Accurate and precise determinations of in vitro NDF digestibility (NDFD) are critical to proper evaluation of forage nutritive value, and essential for proper diet formulation for dairy cows. The objective of this research was to compare NDFD values determined with the Ankom Daisy Incubator II System (Ankom) using 2 sample sizes (0.25 or 0.50 g); a further goal was to compare these results with those obtained from a commercial laboratory using traditional methodology without any restraint of samples during digestion. All determinations of NDFD were conducted with NDF determined with heat-stable amylase and sodium sulfite, and corrected for residual ash (asNDFom). Triticale forages (n = 48) were incubated in triplicate for 12, 24, 30, 48, 144, or 240 h by Ankom methods. For the 30-h incubation, a regression of values obtained from the 0.25-g sample size on the larger, 0.50-g samples was explained by a linear model (Y = 1.206 x – 1.1; R² = 0.933), in which the slope differed from unity (P < 0.001), but the intercept did not differ from 0 (P = 0.661). After a 48-h incubation, a linear model (Y = 1.014 x + 7.1; R² = 0.964) indicated that the slope did not differ from unity (P = 0.631), but the intercept was greater than 0 (P < 0.001). A linear regression (Y = 1.040 x – 1.8; R² = 0.861) of NDFD using the 0.25-g sample size with Ankom methods on NDFD values obtained from the commercial laboratory indicated the slope and intercept did not differ (P ≥ 0.521), from unity and 0, respectively. A similar relationship was obtained from the 48-h incubation (Y = 1.021 x – 3.4; R² = 0.866). Relationships between Ankom and traditional methodologies were poorer for the 0.50-g sample size, particularly for the 30-h incubation, where the slope (0.824) was less than unity (P = 0.002). Generally, NDFD was greater by Ankom methods with the 0.25-g sample size, especially with short incubation times, and agreement with results obtained by traditional methods was improved relative to those obtained using a larger, 0.50-g sample sealed within fiber bags.