Influence of inoculum source in a gas production method

Gas production techniques are used in many laboratories to study fermentation kinetics of ruminant feeds, and the major source of variation is often the inoculum. Fifteen substrates (two legume hays, two tropical grass hays, one fresh tropical grass, five temperate grasses, soybean meal, maize grain, maize silage, wheat straw, sugarcane bagasse) were used to measure fermentation gas release with a semi automated system, and a sigmoidal model was fitted to gas production data from rumen fluid collected from eight fistulated sheep and two cows. Comparisons were made between cattle and sheep inocula and between inocula prepared using different proportions (v/v) of rumen liquid and solid phases (1:0, 0.75:0.25, 0.67:0.33 and 0.5:0.5). There were no differences between estimates of asymptotic gas production, and organic matter digestibility, with the different species inocula, but rates of fermentation were higher with rumen fluid inocula from cattle versus sheep. Rumen contents with no solid phase produced more gas, whereas a 1:1 ratio of liquid:solid increased digestibility. However, the rate of gas production was not affected by the proportion of solid phase in the rumen inoculum.