Chronic copper toxicity of ruminants

Variability of the Ionome of Wild Boar (Sus scrofa) and Red Deer (Cervus elaphus) in a Dutch National Park, with Implications for Biomonitoring

The ionome-an important expression of the physiological state of organisms-is poorly known for mammals. The focus on particular tissues-such as liver, kidney, and bones-in biomonitoring of environmental pollution and potential deficiencies is based on widely held assumptions rather than solid knowledge of full mammalian ionomes. We examined the full ionome of Red deer (Cervus elaphus) and Wild boar (Sus scrofa), two commonly used mammals for biomonitoring, in a Dutch protected nature reserve (Veluwezoom). We used four individuals per species. We dissected 13 tissues and organs from each individuals (eight in total) of each species and measured 22 elemental concentrations in each. We assessed, for each element, how concentrations varied across tissues within and between individuals. Based on existing literature, we put our findings in the context of their function in the mammalian body. We found that the ionome was highly variable between as well as within the two species. For most elements, tissues containing the highest and lowest concentration differed between individuals. No single tissue accurately represented the accumulation of toxic elements or potential deficiencies in the bodies. Our assessment of the element's biological roles revealed a serious lack of reference values. Our findings imply that analyses of commonly used tissues in biomonitoring do not necessarily capture bioaccumulation of toxins or potential deficiencies. We recommend establishing a centralized database of mammalian ionomes to derive reference values in future. To our knowledge, our study is one of the most complete assessments of mammalian ionomes to date.

Safety and efficacy of a molybdenum compound (E7) sodium molybdate dihydrate as feed additive for sheep based on a dossier submitted by Trouw Nutrition International B.V

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on safety and efficacy of sodium molybdate dihydrate for sheep, based on a dossier submitted for the re-evaluation of the additive. The additive is currently authorised in the EU for all animal species as 'Nutritional additive' - 'Compounds of trace elements'. Taking the optimal Cu:Mo ratio of 3-10, and the highest total copper level authorised in complete feeds for sheep (15 mg/kg), the FEEDAP Panel concluded that 2.5 mg total Mo/kg complete feed is safe for sheep. Considering (i) a safe intake of 0.6 mg Mo/day, (ii) the estimate average intake figure from food in Europe (generally less than 100 μg/day), (iii) the contribution of foods of animal origin to the total molybdenum intake (estimated to be up to 22 %), and (iv) that molybdenum would not accumulate in edible tissues/products of sheep fed molybdenum supplemented diets up to the upper safe level, the FEEDAP Panel concluded that the use of sodium molybdate as a additive in sheep at 2.5 mg total Mo/kg complete feed is safe for consumers. The additive under assessment feed poses no risk by inhalation to users; it is a skin and eye irritant, but it is not considered as a skin sensitiser. Sodium molybdate used up to 2.5 mg Mo/kg complete sheep feed poses no concerns for the safety for the environment. The FEEDAP Panel recognises that molybdenum does not need to be added to diets to cover the nutritional needs of molybdenum of sheep. Molybdenum supplementation in sheep feed is considered effective in order to guarantee an adequate balance with copper, when the Cu:Mo ratio in the diet is in the range 3-10.

The distribution of copper, vitamin B12and zinc in the livers of sheep

Six livers from one-year-old sheep were each sampled at 27 different sites and the concentrations of copper, vitamin B12 and zinc determined for each sample. The distribution of these components was uniform throughout the liver, indicating that analysis of a single liver biopsy sample would give an accurate assessment of their hepatic concentration.

A study of protein utilization by weaned lambs

Fifty weaned store lambs approximately 7-month-old were used in an experiment designed to assess their protein requirements and utilization. At the beginning of the experiment a random sample of 10 animals were slaughtered and their loin joints analysed. The remaining 40 were allocated at random to four dietary treatments (T1, T2, T3, T4) comprising four crude protein intakes at a constant energy intake. The experiment was divided into two periods. During period 1 (48 days) the dietary crude protein intakes were 58 (T1), 111 (T2), 170 (T3), and 198 (T4) g/day with a mean digestible organic matter intake (DOMI) of 578 g/day. During period 2 (55 days) the corresponding crude protein intakes were 89, 157, 215, 251 and the DOMI was 678 g/day.

Digestibility and nitrogen balance trials were carried out on two animals from each treatment in period 1 and on six animals on each treatment in period 2. At slaughter the loin joints from five animals on each dietary treatment were chemically analysed.

