Rumen fluid is used as fresh inoculum for gas production fermentations to predict the nutritional value of feeds and rations for ruminants. However, collection of rumen fluid from animal donors is invasive, expensive, time consuming and results in fluids of variable quality. The general aim was to identify a procedure to manipulate rumen inoculum in order to facilitate its storage and transfer between laboratories. This strategy would also limit fluid collections from animals. Two experiments were completed based on gas production from graduated 100 mL glass syringe with five feeds as substrates. In experiment 1, the gas production and some fermentation parameters of fresh rumen fluids were compared with those preserved at 4 °C for 24, 48, 72 and 96 h. Refrigeration did not modify concentration of volatile fatty acids and pH, but ammonia in liquids refrigerated for 48–96 h was higher (P < 0.05) compared to fresh. In contrast, rumen fluid refrigeration for 24, 48 or 72 h did not depress gas production at 24 h, but it was lower at 96 h. In experiment 2, the rumen fluid was centrifugated at 13,000 x g and sedimented material (i.e., pellet) was refrigerated for 48 h at 4 °C. The asymptote of gas production kinetics from rumen fluid regenerated from the pellet was 8 % lower (P < 0.05) than that from fresh. However for 24 h gas production, the correlation between fresh liquid and pellet inoculum, calculated for five ingredients, was high (R2 = 0.94). Results support the use of rumen fluid preserved by refrigeration for up to 72 h, and rumen fluid reconstituted from refrigerated pellet, as an alternative to fresh. This would reduce the need for laboratories to maintain animal donors and/or frequently collect rumen fluid.
