Co, Mo, Cr, and Cd in plasma are not presented because, as well as a significant proportion being below the detection limit, concentrations in the remainder were highly variable and unsuitable for statistical analysis. For the same reason, the intracellular concentrations of Mn, Co, Mo, Cr, Al, B, and Ni are not presented.

Significance of Covariation Between Treatments in Blood Samples

Magnesium. The variation in intracellular Mg concentration was described by intracellular Na and the associated interactions between Cd, Zn, and sampling day:

When the predictor variables were entered as covariates, the sampling day x Zn x Cd treatment was more significant (P < 0.01), compared with P = 0.04 without correction for correlated predictor variables. Treatment Cd₁ increased intracellular Mg by 20% (least squares mean = 11.9 ± 0.42 vs. 14.4 ± 0.43 for Cd₀, s.e.d. = 0.42, P = 0.01). This increase was significantly greater (s.e.d. = 0.557, P = 0.006) in Zn₀ (11.9 ± 0.41 vs. 14.4 ± 0.42) than Zn₁ (12.0 ± 0.54 vs. 13.7 ± 0.53).

Calcium. As well as Cd treatment, the intracellular Ca concentration was significantly affected by intracellular Cu, Na and K concentrations and tended to be affected by intracellular Fe concentration:

When the effects of these elements were entered as covariates, the Cd supplement significantly increased intracellular Ca (least squares mean = 69.5 + 2.0 vs. 62.2 ± 2.14 for Cd₀, s.e.d. = 2.41 mg Ca/L, P = 0.03), which is equivalent to 7.33 (±1.38) mg of Ca per milligram of increase in dietary Cd per kilogram of DM.

Iron. The response of intracellular Fe to Cd supplementation was dependent on intracellular Zn and Cd concentrations, which were themselves mutually antagonistic:

Both Cd and Zn were negatively correlated with intracellular Fe. However, when these effects were controlled for by covariates, the Cd supplement tended to increase blood Fe (least squares means = 1.42 ± 0.138 vs. 1.05 ± 0.148 for Cd₀, s.e.d. = 0.188 mg Cd/L, P = 0.09).

	Discussion

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Digestibility and Growth

The lack of effect of Cd on DM digestibility supports previous research that found little effect of adding large quantities of Cd to the diet of sheep on the extent of rumen bacterial fermentation, although there were adverse effects on protozoan populations (Sviatko and Zelenak, 1993). The increase in ewe weight when Cd was fed without Zn (approximately 700 g) is unlikely to be due to increased digestive efficiency. It may reflect the fact that Cd in restricted doses can increase the weight of affected organs, in particular the kidney, liver, and spleen (Yamano et al., 1998). The kidney, for example, can increase in weight by 25 to 65%, depending on the Cd dose (Bonner et al., 1979), and, if liver and spleen weights were increased by a similar proportion, this could account for the increase in ewe weight. The increase in water balance with Cd may reflect organ hypertrophy and is supported by evidence of the replacement of bone matrix by water in Cd-loaded rats (Brzoska et al., 2001). An alternative hypothesis is that the rate of throughput of digesta was reduced, which is supported by the decreased fecal output in ewes given the Cd supplement. The reported effects of Cd on animal weight gain are variable, with some studies reporting weight loss (Pleasants et al., 1992; Yamano et al., 1998), many no effect (Lafuente et al., 1997; Oishi et al., 2000; Uriu et al., 2000; Reeves and Chaney, 2001), and one suggesting weight gain (Karmakar et al., 1999). Longer term experiments are needed if the effects on ewe weight gain are to be examined in detail. The absence of effect on live weight gain of Cd when Zn was fed supports evidence that Zn protects against Cd toxicity, which was also apparent from the element profile in urine.

The decrease in water intake when Zn but not Cd was added to the diet may relate to observations in laboratory rats (De Castro et al., 1996; Fregoneze et al., 1999) that injected Zn is able to reduce water intake by altering the functional integrity of the angiotensinergic system.

Wool

The absence of any effect of Cd or Zn intake on Cd concentration in wool was expected. Keratin in wool has a low affinity for Cd (Masri and Friedman, 1974), and the rapid removal of ingested Cd from blood probably restricts its uptake by wool follicles. Although Cd concentration is elevated in the wool and hair of animals grazing in polluted areas, such as near a major road (Ward and Savage, 1994) or in an industrial area (Kolacz et al., 1999), in feeding experiments with sheep, no significant transfer of Cd into wool has been observed (Sviatko and Zelenak, 1993). The elevated concentrations in polluted regions are therefore probably the result of surface contamination, and the concentrations of Cd in wool observed in our experiment were similar to control sheep in the experiment of Kolacz et al. (1999).