The only significant effect on live-weight gain of varying protein intake was a lower gain on the lowest protein intake (T1) in period 1. It was estimated that the optimum ratio of digestible protein intake (g) to digestible energy intake (meals) for live-weight gain in period 1 was approximately 30 : 1 and in period 2 approximately 21 : 1. There was a significant increase in killing-out percentage with increasing crude protein intake. The digestibility of dry matter and nitrogen increased with increasing crude protein intake. There was a significant quadratic relationship between the apparently digested nitrogen intake in g/day (X) and nitrogen retained in g/day (Y). The regression equation was

Y= −0·008X2+ 0·537X+ 0·682

Liver copper levels decreased with increasing crude protein con-centration in the diets.

Comparative study of chronic copper poisoning in lambs and young goats

Eighteen lambs (L) and 18 goats (G), 12 weeks of age, were allocated in equal numbers to three diets. The basal (B) diet had no added copper (Cu) while the other two had 30 or 60 mg added Cu per kg dry matter (DM) as CuSO4.5H2O. Lambs and goats were housed and fed individually. After 67 days, deaths from Cu toxicity occurred only in lambs from groups L-30 (basal diet + 30 mg Cu per kg DM) and L-60 (basal diet + 60 mg Cu per kg DM). The remaining lambs and all of the goats were slaughtered at 91 and 137 days respectively.

A decreased food intake and loss of weight were observed in some lambs towards the end of the experiment which appeared to be associated with an approaching haemolytic crisis. The additional dietary Cu had a positive effect on food conversion efficiency only in the early stages of the experiment in both lambs and goats. None of the goats died or lost weight.

Plasma Cu concentrations and serum glutamate oxalacetate transaminase and creatine kinase activities were elevated in lambs of groups L-30 and L-60 after 2 months, while in goats the concentrations were in normal ranges during the whole experimental period.

Additional dietary Cu increased significantly the Cu concentrations of liver, kidney, muscle, spleen, heart, brain, hair and faeces in both lambs and goats. Additional Cu decreased the fresh and dry liver weights of lambs and the liver to live weight ratio whereas the corresponding values for kidneys were increased. The differences between groups of goats in fresh or dry liver and kidney weights were not significant, though the fresh and dry liver weights tended to be higher in groups G·30 and G·60 compared with those in the group G·B.

The amount of Cu stored in the livers of the lambs was six to nine times higher than that of the goats. Differences in Cu storage between lambs and goats may be related to species differences in Cuutilization and hence resistance to Cu toxicity.

High and variable copper status identified among dairy herds in the Waikato region by concentrations of Cu in liver sourced from biopsies and cull cows

AIMS

To document the Cu supplementation practices on dairy farms in the Waikato region, determine the Cu status of those herds, and compare the suitability of liver samples sourced from biopsies and cull cows for assessing Cu status.

METHODS

During spring 2008, concentrations of Cu, Mo and S were determined from pasture samples from 24 dairy farms. Feeding regimens, herd size, milksolids production, soil type, fertiliser policy and Cu supplementation practices were recorded for each property. Based on these data, 10 monitor farms were selected to represent a range of Cu intakes for herds, from 5 to 12 mg Cu/kg dry matter (DM). On each monitor farm 12 healthy lactating cows were selected for liver biopsy and collection of blood samples during the following autumn. Around the same time, livers were collected from 12 cull cows per farm when they were slaughtered, and samples of pasture were again collected from each farm. Concentrations of Cu were measured in all tissue samples.

RESULTS

Concentrations of Cu in pasture tended to be higher (mean 10.4 vs 8.2 mg/kg DM) in the autumn than spring, while concentrations of Mo were lower in the autumn (mean 0.35 vs 1.07 mg/kg DM). Most of the 24 farms used Cu supplementation in some form. Mean concentrations of Cu in liver for herds ranged from 640 (SD 544) to 2,560 (SD 474) micromol/kg fresh tissue in biopsies, and 520 (SD 235) to 2,610 (SD 945) micromol/kg in liver from cull cows. Mean concentrations of Cu in serum ranged from 7.9 to 13.4 micromol/L. The variability in concentrations of Cu for each farm was greater for liver (CV 50%) than serum (CV 21%). For individual cows, concentrations of Cu in liver, obtained by biopsy, and serum were not correlated.

CONCLUSIONS

The concentration of Cu in liver of dairy cows reflected widely differing dietary intakes of Cu between herds, although levels indicated an adequate Cu status on all farms in this study. Use of either biopsy samples or livers from cull cows were indicative of the Cu status of the herd. Wide variation in observed concentrations of Cu in liver indicated that at least 12 cows per herd should be sampled. On farms with intensive, long-term Cu supplementation programmes there is a risk of chronic Cu toxicity in some animals. Thus, the Cu status of dairy herds should be determined, and monitored, before making any recommendations regarding supplementation.

