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

Abstract

The effects of various treatments on the gas production (GP) profile of high temperature dried grass (HTDG) incubated in vitro with buffered rumen fluid were recorded. The treatments investigated were increases in the concentration of rumen fluid (from 5% to 30%, v/v), mixing medium with the substrate from 0 h to 48 h before inoculation, and blending the rumen fluid prior to inoculation. Increasing rumen fluid concentration decreased final culture 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 production ( T 1/2, p < 0.05), increased the fractional degradation rate ( μ) at 1 h ( p < 0.001) but did not affect μ at T 1/2 and 48 h. There were two phases 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 reach the second phase ( p < 0.001). Mixing the substrate with medium prior to inoculation decreased T 1/2, increased A and μ at T 1/2 and 48 h ( p < 0.001) but had no effect on μ at 1 h. The rate of the initial phase of the reaction was not affected but the rate of the second phase was increased and took 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 < 0.001), increased μ at 1 h ( p < 0.001) but had no effect on μ 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 reaction if the substrate was mixed with the medium for 6 or 48 h, except that μ at 1 h was greater if the pre-incubation time was 48 h. Blending the rumen contents prior to inoculation did not affect the GP profile or reaction rate. The results indicate that the rate of gas production may be enhanced by increasing the rumen fluid concentration and mixing the medium with substrate prior to inoculation for up to 48 h. There is no benefit from blending the rumen contents prior to inoculation.