Proposed reductions in the maximum content of copper in feed for piglets, cattle and dairy cattle have been recommended by the European Food Safety Authority (EFSA) in a bid to reduce the amount of copper released into the environment, and potential antimicrobial resistance.

EFSA’s panel on Additives and Products or Substances used in Animal Feed (FEEDAP) recommends that copper content in complete feed for piglets should not exceed 25mg per kg (down from 170mg/kg), with the maximum content of copper in complete feed for dairy cows and cattle being reduced from 35mg/kg of feed to 30mg/kg.

For most other animal groups the currently authorised upper levels are unchanged except for goats where an increase is recommended.

These new levels are considered sufficient to satisfy the nutritional needs for copper of these animal groups, with the reduction of copper in feed for piglets expected to reduce the release of copper into the environment through manure by 20%, while also helping to reduce antimicrobial resistance in pigs and in the environment.

However, while there have been no recommendations proposed to cut copper levels in sheep feed, Agri-Food and Biosciences Institute – an amalgamation of the Department of Agriculture and Rural Development (DARD) Science Service and the Agricultural Research Institute of Northern Ireland (ARINI) – in Belfast saw numbers of cases of chronic copper poisoning in sheep peak during the summer of 2015.

While copper is an essential part of enzymes governing many biological functions, sheep are particularly susceptible to the toxic effects of excess copper.

Toxicity is most frequently observed in the Charollais, Texel and Suffolk breeds, and less frequently observed in the mountain breeds. Clinical disease follows a period of excess intake and occurs when the liver’s capacity to store excess copper is exceeded and there is a sudden release of copper by the liver.

This typically occurs after weeks or months of accumulation of copper and often coincides with a period of stress on the animal. The sudden release of copper by the liver causes haemolysis and irreversible damage to the kidney and the brain. Copper poisoning is slow to develop but sudden in onset.

The eyes and skin become jaundiced and post mortem examination reveals an orange liver, black kidneys and red/brown urine. Biochemistry results show a toxic level of copper in the liver and the kidney. Serum copper levels do not provide a reliable warning of imminent toxicity. While blood tests for liver enzymes can assess how much damage has occurred to the liver, these tests are not specific for copper toxicity and liver damage can be due to other conditions such as the presence of parasites.

Feeding concentrates containing high levels of copper, excessive administration of copper containing mineral supplements or boluses, and grazing pastures which have been dressed in pig slurry are typical scenarios in which cases of copper toxicity in sheep may develop. However, even a diet with an acceptable copper concentration can also cause subclinical toxicity if fed for long enough to vulnerable breeds.

This is because copper is a cumulative poison with the combination of daily exposure and prolonged feeding playing a part. Every opportunity to reduce the concentrate intake between lactations should be taken. Particular care should also be taken with rams as they are usually fed concentrates more regularly and for more prolonged periods.

Treatment options exist but they are only effective in the early stages of the clinical disease and are not always effective.