ATTD of CuSO4 in corn–SBM diets compared with
Cu(HMTBa)2 is that the phytic acid in the corn–SBM
diet may have formed complexes with CuSO4, which
rendered this Cu unavailable for absorption (Leeson and
Summers, 2001). The ATTD of Cu is increased by phytase
supplementation, which further indicates the negative
effect of phytic acid on the digestibility of Cu (Kies
et al., 2005, 2006). However, using Cu(HMTBa)2 instead
of CuSO4 may reduce the formation of phytate mineral
complexes and, therefore, decrease fecal Cu excretion
and increase Cu absorption and digestibility (Jolliff and
Mahan, 2012). The present results support this hypothesis