An increase in environmental concerns has been arisen with the growing of dairy farming in China, particularly greenhouse gases of methane and carbon dioxide. The ruminal methane production accounts for more than 80% of enteric methane emissions in ruminants and is the main source of methane emissions in ruminants. Meanwhile, the kinetic of in vitro gas production can indirectly reveal the progress for the ruminal degradation of nutrition, and has become a fast screen technique for the selection of feedstuffs and feed additives.

 

Scientists in Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) developed a new equation based on the assumption that the rate of gas production was positively correlated with the microbial mass and weight of incubated substrate. The equation was named by the logistic-exponential (LE) model (http://dx.doi.org/10.1016/j.anifeedsci.2010.09.016). Furthermore, they also upgraded the in vitro incubation system, which has equipment of automatic gas and liquid sampling and on-line data recording, and its corresponding data analysis software was also proposed.

The in vitro ruminal incubation system has several advantages, such as low costs, less labor and high repeatability, in comparison with the animal feeding experiment. However, its main disadvantage is for not considering the passage rate and the absorption of the nutrients in the rumen. Many studies showed that the kinetics of in vitro gas production helped to know the potential degradability of feed, but cannot indicate the real ruminal degradation of the feed in the ruminants, because the retention time in the rumen is normally less than 24 hours. To solve this problem, ISA’s recent study tried to divide the in vitro incubation into initial, middle and late stages, and proposed the equations to quantify the rate of these three stages, which provided the alternatives to extract more information underlying the kinetics of in vitro gas production (http://dx.doi.org/ 10.1017/S1751731112002443). It showed that feed with higher rate of degradation in the early stage have higher potential to be used for ruminant.

The volatile fatty acids production was always accompanied by the hydrogen production, which provide energy for the growth of methanogens and finally be oxidized into methane. As a result, hydrogen is an important intermediate among the volatile fatty acids, carbon dioxide and methane production. Hydrogen is not only the end products for hydrogen-producing microbes, but also the substrate for the hydrogen-using microbes, such as methanogens. The hydrogen gas accumulation is associated with complex balance of hydrogen production and consumption, which need to be quantified. ISA’s study proposed a new model to describe the kinetics of hydrogen gas accumulation, and the parameters of the model were closely related to the current knowledge of microbial hydrogen formation and consumption. This model provided an alternative to study the kinetics of hydrogen accumulation, and also expanded the implication of the LE model. Details of this research can be reached at http://dx.doi.org/10.1016/j.anifeedsci.2013.05.002.

This research was financially supported by the National Natural Science Foundation of China (Grant No. 31001023), “Strategic Priority Research Program - Climate Change: Carbon Budget and Relevant Issues” (Grant No. XDA05020700), and International Atomic Energy Agency (Grant No. 16315) for the joint financial support, and scholarship (No. 2010491254) from Chinese Scholarship Council.