The dietary Zn concentration of Zn₀ sheep (47 mg/kg DM) was in excess of the requirement for sheep (15 to 20 mg/kg DM [White, 1993]) and the increase to 52 mg/kg DM in Zn₁ sheep would not be expected to affect wool production. However, Zn may have been deficient before the start of the experiment because the plasma Zn concentration was subnormal at the first sampling (Ott et al., 1964). The tendency for a reduction in Zn concentration in wool when Zn and Cd supplements were fed together is possibly due to the increase in calcium status of the ewes when Cd was fed. In humans, Zn concentration in hair is inversely correlated with dietary Ca (Greger and Sciscoe, 1977), and there was a tendency for plasma Zn to be reduced by Cd at the end of the experiment. Alternatively, the large increase in Cu balance when both Zn and Cd were fed as supplements could have decreased Zn uptake into wool. The observation does not agree with a longer (7 mo) study by Sword et al. (1984), who recorded a small (4%) but significant increase in wool Zn in response to an increase in dietary Zn fed to ewes from 23 to 28 mg/kg DM. The latter study may be an exception because no effect of a Zn supplement on hair Zn concentration in cattle was detected by Rojas et al. (1996), and, in humans, Zn concentrations in hair, diet, and plasma are not well correlated (Deeming and Weber, 1978). Any decrease in Zn concentration could have practical implications because Zn induces some resistance to felting shrinkage upon washing if fatty acids are used in the wash water (Masri and Friedman, 1974). No effect on color is likely, but a decrease in flame and insect resistance is expected with reduced Zn concentration (Masri and Friedman, 1974).

The increase in K concentration of wool when Cd was fed as a supplement almost certainly relates to the disturbance that Cd caused in this experiment to the metabolism of those s-block elements of the periodic table (the alkali and alkaline earth metals) that we investigated: Na, K, Mg, and Ca. It decreased the fecal K output and increased the K concentration in urine, although the balance was not affected. Interactions between Cd and K are well established in plants (e.g., Asp et al., 1994), owing in part to the effect of Cd increasing K conductance in cells (Jungwirth et al. 1988). The Cd-induced increase in the K concentration in wool, when no Zn supplement was provided, could cause yellowing of the wool. Potassium salts are the main excretion product of the suint gland. They form a detergent, in association with the relevant anions, that removes the wax layer from the fiber when it is washed by rain. This allows color-forming compounds, such as ammonia and pigments to enter the follicle (Cottle, 1998) and may also make the follicle more susceptible to bacterial attack (Cottle, 1996), regardless of storage (Cottle and Zhao, 1995). It should be noted that the K concentration of wool samples in this experiment was outside the range of samples evaluated by Cottle and Zhao (1995), but this may be a function of preparation method (Aitken et al., 1994). Although the retention of K was not affected by treatment in this experiment, the effects noted for wool and urine concentrations are of sufficient interest to warrant further study of wool parameters, including wool fiber thickness, which also affects K concentration (Taneja et al., 1969).

The decrease in wool Mn concentration when Zn was fed as a supplement was unexpected, as Zn did not affect absorption or retention of Mn. Cadmium as a supplement did, however, significantly increase the Mn balance. A measurement of elemental absorption and retention ignores the complexity of elemental involvement in metabolism, particularly as enzymes, with Zn being involved in over one hundred enzymes in the mammalian body. Critical changes in performance of individual enzymes containing Zn and Mn are likely to go undetected when only element concentrations are measured. One function shared by Mn and Zn is antioxidant activity, with evidence of substitution of Cu-Zn superoxide dismutase (SOD) and MnSOD. Long-term Cu exposure can activate MnSOD (Brouwer and Brouwer, 1998), demonstrating the substitution of Zn-CuSOD and MnSOD as antioxidants, and it is plausible that Zn may do the same. It was not possible to determine whether Zn affected plasma Mn concentration or blood cell Mn concentrations, which were below the detection limits, probably because the Mn is rapidly removed from blood by bones, wool, liver, and other organs where it is used or stored. Manganese was not deficient in the diet, the dietary concentration being considerably in excess of requirements for optimum wool growth (15 to 35 mg/kg DM [Masters et al., 1988]). Another possibility is competition for metallothionein between Mn and Zn. Some studies suggest that Mn has little affinity for metallothionein (Bracken and Klaassen 1987; Sugawara et al., 1994), but others suggest that metallothionein is produced in response to Mn injection (Matsubara et al., 1987). Probably different Mn species stimulate metallothionein production to varying degrees (Fleet et al., 1990); however, excess Zn could also decrease Mn accumulation via glutathione (Liu et al., 1992).

