In vitro screening of methane production from grass and maize silage based dairy diets

摘要

In two in vitro experiments the methane and volatile fatty acid production of simulated dairy diets was screened. Methane production was measured after 21 hours of fermentation of 450 mg substrate, in a phosphate buffer at 39°C under anaerobic conditions. Methane production was measured in headspace gas, by gas chromatography. Volatile fatty acid production was measured by gas liquid chromatography. Substrates were composed of different feedstuff, simulating various dairy diets. In experiment 1 three types of grass silage and three types of concentrates were tested in a 3x3 factorial design. The three grass silages increased in digestibility of the organic matter, whereas the concentrates increased in fermentation rate of the organic matter, the latter caused by an increasing starch content. In experiment 2 the effect of the increasing digestibility of the grass silage was tested again, in combination with three types of maize silage, differing in dry matter content. In experiment 1 methane production tended to increase with increasing digestibility of the grass silage, which was contrary to expectations. However, the increase in digestibility was mainly caused by an increasing sugar content, which seemed to cause a more butyric acid directed fermentation pattern, resulting in more methane. The effect of concentrate on methane fermentation was unclear, with both the low and the high fermentable concentrate leading to a low amount of methane production. In experiment 2 the grass silages with an increasing digestibility tended (not significant) to induce a lower methane production, as initially expected. There was no effect of dry matter content of the maize silage on methane production. When the results of experiment 1 and 2 were combined, the presence of maize silage in the diet had a highly significant effect on the fermentation parameters. Methane, acetic and butyric acid production were reduced, whereas propi-onic acid production was increased. For methane production there was a weak interaction between the presence of maize silage and type of grass silage. The methane production seemed to be stimulated by increasing dietary sugars whereas higher amounts of dietary starch reduced rumen methane production. These results indicate that an increased use of maize silage in dairy diets could be a tool to reduce methane production.