The role of liver Cu kinetics in the depletion of reserves of Cu in dairy cows fed a Cu-deficient diet

Copper Supplementation, A Challenge in Cattle

Ensuring adequate copper supplementation in ruminants is a challenging task due to the complexity of copper metabolism in these animals. The three-way interaction between copper, molybdenum and sulphur (Cu-Mo-S) in the rumen makes ruminants, particularly cattle, very susceptible to suffering from secondary copper deficiency. Paradoxically, excessive copper storage in the liver to prevent deficiency becomes a hazard when ruminants are fed copper-supplemented diets even slightly above requirements. While cattle were traditionally thought to be relatively tolerant of copper accumulation, and reports of copper poisoning were until recently somewhat rare, in recent years an increased number of episodes/outbreaks of copper toxicity in cattle, particularly in dairy cattle, have been reported worldwide. The growing number of lethal cases reported seems to indicate that copper intoxication is spreading silently in dairy herds, urging the development of strategies to monitor herd copper status and improve farmers' awareness of copper toxicity. In fact, monitoring studies carried out on numerous samples collected from culled animals in slaughterhouses and/or diagnostic laboratories have demonstrated that large numbers of animals have hepatic copper concentrations well above adequate levels in many different countries. These trends are undoubtedly due to copper supplementation aimed at preventing copper deficiency, as dietary copper intake from pasture alone is unlikely to cause such high levels of accumulation in liver tissue. The reasons behind the copper overfeeding in cattle are related both to a poor understanding of copper metabolism and the theory of "if adding a little produces a response, then adding a lot will produce a better response". Contrary to most trace elements, copper in ruminants has narrow margins of safety, which must also be formulated considering the concentrations of copper antagonists in the diet. This review paper aims to provide nutritionists/veterinary practitioners with the key points about copper metabolism in cattle to guarantee an adequate copper supply while preventing excessive hepatic copper loading, which requires à la carte copper supplementation for each herd.

Effect of sodium molybdate supplementation on high concentrations of Cu in liver of yearling bulls

AIM

To determine the impact of sodium molybdate treatment, given weekly, on concentrations of Cu in liver, activity of liver enzymes, and weight gain over 4 weeks, in yearling bulls with elevated concentrations of Cu in liver.

METHODS

The study was carried on two commercial grazing farms in the Otago region of New Zealand in yearling Friesian bulls (n=150 on Farm A and n=49 on Farm B) with mean concentration of Cu in liver >3,000 µmol/kg fresh weight. On Day 0, all animals were weighed and half were systematically allocated to treatment with sodium molybdate (3 mg/kg liveweight on Farm A and 7 mg/kg liveweight on Farm B); the remainder received no treatment (Control). Sodium molybdate was given as a drench weekly for 4 weeks and all animals were weighed again on Day 28. Ten animals on each farm (five from each treatment group) were systematically selected for blood sampling and liver biopsies on Days 0 and 28. Samples were analysed for concentrations of Cu in plasma, vitamin B₁₂ in serum, activities of γ-glutamyl transferase, aspartate aminotransferase and glutamate dehydrogenase in serum, and concentrations of Cu and vitamin B₁₂ in liver. Separate multivariable linear models were used to compare the change in outcome variables between Days 0 and 28 between bulls that had been drenched with sodium molybdate or not.

RESULTS

On Farm A, mean concentrations of Cu in liver on Day 28, as a percentage of concentrations on Day 0, for the control group was 55 (95% CI=40-73)% and for the treatment group was 73 (95% CI=43-111)%. On Farm B, the equivalent mean for the control group was 75 (95% CI=42-131)% and for the treatment group was 85 (95% CI=38-134)%. The multivariable linear models indicated that the changes in concentrations of Cu in liver, activities of liver enzymes and weight gain between Days 0 and 28 did not differ between the bulls treated or not with sodium molybdate (p>0.18).

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment with sodium molybdate in one bolus at weekly intervals for 4 weeks did not affect concentrations of Cu in liver, activity of liver enzymes or weight gain in animals with high concentrations of Cu liver on two farms.

Liver copper concentrations in cull cattle in the UK: are cattle being copper loaded?

With the release of the Department for the Environment, Food and Rural Affairs/Advisory Committee on Animal Feed Guidance Note for Supplementing Copper to Bovines it was noted that the current copper status of the national herd was not known. Liver samples were recovered from 510 cull cattle at a single abattoir across a period of three days. The samples were wet-ashed and liver copper concentrations determined by inductively coupled plasma mass spectrometry analysis. Breed, age and previous location information were obtained from the British Cattle Movement Service. Dairy breeds had higher liver copper concentrations than beef breeds. Holstein-Friesian and ‘other’ dairy breeds had 38.3 per cent and 40 per cent of cattle above the Animal Health and Veterinary Laboratories Agency (AHVLA) reference range (8000 µmol/kg dry matter), respectively, whereas only 16.9 per cent of animals in the combined beef breeds exceeded this value. It was found that underlying topsoil copper concentration was not related to liver copper content and that age of the animal also had little effect on liver concentration. In conclusion, over 50 per cent of the liver samples tested had greater-than-normal concentrations of copper with almost 40 per cent of the female dairy cattle having liver copper concentrations above the AHVLA reference range, indicating that a significant proportion of the UK herd is at risk of chronic copper toxicity.

