AbstractNine forages of known nutritive value, as determined in conventional digestibility trials with cattle, were used as controls to further evaluate the artificial rumen or in vitro cellulose fermentation technique at 12 and 24 hours with the following results. The correlation of the relative intake (R.I.) and of the nutritive value index (N.V.I.) with 12-hour in vitro cellulose digestion was by no means the best. Low correlation coefficients (r) of 0.48 and 0.41, respectively, were obtained. Further research is needed to improve the efficiency and precision of the 12-hour fermentation. The 24-hour in vitro cellulose digestion in the artificial rumen gave the best estimates of the apparent digestibility of forages. Regression equations to predict biological T.D.N. (Y) and digestible energy (K cal./gm.) (F) from 24-hour in vitro cellulose digestion (X) were calculated: Y = 12.2 + 1.19X and Y = 0.75 + 0.05-X, and highly significant correlations of 0.98 and 0.90 were obtained. By means of these equations, the biological T.D.N, and digestible energy were calculated for all samples, and the results were tested statistically by means of the analysis of variance. N.V.I, correlated to 24-hour in vitro cellulose digestion and to 12-hour X 24-hour in vitro cellulose digestion gave coefficients of 0.70 and 0.71, respectively. In addition to the control samples, different forages, bromegrass, orchardgrass, and timothy from 13 different plots harvested on 4 first-cutting dates at 3 different locations in northern, central, and southern New Jersey, and fertilized with a complete fertilizer containing 50 pounds of nitrogen per acre, 1 plot receiving no nitrogen and 1 plot 100 pounds, were used in this study. They were evaluated by means of the artificial-rumen or in vitro cellulose-fermentation technique as a biological means of estimating their nutritive value. Advancing harvest dates (May 5 to June 6) were found to decrease the biological T.D.N, of orchardgrass, timothy, and bromegrass by 0.80 T.D.N, percentage units per day. It can be concluded that the 24-hour in vitro cellulose digestion can be used as a means of estimating the digestibility of forages or to predict T.D.N., or digestible energy, but the use of this 12-hour in vitro cellulose-digestion technique to predict intake or N.V.I, for cattle requires further refinement and precision.
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