The tendency for Zn to reduce Al in wool may be due to the reaction of both with Fe. Although the Fe balance was not affected by Zn in this experiment, its variance was closely related to that of Al (Chiy et al., 1998), suggesting a connection between the two elements. Iron is well known for its interactions with Zn, leading to anemia at high-Zn intakes. A decrease in Al concentration could have adverse effects on wool quality. Aluminum in wool protects against phototendering of the fibers, a process whereby the tensile strength of the fibers decreases on repeated exposure to light. The metal, in common with chromium, slows the phototendering process, in contrast to Cu and Fe, which induce UV reactivity in keratin, causing weakening of the fibers and yellowing. It has been postulated by Miller and Smith (1995) that the mode of action of Al in this context is to promote intermolecular protein cross-linking via the light-initiated generation of free radicals.

Element Balances

Element accumulation occurs if homeostatic or homeorhetic mechanisms cannot maintain a constant concentration in the body. The absorption of many essential metals is controlled by these mechanisms, such as Zn, whose absorption can vary from less than 10 to over 80% depending on the animal’s status (Underwood and Suttle, 1999). However, mechanisms do not exist for nonessential metals, which were until recently rarely encountered in any significant quantity. Nonessential metals are characterized by low absorption rates unless they utilize absorption mechanisms devised for other metals, e.g., Cd and Zn, and Pb and Ca.

Adding Zn alone to the diet increased the Cd balance to a positive level, which may indicate a metallothionein response to the greatly increased Zn status. Cadmium has a greater affinity for metallothionein than Zn (Squibbs, 1996), and could be retained in greater quantities if the animals have an increased Zn status. When only Cd was added to the diet, the Cd balance was, as expected, strongly positive. However, the Cd balance was negative when both metals were added to the diet, perhaps owing to competition between Cd and Zn for metallothioneins in the intestine (Jaeger, 1990), where they are absorbed. The uptake of Cd and Zn from the intestine is assisted by metallothioneins, which are low–molecular weight, cysteine-rich compounds present in moderate quantities in sheep (Henry et al., 1994). They compete for large ligands, such as serum albumin (Foulkes and Voner, 1981), or those in fiber (Cherian, 1979), which render the metals unabsorbable, at least in monogastrics. Ruminal bacteria can dissociate some large ligands, such as phytic acid, which binds to Zn (Oberleas et al., 1966), and there is evidence for increased absorption of organically bound Zn in ruminants (Spears, 1996).

Cadmium absorption takes place mainly in the proximal small intestine (Pigman et al., 1997), where the metal can damage the microvilli. The transport of Cd into the intestinal mucosal cells probably follows first-order kinetics but may be assisted by low–molecular weight ligands, in particular, metallothioneins, although their presence is not obligatory for transport to take place (Foulkes, 1984). Saturation of the unassisted transport is probably reached at Cd concentrations of 0.01 to 1 mM (Koo et al., 1978; Foulkes, 1984). The transport of Cd from the mucosa to the blood stream is much less than for essential metals, such as Zn, where it may reach 50% (Foulkes, 1984). In an experiment by Valberg et al. (1977), 30% of Cd intake was absorbed by the intestinal mucosa, but as little as 1% entered the body. Cadmium absorbed into mucosal cells, but not transferred to the blood stream, is bound to cell membranes (Taguchi and Suzuki, 1978) and returns to the gastrointestinal tract following the desquamation of these cells. By contrast, Zn is sequestered in intracellular vesicles, the zincosomes (Beyersmann, 2002), and may be released as required, depending on the body burden (Richards and Cousins, 1975).

In our experiment, the Zn balance was increased by Zn the most when both elements were added to the feed. Thus, there was a synergistic effect of feeding Zn and Cd on Zn balance, which may have been due to the sequestration of metallothioneins by Cd, leaving Zn available for metabolic purposes.