Anaerobic potentiation of copper toxicity and some environmental considerations

The toxicity of copper is substantially greater when the metal ions is applied to cells under conditions of anoxia than under aerobic conditions. The increase in toxicity occurs because Cu(II) is reduced to Cu(I) which is stable under anoxia and is more toxic than the oxidized species. This effect has been observed in mammalian cells in tissue culture and in bacteria. Anoxic potentiation of copper toxicity has also been observed in algal, fungal and yeast cells. The reduction of Cu(II) has been demonstrated by electron paramagnetic resonance spectrometry. The appearance of Cu(I) has been observed by means of specific colorimetric reagent. The reduction of Cu(II) to Cu(I) is not dependent upon concomitant metabolism and requires only a supply of sulphydryl groups. Microorganisms that are responsible for two anaerobic processes of economic importance to humans, the digestion of sewage sludge in effluent treatment plants and the digestion of food in ruminant animals, may be exposed to high concentrations of copper. The environmental consequences of this exposure are discussed.

Copper oxide needles administered during early pregnancy improve the copper status of ewes and their lambs

AIM

To determine the effect of copper oxide (CuO) needles administered orally to ewes in early pregnancy on the copper (Cu) status of ewes throughout gestation and lactation, and of their lambs from birth to weaning.

METHODS

In mid-April, after mating, 12 twin-bearing ewes were given an oral capsule containing 5 g CuO needles while 12 others served as untreated controls. Changes in Cu status were monitored by determining serum and liver Cu concentrations on Days 1, 62, 117, 153, 185 and 216 in the ewes, and at 1, 36, 68 and 99 days of age for lambs. Pasture herbage samples were collected at about 60-day intervals for Cu, molybdenum (Mo), iron (Fe) and sulphur (S) determinations.

RESULTS

Copper status of the ewe flock was adequate, as initial mean serum and liver Cu concentrations were 15 micromol/L and 1,060 micromol/kg fresh tissue, respectively. The CuO needles did not affect serum Cu concentrations of the ewes or their lambs. Mean serum Cu concentration of all lambs at birth was about half that of ewes (8 vs 17 micromol/L), regardless of Cu supplementation, and not until at least 68 days of age was it similar to the dams'. Liver Cu concentrations of lambs at birth were also lower than that of the ewes (380 vs 640 micromol/kg fresh tissue among the controls), but changed little over time. CuO treatment increased liver Cu concentration in ewes for at least 185 days and in lambs for 36 days (p<0.05). Among untreated ewes, there was a seasonal decline in mean liver Cu concentrations, which were highest in autumn and lowest in early spring (1,060 vs 370 micromol/kg fresh tissue). The mean pasture mineral concentrations were Cu 5.7, Mo 0.48, Fe 194 and S 2,900 mg/kg dry matter (DM).

CONCLUSIONS

CuO needles administered to ewes in early pregnancy increased their Cu status through gestation and early lactation, and the Cu status of their lambs for 36 days from birth. Serum Cu concentration was not affected by treatment but a marked rise was observed in all lambs between birth and 10 weeks of age.

CLINICAL RELEVANCE

Copper deficiency in young lambs may be conveniently and effectively prevented by treating ewes with CuO needles during early pregnancy. The serum Cu concentration in lambs <8 weeks old may not reflect the Cu status of the flock.

Investigations into the toxicity of Echium plantagineum in sheep. 2. Pen feeding experiments

In a pen feeding trial fresh Echium plantagineum was fed as the sole diet to crossbred sheep with or without a history of previous access to the plant. Control groups received a diet of lucerne chaff and oats. During the trial, sheep on the Echium diet lost weight and deaths occurred with histological evidence of excessive copper accumulation, usually accompanied by pyrrolizidine alkaloid damage, in the liver and biochemical evidence of liver toxicity. It is concluded that E. plantagineum alone is not a suitable fodder for sheep and can be toxic due to its pyrrolizidine alkaloid content and high copper to molybdenum ratio.

