Methane (CH₄) is a potent greenhouse gas. Methane enteric production by ruminant livestock is one of the major sources of greenhouse gas emissions. Enteric produced CH₄ also represents the energy not used by the host animal and accounts 2–12% of gross dietary energy through eructation.

Gaining more insight into the methanogenesis in ruminants would be helpful for developing strategies to mitigate enteric CH₄ emissions and increasing dietary energy use efficiency of animals. In the rumen of ruminants, CH₄ produced from formate is one of the important methanogensis pathways.

In order to explore the mechanistic insight in the formation of CH₄ and quantitatively evaluate the ruminal methane formation from formate, researchers from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the carbon flow from formate to CH₄ and CO₂ using stable isotopic formate with ¹³C in a batch culture system, where the inocula of ruminal fluid was collected from ruminally-fistulated goats to represent the ruminal environment.

The researchers found that the formate can be rapidly dissimilated into CH₄ and CO₂ by rumen microorganisms. "Approximately half (48.9%) of the stable isotopic carbon was converted from carbon-formate into carbon-CH₄ and carbon-CO₂ within the first 6 hours, the conversion rate increased up to 80% after 24 hours, and the maximum total conversion rate was approximately 95%," said HE Zhixiong, a researcher at ISA.

"Usually in the rumen of ruminants, formate is easily neglected for its low concentration. Our results indicate that the very small amount of formate detected in ruminal fluid may be likely due to a rapid dissimilation rather than a low production. The microbes can also ferment carbohydrates to make formic acid but which could be rapidly dissimilated into CH₄ and CO₂," HE added.

This research was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, and Pioneer Hundred Talents Program of the Chinese Academy of Sciences.

The study entitled "Quantitative evaluation of ruminal methane and carbon dioxide formation from formate through C-13 stable isotope analysis in a batch culture system" was published in animal.

Contact: HE Zhixiong

E-mail: zxhe@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences