ABSTRACT
A variety of heavy metals and rare earth elements, particularly those forming strong bonds with feed/digesta particles, have been successfully employed as particulate markers. An important prerequisite is that these elements are either not present or present in minimal concentration in soil and plants. Metal oxides (Cr and titanium) have been proposed as digestibility markers. Chromium sesquioxide (Cr2O3) is one of the most commonly used digestibility markers, but it is an unreliable passage marker because its physical properties and flow kinetics have little resemblance to the flow characteristics of any digesta fraction.[2] Chromium forms strong ligands with plant cell wall constituents, and Cr-mordanted fiber is used as a particulate flow marker.[7] Nonfiber substances are removed before binding in order to improve retention of Cr on the cell wall matrix. Concentration of Cr, however, dramatically increases the density and reduces digestibility of the labeled particles. It is recommended that the Cr concentration be reduced to 10 g/kg hay (or 23 g/kg feed pellets) in order to minimize the effect of the heavy metal on particle density.[4] Particle size of the Cr-mordanted fiber can also significantly affect the rate of passage.
