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The objective of this study was to assess the variability among animals regarding the critical time to estimate the undegradable fraction of fiber (ct) using an in situ incubation procedure. Five rumenfistulated Nellore steers were used to estimate the degradation profile of fiber. Animals were fed a standard diet with an 80:20 forage:concentrate ratio. Sugarcane, signal grass hay, corn silage and fresh elephant grass samples were assessed. Samples were put in F57 Ankom® bags and were incubated in the rumens of the animals for 0, 6, 12, 18, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240 and 312 hours. The degradation profiles were interpreted using a mixed non-linear model in which a random effect was associated with the degradation rate. For sugarcane, signal grass hay and corn silage, there were no significant variations among animals regarding the fractional degradation rate of neutral and acid detergent fiber; consequently, the ct required to estimate the undegradable fiber fraction did not vary among animals for those forages. However, a significant variability among animals was found for the fresh elephant grass. The results seem to suggest that the variability among animals regarding the degradation rate of fibrous components can be significant.

It were performed two experiments to evaluate the utilization of industrial enzymes in the evaluation of NDF contents in high-starch materials. In the first experiment, it was verified the accuracy of estimates of neutral detergent fiber (NDF) obtained with the utilization of three industrial enzymes (Termamyl 2X, Liquozyme Supra 2.2.X, and Amylase AG 300L) at different volumes (50, 100, 250 or 500 mL/ sample). Samples were simulated to contain starch at 0, 100, 300, 500 and 1000 g/kg using purified cellulose and starch (n = 240). In the second experiment, samples of corn grain and sorghum grain were evaluated considering the same enzyme types and volumes used in the first experiment adding aliquots without using enzyme (n = 104). There was no significant bias of NDF recovery for simulated samples containing starch up to 300 g/kg. Considering those samples, none difference among enzymes was observed. It was observed a more intense decrease in NDF content according to each enzyme unit added on corn when compared to sorghum. Considering NDF evaluation in samples with mass of 0.7 to 1.0 g, it can be recommended the utilization of 250 mL the ?-amylases Termamyl and 2X Liquozyme 2.2X with activities of 240 and 300 KNU/g, respectively.