Dietary means to better control the environmental impact of copper and zinc by pigs from weaning to slaughter

Because they are used as growth promoters or because large safety margins are applied, Cu and Zn are often oversupplied in pig diets. Consequently, manure is highly concentrated in these elements, which may concentrate in top soil and cause toxicity to plants and microorganisms. The reduction of Cu and Zn dietary supplies is one of the means to limit this environmental risk. The annual accumulation Cu and Zn in top soils could be reduced by 35% if Cu and Zn concentrations were reduced from 100 to 20 ppm and from 250 to 100 ppm, respectively, in fattening pig diets. However, to safely reduce Cu and Zn supplies, the dietary factors and mechanisms that significantly affect Cu and Zn availability should be better understood and ranked. In addition, ways to improve the availability of Cu and Zn, by the use of organic supplements and/or phytase, should be considered and their actual effectiveness in controlling pollution assessed. Particularly, if microbial phytase seems promising in reducing the Zn supply in pig feeding, the actual decrease in dietary Zn it allows remains to be assessed. (C) 2003 Elsevier B.V. All rights reserved.