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Copper intake: getting the balance right

Laura Bowyer speaks to professor Liam Sinclair, lecturer at Harper Adams University, about copper poisoning and the best way to avoid copper toxicity through supplementation.
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Sheep and cattle are susceptible to copper poisoning, with reportedly about 30 cattle each year in the UK killed by the toxicity, but it is thought many more cases go unreported or unidentified.


Recent research from University of Nottingham suggested some 40 per cent of dairy cattle have liver copper concentrations exceeding the Animal and Plant Health Agency’s recommendations, compared to just 17 per cent for combined beef breeds.


The reason for these higher levels of copper loading to the liver, is the nature of dairy farming, suggests Prof Liam Sinclair, professor of animal science and senior vice-president of the British Society of Animal Science. He says: “Dairy cattle are often fed more supplements containing copper and are therefore at a higher risk from toxicity. Younger animals can be particularly susceptible, before their rumen fully develops and is much more absorbent, but decreasingly so as it gets older.”

 

Signs

Prof Sinclair warns there are not really any tell-tale signs of an animal having copper poisoning, until shortly before death. The liver can store levels of copper, but when too much of the mineral is present it is rapidly released into the blood stream and can also result in high kidney concentrations.


“Roughly 30 cases of acute liver toxicity are reported annually in the UK, but this is just the tip of the iceberg, many more cases go undetected,” says Prof Sinclair.


“Sometimes an outbreak can happen in a herd, but it is only really a liver biopsy or cull cow test which will diagnose the problem.”


Copper is an interesting mineral, says Prof Sinclair, as insufficient amounts in the diet can result in deficiency, but excess can end in toxicity. Copper can be present in the animal but locked up in the rumen by antagonists, often due to a complex with sulphur and molybdenum. This forms thiomolybdates in the rumen which bind dietary copper, making it unavailable to the animal.


Other minerals such as iron can also add to the binding of copper, preventing the small intestine from absorbing the mineral. He says: “The animal may seem to have a copper deficiency, but they just cannot absorb it. This is what we call a secondary deficiency. Farmers become afraid of having a deficiency in their herd so supply more when it is not needed.


Prof Sinclair says in these conditions the only remedy is to feed more copper, but this is often when the problem arises.


“For most herds in the UK, these antagonists are at low levels, but farmers may not know this and feed excess copper.


“It is only by getting a forage mineral analysis and looking at all dietary ingredients you will determine whether these antagonists are likely to be a problem. Even then, for most farmers the level of copper many feed is not justified.


“Farmers can be easily persuaded to feed more copper to cattle, as the mineral can have positive effects on milk yields, fertility and bone strength.”

Copper concentration in cattle diets

  • Normal recommended dietary concentration of copper – 11mg/kg DM
  • Feed industry maximum recommended concentration – 20mg/kg DM
  • EU legal limit – 40mg/kg DM
  • Mean concentration in 50 herds surveyed by Prof Sinclair in central and northern England – 24mg/kg DM, with six out of the 50 herds feeding above 40mg/kg DM in early lactation

Reducing risk of copper poisoning

Prof Sinclair’s top tips for reducing the risk of copper poisoning:
  • Make one person responsible for mineral nutrition on-farm
  • Analyse your forage throughout winter for minerals
  • Include the contribution from all sources when calculating copper intake (forages, concentrates, free access minerals, boluses) and make sure you are not feeding excess
  • Blood sampling can be useful to diagnose a suspected deficiency, but may not be suitable to determine if excess is being fed. A liver biopsy sample (taken by the vet), or a liver sample from cull cows is more useful
  • Give particular attention to heifers who are more susceptible to toxicity
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