Effects of inoculum preparation method and concentration, method of inoculation and pre-soaking the substrate on the gas production profile of high temperature dried grass

The effects of various treatments on the gas production (GP) profile of hig h temperature dried grass (HTDG) incubated in vitro with buffered rumen flu id were recorded, The treatments investigated were increases in the concent ration of rumen fluid (from 5% to 30%, v/v), mixing medium with the substra te from 0 h to 48 h before inoculation, and blending the rumen fluid prior to inoculation. Increasing rumen fluid concentration decreased final cultur e pH (p<0.01), increased total gas production (A, p < 0.05) and gas yield ( p < 0.01), decreased lag time (p < 0.001) and time to half maximum gas prod uction (T-1/2, p < 0.05), increased the fractional degradation rate (mu) at 1 h (p < 0.001) but did not affect mu at T-1/2 and 48 h, There were two ph ases to the reaction, and increased concentration of rumen fluid increased the rate of the first phase (p < 0.001) and decreased the time taken to rea ch the second phase (p < 0.001), Mixing the substrate with medium prior to inoculation decreased T-1/2, increased A and mu at T-1/2 and 48 h (p < 0.00 1) but had no effect on mu at 1 h. The rate of the initial phase of the rea ction was not affected but the rate of the second phase was increased and t ook less time to attain (p < 0.001). Increasing the length of time that the substrate was mixed with the medium decreased lag time and T-1/2 (p < 0.00 1), increased y at 1 h (p < 0.001) but had no effect on mu at T-1/2 and 48 h. Initial rate of reaction was increased (p < 0.001) but the second phase was not affected, There was no difference in GP profile and rates of reacti on if the substrate was mixed with the medium for 6 or 48 h, except that mu at 1 h was greater if the preincubation time was 48 h. Blending the rumen contents prior to inoculation did not affect the GP profile or reaction rat e. The results indicate that the rate of gas production may be enhanced by increasing the rumen fluid concentration and mixing the medium with substra te prior to inoculation for up to 48 h. There is no benefit from blending t he rumen contents prior to inoculation. (C) 1999 Published by Elsevier Scie nce B.V. All rights reserved.