Effects of subcutaneously injected Ca Cu EDTA on concentrations of Cu in liver, milk production and reproductive performance in New Zealand dairy cows

AIMS

To determine the effect of dose and frequency of injection of Cu as Ca Cu EDTA on concentrations of Cu in liver, and the effect of a single 200 mg treatment on milk production and reproductive performance in New Zealand dairy cows.

METHODS

Four groups of dairy cows (n=18 per group) on three farms were injected with 100 or 200 mg Cu S/C once, or three times at 6-weekly intervals, commencing 6-8 weeks into lactation. Concentrations of Cu in liver were determined to 119 days after treatment. Cows at peak lactation on one farm were treated with 200 mg of Cu S/C, or received no treatment (n=92 per group). Milk production was determined 11 days before and 24 hours following treatment. In seven dairy herds from throughout New Zealand cows were injected S/C with 200 mg Cu 10 days prior to mating start date (MSD) or received no treatment. Oestrus detection and artificial inseminations were carried out for ≥ 2 - 4 days from MSD. Pregnancy diagnosis was performed at 12 weeks following MSD. The percentage of cows inseminated in the 21 days after MSD (21-day submission rate; n=2,022) and cows pregnant after 21 or 28 days (21- and 28-day pregnancy rates; n=2520) was determined.

RESULTS

Injecting with 200 mg Cu once or 6-weekly increased concentrations of Cu in liver compared with 100 mg (p<0.05). Injection of 200 mg Cu decreased total milk yield (p=0.006) and protein production (p<0.001) in the 24-36 hours after treatment. Compared with Control cows, 200 mg Cu 10 days before MSD reduced 21-day submission (78 vs. 75%; p=0.04) and 21-day pregnancy rates (47 vs. 43%; p=0.03). For 28-day pregnancy rates there was a farm by treatment interaction (p=0.02), with a negative effect observed on some, but not other, farms.

CONCLUSIONS

Injection of 200 mg Cu raised concentrations of Cu in liver for >42 days. A negative impact on milk yield and composition occurred immediately following injection. Injection 10 days prior to mating had a negative effect on submission and pregnancy rates. Further study is required to determine a safe treatment to mating interval and the mechanism by which adverse impacts occur.

CLINICAL REVELENCE

Although 200 mg of Cu as Ca Cu EDTA is an effective supplement and generally well tolerated, determining the necessity for, and giving specific thought to the timing of, parenteral Cu supplementation is imperative to avoid negative impacts on herd production and reproductive performance.

Using sodium molybdate to treat chronic copper toxicity in dairy cows: A practical approach

Abstract

CASE HISTORY

A Jersey herd of 350 cows and 70 heifers located in the Taranaki region of New Zealand ceased milking in June 2011. Ten cows died during the subsequent 14 days. For at least 9 months, the cows had received palm kernel expeller (PKE) and molasses supplements. Additional Cu supplementation was provided through the water system. Total Cu intake was calculated to be 400 mg/day/cow.

CLINICAL AND PATHOLOGICAL FINDINGS

Half of the cows died suddenly while others presented with anorexia, depression and ataxia, which progressed to recumbency and death after 1 to 3 days. Clinical signs were mild dehydration, cyanosis and firm faeces which were covered in dark blood. Mean concentrations of Cu in liver and kidney in three of the dead cows were 3,900 and 440 µmol/kg fresh weight (FW), respectively. Haemorrhages were observed throughout the alimentary tracts and in muscles, and there were ecchymotic haemorrhages on the epi- and endocardia. The livers were swollen and the gall bladder walls were inflamed.

DIAGNOSIS

High concentrations of Cu in the liver and kidney are characteristic findings of chronic Cu toxicity.

TREATMENT

The remaining herd was fed 200 mg Mo, as sodium molybdate, per cow per day and all Cu supplements were removed including those provided by the water supply. This reduced mean concentrations of Cu in liver from 3,100 to 1,320 µmol/kg FW within 26 days in the five live animals that were biopsied. There were no further deaths.

CLINICAL RELEVANCE

In dairy herds where excessive Cu intakes have resulted in high liver Cu concentrations and caused chronic Cu toxicity, the removal of all Cu supplements and provision of high intakes of Mo (200 mg/cow/day) can markedly reduce liver Cu stores within 4 weeks.