Dissociated Cd complexes in the gastrointestinal tract with molybdenum and thiomolybdenates, forming insoluble compounds of low availability (Smith and White, 1997), but the increased gastrointestinal retention of Mo when the Cd supplement was fed in the absence of the Zn supplement would be explained if the Cd compounds were readily dissociated than compounds containing other metals (e.g., Cu). The Cd supplement increased the balance of B, perhaps as a result of greater complexation of Cd with Mo, thus liberating B for absorption. Alternatively, the increased Ca status when the Cd supplement was fed may be related to an increased B balance (Nielsen and Shuler, 1992).

Cadmium decreased the balance of Na, which could indicate reduced Na resorption capabilities by the proximal tubules of the kidney, as observed in Fanconi syndrome following heavy metal toxicity (Kramer et al., 1986). After absorption, Cd is complexed by metallothioneins in the liver and is then removed from the blood stream by the kidney, where it can cause renal failure in excess quantities (Squibbs, 1996). Metallothionein-bound Cd is concentrated in cells bordering the lumen of the proximal tubule and is dissociated by the lysosome system. Only a small amount of the metallothionein (up to 10%) is recycled, and usually nephropathological damage occurs when the metallothionein supply in these cells is insufficient (Squibbs, 1996). Damage to the renal proximal tubule transport system (Fanconi syndrome) is characteristic of chronic Cd toxicity, and this impairs resorption capacity for water and low–molecular weight proteins (Marumo and Li, 1996). In particular, Na-K ATPase activity is inhibited (Kramer et al., 1986) by the production of reactive oxygen species in the proximal tubule, which activate both the proteasomal and endosomal and/or lysosomal proteolytic pathways (Thevonod and Friedmann, 1999). The Na-K ATPase drives reabsorption of ions in the proximal tubule—in particular, Na—hence, the major reduction in Na balance observed in this experiment. Between 30 and 50% of Na is reabsorbed by this mechanism (Jorgensen, 1980), and small doses of Cd decrease the activity of the Na pump to a low level (Thevonod and Friedmann, 1999). Although the cellular activities of Cd during the induction of nephrotoxicity are not well understood, Na-K-ATPase activity is disrupted at micromolar Cd concentrations that would not normally induce Fanconi syndrome (Thevonod and Friedmann, 1999).

Calcium metabolism may be impaired by Cd-induced vitamin D deficiencies (Blainey et al., 1980), which create the brittle bones that are characteristic of humans with the Cd-induced Itai-Itai disease. The Cd supplement increased both the balances of Mg and Ca and the intracellular blood Mg and Ca concentrations. The enhanced Ca status in the intracellular blood fraction may reflect a reduced Ca utilization as a result of vitamin D deficiency.

The balances of Cu, Mn, chromium and lead were also increased by the Cd supplement. In relation to the ultratrace elements, Fanconi syndrome is associated with increases in excretion of some renal glycoproteins (Cvoriscec et al., 1985), abnormalities of which are known to be associated with mineral disturbances, particularly Cu and Zn (Nanto-Salonen et al., 1985). Increased Cu concentrations in the kidneys of rats that ingested Cd-polluted rice have been attributed to metallothionein induction by the Cd, although activity of these elements in metallo-enzymes in a homeostasis disrupted by the Cd cannot be ruled out (Nakagawa et al., 2004). Up-regulation of divalent metal transporter (DMT1) occurs during Cd ingestion and is expressed in the duodenum and the kidney (Leazer et al., 2002). However, the absence of effect of Cd intake on Fe balance in our experiment suggests that this mechanism is not responsible for the increased balance of other cations.

Thus, although there were no signs of clinical toxicity in this experiment, the element balances suggest subclinical disturbances to cation balances similar to those commonly seen in clinical Cd toxicity, but of decreased severity.

	Implications

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Cadmium as a potential pollutant of sheep feed is unlikely to have, in the short term, adverse effects on whole-tract digestion; however, there may be increases in weight as a result of hypertrophy of target organs, such as the kidney and liver. Any elevation of potassium in wool by cadmium supplements may decrease the wool’s natural protection against the development of coloring, especially yellowing. In both cases, the effects of cadmium can be offset by provision of a zinc supplement. A tendency for reduced aluminum concentration in wool when a zinc supplement was fed could enhance phototendering. Our results also demonstrate that levels of cadmium in the diet may produce subclinical disturbances in element balance—in particular, sodium—but also other divalent cations, which are similar in nature to the Fanconi syndrome, but of reduced severity. The zinc status of sheep is likely to be of major importance in determining whether cadmium is toxic.

