On request from the Norwegian Food Safety Authority, the Norwegian Scientific Committee for Food Safety, Panel for Animal Feed has assessed the fate of Zn and Cu from feed and other sources, via pig and poultry intake to manure, and further to soil, and the long term effects in the food chain and environment.
Zinc (Zn) and copper (Cu) are essential trace elements in plant, animal and human nutrition, and animal manure is a source of great value for fertilisation of agricultural soil.
The requirement of Zn in pigs may vary within 25 – 80 mg/kg diet dependent on the type of production and the feed composition. The requirement of Zn in poultry may correspondingly vary within 30 – 60 mg/kg diet.
Lower levels are sufficient in feed without whole-grain products and plant proteins containing phytic acid, a storage form of phosphorus which reduces the bioavailability of Zn. The requirement of Cu in pigs is 3.5 – 5 mg/kg and in poultry 4 – 8 mg Cu/kg diet, mainly dependent on type of production.
The data on Zn and Cu in complete compound feed in Norway indicate exposure of Zn and Cu to pigs and poultry at least two times higher than the requirement but most often several times above the required level.
In addition, piglets are commonly fed complementary feed with Zn and Cu, as well as Zn in medical remedies.
The estimated extra exposure via complementary feed is rather marginal but the medical use of Zn against diarrhoea and oedema disease in weaned piglets is considerable.
The use of Zn as medical remedy is at a level of approximately 15-20 times higher than the exposure via complete feed and 30-60 times above the normally required level.
The results of the present suggested overload of Zn and Cu in feed for pigs and poultry and reduced bioavailability of Zn and Cu as well as of other essential trace elements in the animals are high levels of these elements in the manure.
Zn and Cu exposure of bacteria in livestock and the environment may develop resistance to Zn and Cu and there are links to antibiotic resistance.
In the long run, elevated concentrations of Zn and Cu in manure may adversely influence organisms in the environment and the food chain and be of health concern for human consumers.
Reduction in animal intakes of Zn and Cu via feed, additives and medical remedies is possible to carry out respecting animal health and seems necessary respecting adverse effects in the environment and food chain.