Effect of forage source on retention of digesta markers applied to corn gluten meal and brewers grains for heifers.

Effect of forage source on retention time of dietary protein supplements in the rumen was measured, and solid and liquid markers of digesta passage were compared. Two markers for liquid, two for each of the forages, and two for each of the supplemental proteins were compared for estimating retention time. Eight Holstein heifers were allocated to a single-reversal design with two periods of 29 d each. Heifers were fed either alfalfa hay or corn husks and leaves combined with one of two resistant protein sources: corn gluten meal or wet brewers grains. Average rumen liquid retention times, measured with Co-EDTA or Cr-EDTA, were similar (16.2 to 16.9 h). Liquid retention times differed when alfalfa or corn residue was fed (14.1 and 18.9 h, respectively). Rumen retention times were similar for Sm and Ce (24.9 to 26.3 h) and across markers for forage sources (25.1 to 26.1 h). Total tract mean retention time was higher for corn residue than for hay (57.8 vs. 48.8 h). Rumen retention times for La and Yb (27.1 and 26.0 h) applied to protein sources were similar and were not different when applied to corn gluten meal or brewers grains (26.3 and 26.8 h). Forage source did not have an effect on the retention time of protein supplements. Low daily DMI of 2.22 and 1.91% of BW for hay and corn residue diets explain the rather long retention times of the protein supplements. Both Co-EDTA and Cr-EDTA were effective as liquid phase markers.