INFLUENCE OF MOISTURE-CONTENT OF FORAGE ON RUMINAL FUNCTIONAL SPECIFIC-GRAVITY AND PASSAGE OF DIGESTA

Four crossbred beef steers (392 kg BW) fitted with ruminal cannulas we re used in a 4 x 4 Latin square experiment with treatments arranged in a 2 x 2 factorial to evaluate effects of forage species (F) and recon stitution (R) on apparent digestibility, ruminal kinetics, and digesta functional specific gravity (FSG). Dietary treatments were alfalfa (M edicago sativa L.) and timothy (Phleum pratense L.) hays (90% DM) and the same hays reconstituted with water to 38% DM. Apparent DM digestib ility was unaffected by R or F. Proportion of ruminal digesta with a F SG of .9 to 1.1 or 1.1 to 1.2 decreased linearly (P < .05) after feedi ng, whereas the proportion with FSG > 1.2 increased Linearly(P < .01). Reconstitution decreased (P < .10) the proportion of ruminal digesta with FSG of 1.1 to 1.2 and increased (P < .10) the proportion with a F SG > 1.2 compared with the hay diets. Reconstitution decreased digesta passage rate for timothy forage; no influence on passage rate for alf alfa was detected (F x R, P < .10). Ruminal DM pool was increased by r econstitution (P < .10). Inert particles of l-mm length passed from th e rumen at a faster rate (P < .05) than 3-mm particles. Inert particle s with SG of 1.32 passed from the rumen at a faster rate (P < .05) in the reconstituted alfalfa than in the dry alfalfa diet but at atl a sl ower rate in the reconstituted timothy than in the dry timothy diet. T hese results suggest that factors other than SG of the digesta can hav e a profound effect on passage of forage particles from the rumen.