aNDFom degradation behavior in non-forage feeds

Previous work conducted in our lab demonstrated that the extent of NDF degradation in nonforage fiber feeds is achieved by 120 h and results in undigested NDF (uNFD). Further, Raffrenato (2011) demonstrated that aNDFom degradation kinetic can be characterized with a dynamic model utilizing 4 data points (0, 30, 120 and 240 h). The objectives of this study were to characterize the degradation behavior of aNDFom, and to determine the time points required to model and calculate the degradation parameters, in nonforage fiber feeds. Samples of 12 feeds (citrus pulp, beet pulp, wheat middlings, soy hulls, corn germ, corn gluten feed, wheat distillers, corn ethanol distillers, flaked corn, rice hulls, soybean meal, and canola meal) were collected, each from 2 providers, and analyzed in duplicates and in 3 separate batches for NDF digestion kinetics using the in vitro technique. Fermentations were conducted for up to 3, 6, 9, 12, 15, 18, 21, 24, 30, 48, 72, 96, 120 h following the methods of Goering and Van Soest (1970). Residues were filtered on a glass microfiber filter (934-AH, Whatman). To study the digestion behavior of non-forage fiber NDF, the degradation curves were plotted on semi-log scale, and analyzed to determine the inflection point of the aNDFom residues. Overall, the natural log-transformation, demonstrated that NDF digestion in nonforage fiber feeds can be described by one degradable pool (no inflection points). To determine the time points, 7 combinations of 4 data points corresponding to: 0 h, 2 intermediate time points, and uNDF were used as inputs. The corresponding slope and intercept of each regression (observed on predicted) were then compared. The accuracy of the model did not allow for detecting statistically significant differences in slope and intercept among time point combinations, however 0, 12, 72, and 120 h were the time points that provided model predictions with an average slope and intercept closest to unity and zero respectively (intercept = 0.04, slope = 0.95). Thus, for routine determination of non-forage fiber digestibility and the estimation of rates of degradation for use in nutrition models, these time points provided adequate information among the feeds analyzed