Technical note: evaluation of acid detergent lignin, alkaline peroxide lignin, acid insoluble ash, and indigestible acid detergent fiber as internal markers for prediction of alfalfa, bromegrass, and prairie hay digestibility by beef steers.

Six steers (BW = 436 +/- 15 kg) were assigned randomly to alfalfa, bromegrass, or prairie hay diets in a replicated 3 x 3 Latin square design to evaluate the efficacy of different internal markers for estimating OM digestibility (OMD). Internal markers used to estimate OMD included ADL, alkaline peroxide lignin (APL), AIA, and indigestible ADF (IADF), which consisted of a 144-h in vitro incubation (IADFWOUT), indigestible ADF with acid/pepsin pretreatment of feed and orts samples (IADFFEED), or acid/pepsin pretreatment of feed, orts, and fecal samples (IADFALL). Marker-derived estimates of OMD were compared with OMD measured by total fecal collection (TFC). For the alfalfa diet, all marker estimates differed (P less than .05) from the TFC measurement; however, lignin-based procedures (ADL and APL) and IADF with acid/pepsin pretreatment (IADFFEED, IADFALL) were numerically closest to TFC values. Estimates of bromegrass and prairie hay OMD by ADL, APL, and AIA ratio were not different (P greater than .05) from TFC measurement, although AIA seemed to provide the most accurate estimate for prairie hay. All indigestible ADF procedures yielded estimates of forage OMD that differed (P less than .05) from TFC for all forages; acid/pepsin pretreatment of samples (IADFFEED and IADFALL) improved accuracy of the OMD estimates in all forages. Likewise, recovery of indigestible ADF was consistently least among the markers evaluated. These results indicate that APL ratio performed similarly to ADL ratio in estimating forage OMD, that AIA estimated grass OMD very accurately, and that estimation of OMD by indigestible ADF ratio was improved when the procedure was accompanied by an acid/pepsin pretreatment of samples.