Effect of copper loading of preruminant calves on intracellular distribution of hepatic copper, zinc, iron, and molybdenum

The subcellular distribution of Cu, Zn, Fe, and Mo was investigated in liver homogenates from preruminant calves fed control Cu (10 ppm), high Cu (1000 ppm), or high Cu plus high Zn (1000 ppm) milk replacer. For controls, Cu was located primarily in the nuclei and large granule fractions, Zn mainly in the cytosol, and Fe in the cytosol and nuclei fraction; Mo was present in all compartments but least in microsomes. Calves fed high Cu had markedly increased hepatic Cu concentration in the nuclei and cytosol fractions, reduced cytosol Zn, increased nuclei Fe, and decreased Mo concentration in all cell compartments. Feeding high Zn with high Cu (which prevented deaths from high Cu) reversed some changes in hepatic trace element patterns caused by high Cu while initiating new alterations. The marked increase in hepatic Cu and reduced Mo in nuclei and cytosol after Cu loading indicate that these compartments may have a predominant role in the development of Cu toxicity in the preruminant calf.

Tolerance of the calf for excess copper in milk replacer

Calves were fed milk replacer containing 10, 50, 200, 500, or 1000 ppm Cu, from 3 d to 45 d of age, to estimate the Cu concentration that would adversely affect calf performance. Weight gains and feed efficiency were similar for 10 and 50 ppm Cu but were reduced at 200 and 500 ppm Cu. All calves survived 500 ppm Cu and lower intakes, but only 4 of 7 calves survived the 1000 ppm concentration. Typical clinical symptoms of chronic Cu toxicity and hemolytic crisis were evident for the 1000 ppm calves before death. Additional 1000 ppm Zn prevented deaths for 1000 ppm Cu, but calf performance was poor. Increased Cu intakes elevated plasma ceruloplasmin and glutamic oxalacetic transaminase activity, reduced packed cell volume (hematocrit), markedly increased fecal excretion of Mo and Zn, increased Cu concentration of liver, muscle, heart, blood, and bile, and decreased Mo and Zn in liver. We found 50 ppm Cu a safe intake where milk replacer contained 48 ppm Zn and 1.1 ppm Mo. However, at lower intakes of these elements, and for longer feeding periods than 6 wk, the calf may be much more susceptible to Cu toxicity.

Pyrrolizidine alkaloid poisoning of sheep in New South Wales

Pyrrolizidine alkaloid poisoning of sheep in New South Wales was reviewed, based on the records of the New South Wales Department of Agriculture's Regional Veterinary Laboratories. The plant species causing significant mortalities were Echium plantagineum and Heliotropium europaeum. The syndrome of hepatogenous chronic copper poisoning was more frequently diagnosed than primary pyrrolizidine alkaloid poisoning, particularly when grazing E. plantagineum. The data indicated that adult crossbred ewes were the most commonly affected class of sheep.

Effects of dietary copper supplementation of rats on the occurrence of metallothionein-I in liver and its secretion into blood, bile and urine

The appearance and excretion of metallothionein-I (MT-I) was studied in rats given a diet containing 1000 mg of Cu/kg for several weeks. No significant increase in MT-I concentrations in liver, plasma or bile was detected in rats with liver copper concentrations less than 600 micrograms of Cu/g fresh wt. Above this concentration, liver MT-I concentrations increased in proportion to the increase in hepatic copper content. Plasma and bile MT-I concentrations were directly related to those in the liver and were about 10 times those in normal rats. Urinary MT-I concentration also increased 10-fold within 1 week. Fractionation of bile and urine on Sephadex G-50 revealed the presence of monomeric MT-I and a range of possible degradation products of the isoprotein.

Solubility of copper and zinc containing proteins before and after 2-mercaptoethanol treatment of liver samples from normal and from chronically copper poisoned sheep

The distribution between cytosol and pellet of Cu- and Zn-containing proteins was studied in livers from normal sheep and sheep with chronic copper poisoning (CCP). It was found that the relative amount of soluble Cu- and Zn-containing proteins was lower in liver homogenates from CCP sheep than in homogenates from normal sheep. Treatment of homogenate from the livers of 2-mercaptoethanol (ME) increased the solubility of Cu- and Zn-containing proteins, especially in CCP sheep. Oxidation of the liver homogenates from normal sheep with air oxygen gave a decrease in the relative amount of soluble CU-containing proteins and an increase in Zn-containing proteins present in the cytosol. It is proposed that oxidation in vivo of Cu and/or the metal-binding protein causes the observed decrease in soluble CU- and Zn-containing proteins seen in CCP sheep.

