Introduction
In recent years, livestock production systems, especially
those common in intensive swine farming has been
utilizing zinc oxide (ZnO) and copper sulfate (CuSO4)
as growth promoters (Salyer et al., 2004). When added
to feeds, these two compounds improve feed utilization
and the growth of farm animals (Hojberg et al., 2005;
Li et al., 2006). At the same time, there has been a rise
in environmental problems and public conflicts associated
with intensive livestock production. Similarly, over the past
few decades, there has been an increase in environmental
pollution from the disposal of excess animal manure. As
a result, many new regulations and directions are being
implemented at the national and European Union (EU)