Determination of the concentration of metals in animal feeds

The concentrations of eight metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined by atomic absorption spectrophotometry for the following related materials: three products obtained by processing cattle manure—a cellulosic material resembling silage (CI), a water soluble protein-rich powder (CII), and a soil amendment product (CIII)—as well as dairy cattle feed rations containing CII and the resultant fresh feces; and the manure composites used to prepare the processed products. The concentrations of these metals generally increased in samples in the order feed, feces, CI, CII, and CIII. The metal concentrations in CI were comparable to literature values for silage; the metals in CII were present at higher concentrations, but not sufficient to limit its use as a feed ingredient. The potential health effects of feeding cattle rations containing CI or CII are discussed in the context of these results.