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Simplified in situ method for estimating ruminal dry matter and protein degradability of concentrates¹

V. Olaisen^*, T. Mejdell, H. Volden^,1 and N. Nesse^*,2

^* Department of Chemical Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim; and SINTEF Applied Chemistry, Chemical Engineering, NO-7465 Trondheim, Norway; and and Department of Animal Science, Agricultural University of Norway, NO-1432 As

² Correspondence:
P.O. Box 5025 (phone: +47-64-94-80; fax: +47-64-94-79-60, E-mail:
harald.volden{at}ihf.nlh.no).

In this study, dry matter and crude protein in situ degradation data from different concentrate feeds were used to test the accuracy of effective degradability (ED) measures when using reduced ruminal incubation times compared with models based on seven or eight incubation times. The ED was estimated both with and without correction for nylon bag particle loss. The crude protein ED corrected for particle loss of the calibration data set was widely distributed in a range from 16 to 90% with an overall mean value of 60.4%, and the dry matter ED was distributed in the range from 22.7 to 80.7%, with a mean value of 56.9%. The simplified method was developed based on bilinear regression models where all combinations of one to three disappearance values were tested to find the optimal time point combinations to estimate ED. Bilinear regression models based on two and three ruminal incubation times gave similar estimates to a standard in situ method over a wide range of passage rates both for the data set used to parameterize the models and the independent data set used to evaluate the models. Using two incubation times, the bilinear model based on 4 and 24 h gave the most accurate estimates, and the models based on 2, 8, and 24 h for uncorrected data and 4, 8, and 24 h for corrected data were most accurate of the three time points bilinear models. The number of nylon bags used by these models was reduced by 58 to 78% compared with the standard in situ method, and the total incubation time needed was substantially reduced.

Key Words: Cattle • Degradation • Dry Matter • Mathematical Model • Protein • Rumen