Effect of preservation on fermentative activity of rumen fluid inoculum for in vitro gas production techniques

Use of preserved rumen fluid (RF) as microbial inoculum for in vitro gas production techniques (IVGPT) would be of practical importance when access to ruminally cannulated animals is limited. This experiment was designed to study effects of RF preservation on its subsequent fermentative activity. Four substrates being: alfalfa hay (AH), barley straw NDF (BS-NDF), cellulose and starch were incubated with rumen inoculum obtained from 12 rumen cannulated grazing sheep, of which six (G) received no supplement and the other 6 (G+S) received 500 g/day of a concentrate. Sub-samples of RF were processed without delay (i.e., control) or stored at approximately 0 °C in a chest with crushed ice for 3, 6 and 24 h (treatments 3, 6 and 24 h, respectively) or at −18 °C for 24 h in a freezer (treatment 24 F). An IVGPT was used to determine the rate and extent of gas production and DM disappearance. Average fermentation rate (AFR) and extent of degradation in the rumen (ED) were estimated. Incubations with inoculum derived from supplemented sheep (G+S) resulted in faster rates of gas production (with differences, as proportionate increases, of 0.77 for the barley straw NDF; P<0.01), lower lag times (e.g., 13.2 versus 4.0 h for the starch; P<0.05), and higher ED values (e.g., 229 versus 331 g/kg for the barley straw NDF or 173 versus 409 g/kg for the cellulose; P<0.05). Storing RF in ice for 3 or 6 h had no effect on any fermentation parameter. Treatment 24 h did not affect IVGPT parameters when starch and cellulose were fermented, but estimates of rates and ED were lower (P<0.05) with BS-NDF and AH. Fermentative activity of rumen inoculum was, in general, reduced by freezing (24 F). However, incubations of starch and cellulose were less affected by frozen inoculum than those of AH or BS-NDF. Preservation of RF for up to 6 h in crushed ice may be a practical alternative, when necessary, to use fresh RF as microbial inoculum.