Role and environmental impacts of copper and zinc in pig farming: from feed to agricultural soils

Zinc and copper are heavy metals that may have short-or long-term environmental risk for agricultural soils on which pig manure is spread. Zinc and copper are essential for pigs and farm performance, and they are added as supplements to the feed. Because of their low retention rate by animals, however, most of the amounts ingested are excreted in manure. Moreover, they are limited natural mineral resources. It is thus essential to characterize their flows better through the continuum of feed - manure - treatment - soils to manage their use better. A literature review of these flows indicates that adapting pig feed is the main mechanism available to decrease the release of zinc and copper into the environment. European Union regulations set maximum dietary concentrations of zinc and copper (e.g. 120 and 25 mg.kg(-1) DM for fattening pigs, respectively). Treating farm waste is another way to derive added value from these wastes and better control the transfer of zinc and copper to soils, by concentrating these elements in products that can be exported from pig farms to regions that need them. Thus, improved knowledge of their distribution through the production chain is necessary to manage their fate and evaluate their environmental risks better. More research is thus needed to refine feeding strategies that include zinc and copper, while maintaining animal performance and health and considering strategies of manure management and treatment, as part of the circular bioeconomy.