	Footnotes

 
¹ This study was supported by EU INCO-Copernicus Grant No. CIPA-CT93-0106 and a Turkish Government scholarship for M. Saatci, who assisted in animal management and sample collection. Animal facilities were provided by the Univ. of Wales, Bangor, and chemical analyses were conducted by the Dept. of Analytical Chem., Univ. of Valladolid, Spain. The authors thank J. B. Thomas, J. Pilling, and J. Ffridd for care and handling of the sheep. This work was authorized by the U.K. Home Office under project license No. 40/01219.

² Correspondence: School of Vet. Sci., Univ. of Queensland, Gatton 4343, Australia (phone: 617 33469179; fax: 617 33651255; e-mail: c.phillips{at}uq.edu.au).

Received for publication May 30, 2003. Accepted for publication April 12, 2004.

	Literature Cited

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Aitken, F. J., D. J. Cottle, T. C. Reid, and B. R. Wilkinson. 1994. Mineral and amino-acid composition of wool from New Zealand Merino sheep differing in susceptibility to yellowing. Aust. J. Agric. Res. 45:391–401.

Asp, H., M. Gussarsson, S. Adalsteinsson, and P. Jensen. 1994. Control of potassium influx in roots of birch (Betula Pendula) seedlings exposed to cadmium. J. Exp. Bot. 45:1823–1827.[Abstract/Free Full Text]

Beyersmann, D. 2002. Homeostasis and cellular functions of zinc. Materialwissensch. Werkstofftechn. 33:764–769.

Blainey, J. D., R. G. Adams, D. B. Brewer, and T. C. Harvey. 1980. Cadmium-induced osteomalacia. Br. J. Ind. Med. 37:278–284.[Medline]

Bonner, F. W., L. J. King, and D. V. Parke. 1979. The tissue deposition and urinary excretion of cadmium, zinc, Cu and iron, following repeated parenteral administration of cadmium to rats. Chem.-Biol. Interact. 27:343–351.[Medline]

Bracken, W. M., and C. D. Klaassen. 1987. Induction of metallothionein in rat primary hepatocyte cultures: evidence for direct and indirect induction. J. Toxicol. Environ. Health 22:163–174.[Medline]

Brouwer, M., and T. H. Brouwer. 1998. Biochemical defense mechanisms against copper-induced oxidative damage in the blue crab, Callinectes sapidus. Arch. Biochem. Biophys. 351:257–264.[Medline]

Brzoska, M. M., J. Moniuszko, J. Jakoniuk, M. Jurczuk, M. Galazyn-Sidorczuk, and J. Rogalska. 2001. The effect of zinc supply on cadmium-induced changes in the tibia of rats. Food Chem. Toxicol. 39:729–737.[Medline]

Cain, K., and B. Griffiths. 1980. Transfer of liver cadmium to the kidney after aflatoxin induced liver damage. Biochem. Pharmacol. 29:1852–1855.[Medline]

Cherian, M. G. 1979. Metabolism of orally-administered cadmium-metallothionein in mice. Environ. Health Persp. 28:127–130.[Medline]

Chiy, P. C., M. de la Fuente, E. Barrado, M. Vega, and C. J. C. Phillips. 1998. The determination of mineral balances in sheep offered feed with added cadmium and zinc. Fresenius’ J. Anal. Chem. 361:343–348.

Cottle, D. J. 1996. Selection programs for fleece rot resistance in Merino sheep. Aust. J. Agric. Res. 47:1213–1233.

Cottle, D. J. 1998. Changes in wool color—Part II: Dumping and storage. J. Textile Inst. 89:10–25.

Cottle, D. J., and W. Zhao. 1995. Changes in wool color: 1. Incubation of wool to promote a more stable wool color. J. Textile Inst. 86:136–147.

Cvoriscec, D., A. Stavljenic, and M. Radonic. 1985. Tamm-Horsfall protein in Balkan endemic nephropathy. J. Clin. Chem. Clin. Biochem. 23:177–181.[Medline]

De Castro, E., E. Silva, H. Ferreira, M. Cunha, C. Bulcao, C. Sarmento, I. De Oliveira, and J. B. Fregoneze. 1996. Effect of central acute administration of cadmium on drinking behavior. Pharmacol. Biochem. Behav. 53:687–693.[Medline]

Deeming, S. B., and C. W. Weber. 1978. Hair analysis of trace minerals in human subjects as influenced by age, sex, and contraceptive drugs. Am. J. Clin. Nutr. 31:1175–1180.[Abstract/Free Full Text]

Doyle, J. J., and W. H. Pfander. 1975. Interactions of cadmium with copper, iron, zinc and manganese in ovine tissues. J. Nutr. 105:599–606.

