AbstractChromium (Cr) and acid-detergent lignin (L) were evaluated as index substances for determining digestibility of complete, low-fiber rations with growing steers. The rate of recovery of ration Cr was studied during depletion and repletion of the indicator. Total fecal collections were carried out for 7 days after a 1-day period of Cr intake. Recovered Cr for the 7-day period amounted to 85.5 ± 7.2 percent with a value of 82.3 ± 6.8 percent for the first 5 days, with a maximum amount of 30 percent on the second day. During the 21-day depletion following a 21-day repletion, fecal Cr decreased rapidly for the first 7 days and continued to decrease to 0.54 ± 0.02 percent at the end of the depletion. During 7-day and 10-week periods, L was recovered to the extent of 96.7 ± 0.5 and 96.6 ± 2.3 percent, respectively. Recovered Cr amounted to 94.4 ± 0.5 percent in long-term trials and to 90.5 ± 2.5 percent in short-term trials. In long-term trials, L was recovered to the extent of 94.1 ± 1.0 percent. No statistical differences (P < 0.05) were found among grab-sampling times or between grab samples and the total collection samples in rates of excretion of nutrients per unit of indicator. It was suggested that the differences in grab-sampling times were minimal when either Cr or L indicator techniques were used to determine digestibility. Recovery data tend to show that L is a valid marker and has the desirable characteristic of being a constituent of ruminant feedstuffs.
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