- The objective of this study was to identify the varying effects of altering the rumen fluid: substrate ratio on the outcomes of in vitro rumen fermentation. In vitro fermentation is a useful tool for evaluating the energy value of feedstuffs and the effect of feed additives on Volatile Fatty Acid (VFA) production in the ruminant. In this study, rumen fluid was collected from 3 mature ruminally cannulated Holstein heifers, combined with a buffer, and incubated with increasing amounts of ground substrate. Increasing the ratio of substrate to inoculum caused an increase in total VFA production (mmol/L; P < 0.0001), as well as production (mmol/L) of propionic (P < 0.0001), valeric (P < 0.0001), acetic (P < 0.0001), and butyric acids (P < 0.0001). pH decreased as the inclusion rate increased (P < 0.0001), as did the ratio of acetic to propionic acid (P < 0.0001). The lag time (h) of fermentation was inversely related to the inclusion rate (P < 0.0001). Maximum gas production (mL/g DM) was only significantly decreased in the 8.0 g treatment (P < 0.0001). Between the ratios of 1.2, and 1.6 g dry substrate: 100 mL inoculum, none of the measured outcomes were statistically different (P > 0.05), and the environment of the fermenter units was comparable to that of the functioning rumen.
- Key Words: Rumen, Fermentation, Volatile Fatty Acid, Inclusion rate