Fleet, J. C., K. A. Golemboski, R. R. Dietert, G. K. Andrews, and C. C. McCormick. 1990. Induction of hepatic metallothionein by intraperitoneal metal injection: An associated inflammatory response. Am. J. Physiol. Gastrointest. Liver Physiol. 258:G926–G933.[Abstract/Free Full Text]

Foulkes, E. C. 1984. Intestinal absorption of heavy metals. Pages 543–565 in Pharmacology of Intestinal Permeation. T. Z. Csáky, ed. Springer Verlag, Berlin.

Foulkes, E. C., and C. Voner. 1981. Effects of Zn status, bile and other endogenous factors on jejunal Cd absorption. Toxicology 22:115–122.[Medline]

Fregoneze, J. B., C. P. Luz, L. Castro, P. Oliveira, A. K. Lima, F. Souza, I. Maldonado, D. F. Macedo, M. G. Ferreira, I. P. Bandeira, M. A. Rocha, F. L. Carvalho, E. D. Castro, and E. Silva. 1999. Zinc and water intake in rats: investigation of adrenergic and opiatergic central mechanisms. Braz. J. Med. Biol. Res. 32:1217–1222.[Medline]

Greger, J. L., and B. S. Sciscoe. 1977. Zinc nutriture of elderly participants in an urban feeding program. J. Am. Diet. Assoc. 70:37–41.[Medline]

Griepink, B., and H. Muntau. 1988. The certification of the contents (mass fractions) of As, B, Cd, Hg, Mn, Mo, Ni, Pb, Sb, Se and Zn in ryegrass. Commission of the European Communities. Report EUR 11839 EN.

Henry, R. B., J. Liu, S. Choudhuri, and C. D. Klassen. 1994. Species variation in hepatic metallothionein. Toxicol. Lett. (Shannon) 74:23–33.

Jaeger, D. E. 1990. Absorption interactions of zinc and cadmium in the isolated perfused rat intestine. J. Trace Elem. Electrolytes Health Dis. 4:101–105.[Medline]

Johnston, A. E., and K. C. Jones. 1995. Pages 6–8 in the Origin and Fate of Cadmium in Soil. Proc. No. 366. The Fertiliser Society, Peterborough, UK.

Jorgensen, P. L. 1980. The sodium and potassium ion pump in kidney tubules. Phys. Rev. 60:864–907.[Free Full Text]

Jungwirth, A., M. Paulmichl, and F. Lang. 1988. Enhancement of cell membrane potassium conductance by cadmium and mercury ions. Biol. Chem. Hoppe-Seyler 369:845.

Karmakar, R., S. Roy, and M. Chatterjee. 1999. The effects of cadmium on the hepatic and renal levels of reduced glutathione, the activity of glutathione S. transferase and gamma glutamyl transpeptidase. J. Environ. Pathol. Toxicol. Oncol. 18:29–35.[Medline]

Kolacz, R., E. Bodak, Z. Dobrzanski, and B. Patkowska-Sokola. 1999. Trace elements in the wool of Polish merino sheep grazed in polluted and unpolluted environment. Czech J. Anim. Sci. 44:509–514.

Koo, S. I., C. S. Fullmer, and R. H. Wasserman. 1978. Intestinal absorption and retention of 109 Cd: Effects of cholecalciferol, calcium status and other variables. J. Nutr. 108:1812–1822.

Kramer, H. J., H. C. Gonick, and E. Lu. 1986. In vitro inhibition of Na-K-ATPase by trace metals: Relation to renal and cardiovascular damage. Nephron 44:329–336.[Medline]

Lafuente, A., A. Blanco, N. Marquez, E. Alvarez-Demanuel, and A. I. Esquifino. 1997. Effects of acute and subchronic cadmium administration on pituitary hormone secretion in rat. Rev. Esp. Fisiol. 53:265–269.[Medline]

Leazer, T. M., Y. P. Liu, and C. D. Klaassen. 2002. Cadmium absorption and its relationship to divalent metal transporter-1 in the pregnant rat. Toxicol. Appl. Pharmacol. 185:18–24.[Medline]

Lee, J., B. P. Trefloar, and N. D. Grace. 1994. Metallothionein and trace element metabolism in sheep tissues in response to high and sustained zinc dosages. 2. Expression of metallothionein m-RNA. Aust. J. Agric. Res. 45:321–332.

