Are your cows at risk of copper toxicity?

Copper toxicity is becoming more common in dairy cows and is thought to be an under-diagnosed problem. A UK survey involving 510 cull dairy cattle showed that 40% had liver copper concentrations above the reference range, indicating that they were at a high risk of chronic copper toxicity (Kendall et al, 2015).

Furthermore, a mineral survey of UK dairy herds carried out by Sinclair and Mackenzie (2013) showed that cows in early lactation were being fed on average 154% of copper requirements and 12% of herds exceeded the legal limit.

The main cause of copper toxicity is deliberate excess supplementation.

The problem with copper toxicity is that there are very few warning signs before clinical disease is seen. Although cows suddenly appear to be ill, clinical signs are usually the result of a long process of copper accumulation in the liver, leading to liver degeneration over a period of weeks or even months.

Clinical signs are caused by the sudden release of large amounts of copper into the bloodstream from the liver. This leads to breakdown of red blood cells in the blood vessels causing anaemia, blood in the urine, jaundice, colic and depression. Affected animals will be weak, dull and depressed and have a poor appetite.

Evidence of copper toxicity in cattle with jaundice of the mucous membrane around the eye (left) and liver damage (right – a healthy liver is dark red in colour)

Source: NADIS: https://www.nadis.org.uk/disease-a-z/cattle/chronic-copper-toxicity/

The EU maximum permitted level of copper in cattle rations is 40mg/kg DM and the ACAF (Advisory Committee on Animal Feedstuffs) suggest an industry standard recommendation of 20mg/kg DM. However, some nutritional experts suggest that even 15mg/kg DM is sufficient, especially where cattle are not exposed to high levels of antagonists such as iron, molybdenum and sulphur from forage.

It is very easy to exceed these recommended levels in the diet. According to Thomson and Joseph Ltd, the average copper content from 384 firstt cut grass silages tested in 2019 was 7.4mg/kg DM.

In addition, feeding a mineral supplement with 2000mg/kg of copper at 100g/cow/day provides 200mg of copper. Assuming a herd average dry matter intake of 22kg, this is 9.1mg/kg DM.

This brings the copper intake up to 16.5mg/kg DM from silage and mineral alone, before taking into account any contribution from background levels of other feeds, a mineralised dairy cake or trace element boluses. Draff can also be high in copper if it has come from distilleries with copper stills. Be aware that excess accumulation of copper in the liver can occur over months or years by feeding what is considered a safe level of dietary copper.

Blood tests are not accurate for determining copper status. Accurate assessment of copper status is best carried out by a liver biopsy. This can be done on live or culled animals. If livers test high all supplementary copper should be removed as liver copper concentrations can remain well above deficient levels for very long periods of time (one to two years), even if all copper supplementation is removed.

Calves born to dams high in copper may also be at risk. Copper crosses the placenta into foetal tissues, causing calves to be born with already higher than normal liver copper levels. Furthermore, the absorption of copper in young animals is much greater than in adults and so these calves are more susceptible to liver disease from copper overload and potentially higher mortality rates.

To assess the risk of copper toxicity in your herd, test for liver copper levels in cull cows and carry out a mineral audit with your nutritionist or vet. A forage mineral analysis is essential to determine the overall copper content in the ration so that an appropriate and safe level of supplementary copper can be recommended.

References:

Kendall, N.R., Holmes-Pavord, H.R., Bone, P.A., Ander, E. L. and Young, S. D. 2015. Liver copper concentrations in cull cattle in the UK: are cattle being copper loaded? Veterinary Record 177: 493

Sinclair, L. A. & Mackenzie, A. M. 2013. Mineral nutrition of dairy cows: supply vs. requirements. In Recent Advances in Animal Nutrition (Eds, Garnsworthy, P. C. & Wiseman, J.) pp. 13–30. Ashby de la Zouch, UK: Context Products Ltd.