The treatments consisted of different digestibility evaluation methodologies, consisting of a direct method with total feces collection (TC) and an indirect method using internal markers cellulose (iCEL) and indigestible lignin (iLIG), obtained through in situ (IS) techniques in cattle and in vivo (IV) techniques in equines using MNB, totaling five treatments.
The digestion residues were submitted to extraction by acid detergent, resulting in lignocellulose; the remaining fraction underwent cellulose solubilization by sulfuric acid at 72% (VAN SOEST et al., 1991), thereby obtaining markers iCEL and iLIG.
Despite the differences between the methodologies in assessing indigestible markers, the observed concentrations of iCEL and iLIG in the current study were adequate in enabling similar recovery rates to the TC group (p > 0.05).
In an attempt to overcome the limitation regarding the disappearance of LIG during gastrointestinal transit, the present study proposed prior incubation in a microbial environment, and its chemical assessment, thereby obtaining iLIG. Thus, the levels of 3.77 and 4.79% for iLIG in vivo and in situ, respectively, were satisfactory, as confirmed by their high feces recovery rates.
Estimates of feces production, presented in Table 3, were adequately predicted by iCEL and iLIG regardless of technique used, resulting in an average of 2.79 kg of feces in DM.
The DCs of DM, OM, CP, NDF and starch determined by TC were similar (p > 0.05) to those estimated by iCEL and iLIG in both techniques.
The efficiency of iLIG in estimating nutrient DCs in the present trial indicates that only the indigestible fraction of lignin should be used as a marker in digestibility trials.