Liu, J., W. C. Kershaw, and C. D. Klaassen. 1992. Protective effects of zinc on cultured rat primary hepatocytes to metals with low affinity for metallothionein. J. Toxicol. Environ. Health. 35:51–62.[Medline]

Marumo, F., and J. P. Li. 1996. Renal disease and trace elements [in Japanese]. Nippon Rinsho. 54:93–98.[Medline]

Masri, M. S., and M. Friedman. 1974. Interactions of keratins with metal ions: uptake profiles, mode of binding, and effects on properties of wool. Adv. Exp. Med. Biol. 48:551–587.[Medline]

Masters, D. G., D. I. Paynter, J. Briegel, S. K. Baker, and D. B. Purser. 1988. Influence of manganese intake on body, wool and testicular growth of young rams and on the concentration of manganese and the activity of manganese enzymes in tissues. Aust J. Agric. Res. 39:517–524.

Matsubara, J., Y. Tajima, and M. Karasawa. 1987. Metallothioneinu induction as a potent means of radiation protection in mice. Radiat. Res. 111:267–275.[Medline]

Miller, I. J., and G. J. Smith. 1995. Protection against phototendering of wool by metal salts and mordanted dyes. J. Soc. Dyers Colourists 111:103–106.

Minitab. 1995. Minitab Reference Manual, Release 10Xtra for Windows and Macintosh. Minitab Inc., State College, PA.

Nakagawa, J., S. Oishi, J. Suzuki, Y. Tsuchiya, M. Ando, and Y. Fujimoto. 2004. Effects of long-term ingestion of cadmium-polluted rice or low-dose cadmium-supplemented diet on the endogenous copper and zinc balance in female rats. J. Health Sci. 50:92–96.

Nanto-Salonen, K., T. Halme, R. Penttinen, F. V. Langevelde, R. D. Vis, and G. Alfthan. 1985. Disturbed metabolism of copper and zinc in aspartylglycosaminuria: Possible involvement with connective tissue changes. J. Inherit. Metab. Dis. 8:212–218.[Medline]

Nielsen, F. H., and T. R. Shuler. 1992. Studies of the interaction between boron and calcium, and its modification by magnesium and potassium, in rats. Effects on growth, blood variables, and bone mineral composition. Biol. Trace Elem. Res. 35:225–237.[Medline]

Nordberg, M., and G. F. Nordberg. 1975. Distribution of metallothionein-bound cadmium and cadmium chloride in mice: preliminary studies. Environ. Health Persp. 12:103–108.[Medline]

Oberleas, D., M. Muhrer, and B. L. Odell. 1966. Dietary metal-complexing agents and zinc availability in the rat. J. Nutr. 90:56–62.

Oishi, S., J. Nakagawa, and M. Ando. 2000. Effects of cadmium administration on the endogenous metal balance in rats. Biol. Trace Elem. Res. 76:257–278.[Medline]

Ott, E. A., W. H. Smith, M. Stob, and W. M. Beeson. 1964. Zinc deficiency syndrome in young lamb. J. Nutr. 82:41–50.

Pigman, E. A., J. Blanchard, and H. E. Laird. 1997. A study of cadmium transport pathways using the Caco-2 cell model. Toxicol. Appl. Pharmacol. 142:243–247.[Medline]

Pleasants, E. W., M. E. Sandow, S. Decandido, B. S. C. Waslien, and B. A. Naughton. 1992. The effect of vitamin D3 and 1, 25-dihydroxyvitamin D3 on the toxic symptoms of cadmium exposed rats. Nutr. Res. 12:1393–1403.

Prasad, A. S. 1983. The role of zinc in gastrointestinal and liver disease. Clin. Gastroent. 12:713–741.

Reeves, P. G., and R. L. Chaney. 2001. Mineral status of female rats affects the absorption and organ distribution of dietary cadmium derived from edible sunflower kernels (Helianthus annuus L.). Environ. Res. 85:215–225.[Medline]

Richards, M. P., and R. J. Cousins. 1975. Mammalian zinc homeostasis; Requirement for RNA and metallothionein synthesis. Biochem. Biophys. Res. Commun. 64:1215–1223.[Medline]

Rojas, L. X., L. R. McDowell, F. G. Martin, N. S. Wilkinson, A. B. Johnson, and C. A. Njeru. 1996. Relative bioavailability of zinc methionine and two inorganic zinc sources fed to cattle. J. Trace Elem. Med. Biol. 10:205–209.[Medline]

Smith, G. M., and C. L. White. 1997. A molybdenum-sulfur-cadmium interaction in sheep. Aust. J. Agric. Res. 48:147–154.

