The effect of in vitro fermentation on specific gravity and sedimentation measurements of forage particles

Dry matter degradability(DMD), gas production (GP), functional specific gra vity (FSG), volume of gas associated (GA), water-holding capacity (WHC), an d sedimentation measurements of orchardgrass (OG) and alfalfa (AA) hays (gr ound through a 8-mm screen) were studied before and after in vitro incubati on with ruminal fluid for 2, 4, 8, 24, 48, and 72 h. The DMD was higher for AA than for OG (P < .001), but GP did not differ. The FSG of unfermented O G and AA was .59 and .73, respectively (P < .01). During fermentation, the FSG of OG increased more than did that of AA. (from .93 to 1.39 for OG and from .97 to 1.27 for AA after 2 and 72 h, respectively), and GA decreased m ore rapidly (from .94 to -.04 mL/g DM and from .74 to .15 mL/g DM, respecti vely). The DMD was positively correlated with FSG (r = .83; P < .001) and, therefore, negatively with GA (r = -.72; P < .01). The WHC increased simila rly in the two forages with fermentation time. Unfermented and fermented sa mples were incubated in sedimentation columns filled with distilled water f or 19, 37, 75, 150, and 300 s. After 300 s of sedimentation time, the unfer mented AA and OG samples tended to float (91.1 and 72.7% of DM, respectivel y). In contrast, fermented samples tended to sediment (90.7 and 90.9% of DM , respectively). There were only small effects of forage species and fermen tation time on sedimentation tendency. Correlations between sedimentation m easurements and DMD and FSG were not significant, with the only exception o f DM recovered in the lower section of sedimentation columns after 75 s, wh ich was particularly correlated with DMD (P < .01) and FSG (P < .05). The r esults suggest that degradation rate of fibrous particles is related to cha nges in FSG and GA and, therefore, could influence ruminal transit. However , FSG was unable to predict accurately the sedimentation behavior of sample s.