Methane abatement by optimizing fermentation
The effect of dissolved carbon dioxide (dCO2) on bacterial function has been not fully understood. I review the work of Russell (Lana et al., 1998, Russell, 1998) and suggests that dCO2 may be a more important determinant of bacterial function than pH.
Because the following lemmas:
When the pH is low, ruminal dCO2 is at the highest (Bjerrum plot).
During CO2 holdup, even if dCO2 is high, high HCO3- can lead to high pH (Herdenson-Hasselbalch, 1908).
Therefore:
There is a close and positive relationship between low A/P ratio (acetate to propionate ratio) and ruminal pH, meaning there is a close relationship between high dCO2 and propionate.
Diets that promote CO2 holdup will have a low A/P ratio independent of ruminal pH, as high dCO2 are independent of the pH value under CO2 holdup.
A positive and close relationship between low A/P ratio and CH4 (methane) confirms that H2 is used preferably for propionate in environments rich in ruminal dCO2.
Thus, competition of propionate-producing bacteria with methanogens for H2 is enhanced in high dCO2 environments.
Better growth of bacteria which produce propionate intermediaries: Lactate and Succinate.
Methanogens are outnumbered by H2 is utilised for high end energy products
These figures taken from Russell (1998) described the effect of pH on A/P ratio and methane. There was a close relationship between the A/P ratio and CH4 emissions, confirming the competition for H2 between propionate producing bacteria and methanogens. Methane emissions are less than 30% related to pH variations. Hay diets that normally do not accumulate dCO2 (Lemma 1), optimal dCO2 conditions for propionate production can be found only under low pH (Bjerrum plot). Whereas feeding Corn based diets provide always more available dCO2 promoting propionate production (Lemma 2). Consequently, methane emissions are lineraly related to the A/P ratio and are 100% related to ruminal dCO2 concentrations.
For instance, R. bovis produces LPS under starch-based diets and high dCO2 concentrations, LPS in turn increases ruminal viscosity which can lead to the disruption of CO2 effervescence and CO2 holdup and bloat (Wright, 1960, Cheng and Hironaka, 1973, Cheng et al., 1976). And, succinate and lactate bacteria, precursor of ruminal propionate, require dCO2 rich environments to growth efficiently (Wright, 1960, Samuelov et al., 1991).
The differences in milk yield capacity between pasture-fed and concentrate-fed cattle may be attributed to the formation of environments rich in ruminal dCO2, both diets provide similar nutritional value (Varga and Kolver, 1997, Kolver et al., 1998). As discussed, those conditions are only met in pasture and hay diets at low pH, resulting in intermittent periods with low A/P ratio (Carruthers et al. 1997; Laporte and Gibbs, 2009). Whereas high dCO2 environments found in diets that promote CO2 holdup, such as concentrate, and/or corn-based diets, lead to lower A/P ratio and low methane emissions through the day.
The relationship between ruminal pH and SCFAs concentrations in pastoral systems in New Zealand (Laporte-Uribe and Gibbs, 2009).
RumenAI’s wireless indwelling system based on the attenuated total reflectance infrared (ATR-IR) monitors ruminal dissolved carbon dioxide (dCO2) concentrations in real-time, providing valuable insights into rumen fermentation and aid in the development and deployment of effective methane abatement strategies.
Ruminal dCO2 is a crucial factor influencing rumen fermentation and methane production. The proposed ATR-IR system can monitor these molecules simultaneously, providing a more comprehensive understanding of rumen dynamics.
The importance of synchronizing dCO2 and dissolved hydrogen (dH2) availability for methane mitigation is that CH4 inhibitors may not be consistently effective due to the asynchrony between these two molecules and optimizing ruminal dCO2 concentrations through improved feeding strategies, supplements, or additives could enhance H2 sink into high-value by-products, optimize rumen fermentation, and increase feed conversion efficiency (FCE). making dCO2 monitoring a promising tool to reduce methane and enhance productivity.
Continuous monitoring of the ruminal environment with the proposed ATR-IR system would allow for real-time evaluation of the effectiveness of any developed lab strategy, warranting its results in commercial conditions and accelerating adoption by farmers.
Overall, RumenAI optimised strategies promise to improve our understanding of rumen fermentation and facilitating the development and deployment of effective methane abatement strategies.
