Effect of ensiling whole plant corn on voluntary intake, rumen fermentation, retention time and rate of digestion in steers.

The study was designed to determine whether products of fermentation in corn silage could limit its voluntary intake. Six rumen-cannulated Hereford steers were assigned randomly to diets of corn silage (CS) and dried corn forage reconstituted either with water (DC + W) or with extracts from corn silage (DC + CSE) according to a crossover design with three experimental periods. During each period, steers were fed ad libitum for 18 days and then restricted to 65 g DM/kg BW.75 for another 13 days. During the restricted feeding period, measures of rumen fermentation were made, and mean retention time (MRT) of rumen digesta was estimated after a single injection of the liquid and solid phase markers, 51Cr-EDTA and 103Ru-Phenanthroline complex (103Ru-P), respectively. Daily voluntary intake of DM (g/kg BW.75) for diet DC + W (80.2) was not diffferent (P greater than .05) from that for CS (89.7) but was significantly lower than that for DC + CSE (93.5). The corresponding estimates of MRT were 16.1, 14.1 and 17.4 hr (SEM +/- .5) for 51Cr-EDTA and 23.2, 23.9 and 24.3 hr (SEM +/- .7) for 103Ru-P. Measurements of osmolality, pH and VFA concentrations in rumen fluid were not related to daily DM intake. A study of rate of DM digestion, conducted by the rumen bag technique with samples of freeze-dried corn silage residue obtained after liquid extraction, yielded rate constants (hr-1) of .039 +/- .0030, .055 +/- .0028, and .0030 when steers were fed CS, DC + W and DC + CSE, respectively.