Evaluation of internal markers isolated by alkaline hydrogen peroxide incubation and acid detergent lignin extraction

Samples from two experiments were used to evaluate the potential of ADL and alkaline peroxide lignin (APL; isolated by sequential, alkaline hydrogen peroxide [AHP] incubation and ADL extraction) for predicting digestibility of warm-season grass diets. Experiment 1 evaluated the influence of level of sorghum grain supplementation on utilization of immature bluestem-range grasses, and Exp. 2 evaluated the influence of supplemental protein x energy level interaction on the utilization of dormant bluestem-range grasses. Internal markers isolated in feed, orts and feces were 1) ADL and 2) APL with AHP incubation either before (APL-PRE) or after (APL-POST) the acid detergent extraction step in the ADL procedure. Organic matter digestibility (OMD) was calculated from the ratio of marker consumed to marker excreted for each internal marker and was compared with OMD from total collection. For Exp. 1 a treatment x marker interaction was observed (P less than .01). The APL-PRE procedure yielded OMD coefficients similar (P greater than .10) to total collection values within most treatments, but OMD coefficients from APL-POST and ADL differed (P less than .05) from total collection within all treatments except at the highest level of supplementation. For Exp. 2, predicted OMD values from ALP-PRE were similar (P greater than .10) to total collection values, whereas OMD predictions from APL-POST and ADL were different (P less than .01) from total collection. In conclusion, APL appears promising as an internal marker for bluestem-range grasses if AHP incubation is incorporated before the acid detergent extraction in the ADL procedure.