Spears, J. W. 1996. Organic trace elements in ruminant nutrition. Anim. Feed Sci. Technol. 58:151–163.

Squibbs, K. S. 1996. Roles of metal-binding proteins in mechanisms of nephrotoxicity of metals. Pages 731–736 in Toxicology of Metals. L. W. Chang, ed. CRC Lewis, London.

Sugawara, N., D. Li, and C. Sugawara. 1994. Biliary excretion of exogenous cadmium and manganese in Long-Evans Cinnamon (LEC) rats characterized by an inherently gross amount of copper-metallothionein in the liver. Arch. Toxicol. 68:520–523.[Medline]

Sviatko, P., and I. Zelenak. 1993. The influence of cadmium on parameters of rumen fermentation and its content in biological materials in sheep. Vet. Med. (Prague) 38:229–235.

Sword, J. T., A. M. Ataja, A. L. Pope, and W. G. Hoekstra. 1984. Effect of calcium phosphates and zinc in salt-mineral on ad libitum salt-mix intake and on zinc and selenium status of sheep. J. Anim. Sci. 59:1594–1600.

Taguchi, T., and S. Suzuki. 1978. Cadmium binding components in the supernatant fraction of the small intestinal mucosa of rats administering cadmium. Jpn. J. Hyg. 33:467–473.

Taneja, G. C., N. L. Narayan, and P. K. Ghosh. 1969. On the relationship between wool quality and the type and concentration of blood potassium in sheep. Experientia 25:1200–1201.[Medline]

Thevonod, F., and J. M. Friedmann. 1999. Cadmium-mediated oxidative stress in kidney proximal tubule cells induces degradation of Na+/K+-ATPase through proteasomal and endo-/lysosomal proteolytic pathways. FASEB J. 13:1751–1761.[Abstract/Free Full Text]

Underwood, E. J., and N. F. Suttle. 1999. The Mineral Nutrition of Livestock. CABI, Wallingford, U.K.

NRC. 1982. United States-Canadian Tables of Feed Composition: Nutritional Data for United States and Canadian Feeds, Third Revision Subcommittee on Feed Composition, Committee on Animal Nutrition, National Research Council National Academies Press, Washington, DC.

Uriu, K., K. Kaizu, Y. L. Qie, A. Ito, I. Takagi, K. Suzuka, Y. Inada, O. Hashimoto, and S. Eto. 2000. Long. term oral intake of low-dose cadmium exacerbates age-related impairment of renal functional reserve in rats. Toxicol. Appl. Pharmacol. 169:151–158.[Medline]

Valberg, L. S., J. Haist, and M. G. Cherian. 1977. Cadmium-induced enteropathy: comparative toxicity of cadmium chloride and cadmium-thionein. J. Toxicol. Environ. Health 2:963–975.[Medline]

Vera, A. J. 1985. Studies on the digestion of conserved forages in sheep. Ph.D. Thesis, Univ. Wales, Bangor, U.K.

Wagstaffe, P. J., B. Griepink, H. Hecht, H. Muntau, and P. Schramel. 1988. The certification of the contents (mass fractions) of Cd, Pb, As, Hg, Se, Cu, Zn, Fe and Mn in three lyophilised animal tissue reference materials. Commission of the European Communities. Report EUR 10618 EN.

Ward, N. I., and J. M. Savage. 1994. Elemental status of grazing animals located adjacent to the London orbital (M25) motorway. Sci. Total Environ. 147:185–189.

White, C. L. 1993. The zinc requirements of grazing ruminants. Pages 197–206 in Zinc in Soils and Plants: Developments in Plant and Soil Sciences, Vol. 55. A. D. Robson, ed. Kluwer Academic Publishers, London.

Wilkinson, J. M., J. Hill, and C. T. Livesey. 2002. The accumulation of potentially toxic elements in the body tissues of sheep grazed on grassland given repeated applications of sewage sludge. Anim. Sci. (Pencaitland) 72:179–190.

Yamano, T., M. Shimizu, and T. Noda. 1998. Comparative effects of repeated administration of cadmium on kidney, spleen, thymus, and bone marrow in 2-, 4-, and 8-month old male Wistar rats. Toxicol. Sci. 46:393–402.[Abstract/Free Full Text]

Zolman, J. F. 1993. Biostatistics: Experimental Design and Statistical Inference. Oxford University Press, New York.

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