Forage level and particle size effects on orchardgrass digestion by steers: II. Ruminal digestion kinetics of cell...

Four steers (502 +/- 49 kg) with ruminal cannulas were used in a 4 x 4 Latin square experimental design with a 2 x 2 factorial arrangement of treatments to determine the effects of the dietary forage:concentrate ratio (96:4 and 60:40) and forage particle size (long hay and coarsely ground hay) on in situ ruminal digestion kinetics of orchardgrass hay DM and cell wall neutral monosaccharides, uronic acids, acetyl groups, and hydroxycinnamic acids. Dacron in situ bags containing orchardgrass hay were fermented for 0, 4, 8, 12, 18, 24, 48, and 96 h. Digestion profiles of DM and cell wall monomers in undigested residues recovered from the rumen were analyzed using a first-order, exponential equation to estimate the indigestible fraction (fi), the insoluble, potentially digestible fraction (fd), and the fractional rate constant (kd) of digestion of fd. Initial results indicated that fi was not consistently influenced by diet fed to the steers; thus, in situ digestion profiles were analyzed to estimate single fi and fd values common to all steers and diets and different estimates of kd for each steer x diet combination (16 total). Estimates of fi (percentage of original) for cell wall components were ranked in the following order: galactose (12.6), ferulic acid (13.9), arabinose (14.5), total uronic acids (15.4), glucose (19.8), xylose (28.4), p-coumaric acid (34.6), and acetyl groups (35.8).(ABSTRACT TRUNCATED AT 250 WORDS)