Influence of Dietary Protein and Energy on Disappearance of Dry Matter from Different Forage Types from Dacron Bags Suspended in the Rumen

In two experiments, crude protein was varied in corn silage diets (8.1, 11.3 and 13.3%) by urea addition and energy concentration was varied in alfalfa haylage diets by corn addition (0,30 and 60% of the dry matter) to determine dietary effects on dry matter disappearance (DMD) of three forage types (corn silage, alfalfa hay and grass hay) from Dacron bags suspended in the rumen of fistulated Holstein steers. Neither protein level nor energy concentration significantly affected DMD of any of the forages within bags removed after 24, 48 and 72 h of suspension, although the interaction for sampling time by forage type was significant with corn silage lower than alfalfa hay at 24 h (66 vs 72%), but higher at 48 and 72 h (82 vs 75%). Similarly, in vitro dry matter digestibility (IVDMD) was not affected by diet. Correlations between IVDMD and DMD were high (P<.05) for the 48 (.82) and 72 h (.59) rumen samplings but low for 24 h (—.16). As noted for DMD and IVDMD, in vivo dry matter digestibility was not affected by diet. Intakes were improved 13 and 38%, respectively, by urea addition to corn silage (P<.10) and corn to haylage (P<.05). The DMD of hay was increased (P<.05) by a 48-h pepsin digestion subsequent to removal from the rumen (72 vs 69%). The effect of pepsin was greater when forage type was alfalfa or grass hay than corn silage. Use of blanks in calculations also raised (P<.05) DMD (from 70 to 71%), except after pepsin digestion.