An investigation of the effects of intravenous administration of thiomolybdate on copper metabolism in chronic Cu-poisoned sheep

1. Fourteen sheep were dosed repeatedly with a solution of copper sulphate (2 g/l) in order to induce chronic copper poisoning and four similar undosed animals acted as controls 2. Thiomolybdate (TM) was intravenously administered to all control sheep and to all except two of the test sheep. A variety of biochemical factors were studied before and after injections of TM. 3. The direct-reacting Cu, whole-blood Cu and plasma Cu concentrations were elevated in animals given TM injections and at the "haemolytic crisis" of untreated chronic Cu-poisoned animals. But most of the increased Cu observed on injecting TM was insoluble in trichloroacetic acid (TCA) and did not enter erythrocytes. The results indicate that uptake of Cu by erythrocytes is essential for haemolysis to occur and that for this to happen the Cu must be in a direct reacting, TCA-soluble form. 4. Increased amounts of Cu were excreted in the urine at haemolysis and at commencement of TM injections. High levels of direct-reacting Cu were found in plasma at these times. 5. Marked changes were not found in caeruloplasmin activity, packed cell volume or the osmotic fragility of erythrocytes except at haemolysis. TM injection s did no alter these factors in any of the sheep studied.

Chronic copper poisoning in dairy cows

Chronic copper poisoning in a dairy herd fed supplementary copper is recorded. Most cows received 11 g of copper sulphate per day but high milk producers received 22.0 g and within 6 months, 3 of them became ill and died. The signs shown by the 3 cows were anorexia, decreased milk production, frequent recumbency and jaundice. Within 4 days of showing signs, the cows died. The autopsy findings were dehydration, anaemia, jaundice, liver damage and intestinal haemorrhage. Liver copper values varied from 1,250 to 2,410 ppm DM.

Acute renal failure following copper sulphate intoxication

Eleven out of a series of twenty-nine patients (37-9%) with acute copper sulphate poisoning developed acute renal failure. Intravascular haemolysis appeared to be the chief factor responsible for renal lesions in these patients. Histological lesions observed in the kidney varied from those of mild shock to well established acute tubular necrosis. In one case, granulomatous lesions were seen in response to tubulorrhexis. Renal failure was the chief indication for dialysis in ten patients, whereas one patient was dialysed primarily for removal of copper. Notwithstanding the adequate control of uraemia by dialysis, only six of the eleven patients recovered. Septicaemia was responsible for death in three, hepatic failure in one and methaemoglobinaemia in another. It is postulated that release of copper from haemolysed red cells during acute haemolytic episodes may initiate, or contribute to, the development of renal damage.

Chronic copper poisoning in sheep. ii. The distribution of soluble copper-, molybdenum-, and zinc-binding proteins from liver and kidney

The concentrations of copper, molybdenum, and zinc in the soluble protein fraction from sheep liver and kidney were determined after gel filtration. Samples from grazing sheep as well as from copper poisoned sheep were tested. In normal sheep the copper-binding proteins were separated into 3 different fractions. In copper poisoned sheep, as well as in grazing sheep with high copper concentrations, only 2 main fractions were seen. Molybdenum was only found in the high molecular weight protein fraction. The distribution of the zinc-binding proteins varied according to the degree of copper accumulation. The low molecular weight zinc-binding protein fraction was only seen in sheep with liver copper concentrations lower that 40 mug/g wet weight. In copper poisoned sheep a major part of the kidney copper was found in the low molecular weight protein fraction. At post mortem the bile copper concentrations in the copper poisoned sheep were only 2-4 times higher than those of the control animals.

Protective effect of zinc supplementation against copper toxicosis in sheep

1. A study has been made of the effects of dietary zinc supplementation on the development of copper toxicosis in three groups each of eight 12-week-old lambs. 2. None of the lambs receiving 420 mg Zn/kg diet developed Cu toxicosis in the 24-week experimental period, compared with three in the control group receiving 43 mg Zn/kg and possibly one in the group receiving 220 mg Zn/kg. 3. Liver Cu concentrations were reduced by up to 40% in the Zn-supplemented animals, with concomitant reductions, especially in the early stages of the experiment, in the extent of liver damage, as assessed by measurement of plasma aspartate aminotransferase (EC 2.6.1.1) and arginase (EC 3.5.3.1) activities. 4. Plasma and liver Zn concentrations were increased only slightly in the lambs receiving the Zn-supplemented diets, and the only indication of possible toxic effects of the Zn supplements was the development of a slight anaemia in those animals receiving 420 mg Zn/kg diet. 5. The results suggest that the incidence of Cu toxicosis in sheep may be controlled by increasing their dietary Zn intake.

Heavy metal toxicities

Several reviews have been published recently on the toxicity of heavy metals, but few of these have made any reference to the influence of the nutritional state of animals upon their tolerance of heavy metals. Furthermore, the clinical and metabolic changes occurring as a consequence of increased dietary intake of heavy metals are extremely dependent on factors such as the mineral composition of the diet and nature of the protein source. These aspects will be given particular attention in this review.