Dear A. Selvaraj,

I found your question to be interesting.

Demeyer (Demeyer, D. I. (1991). Quantitative aspects of microbial metabolism in the rumen and hindgut. Rumen microbial metabolism and ruminant digestion, 217-237.) published an approximation that you might want to consider:

In the absence of other acceptors and donors and based on the molar proportions of the metabolites in question,  2H released = 2H accepted

2H released = 2 acetate + propionate + 4 butyrate = 4 methane + 2 propionate + 2butyrate = 2H accepted.

Of course you need to consider other processes such as biohydrogenation, but that could be an starting approach. Look at Demeyer for further elaboration.

Kind regards,

Dear Professor Rolando Barahona Rosales, Thank you for your reply and I workout with this calculation.

Kind regards

I don't know if this answer the question, but the Hydrogen production will be dependent on the balance between acetate/propionate/butyrate. 

Acetate production yields 2 H per mole of pyruvate fermented (in either both pathways):

pyruvate + H20 + ADP + pi = Acetate + ATP + CO2 + 2 H

Propionate production takes (uses !) 4 mole hydrogen (in both  pathways) per mole:

Pyruvate+ 4 H =  propionate + H2O

Butyrate is neutral, because it generates hydrogen when pyr is converted to acetate, but then thos hydrogen are used in butyrate production.

So, the total production of Hydrogen depends on the ruminal stoichiometry and those VFA ratio, mainly acetate and propionate. 

I think that  Quantitative aspects of rumen digestion and metabolism, edited by Disjktra, France and Forbes, can be a good guiding book.

I hope to have helped.

In ruminants, methanogenesis is characterized by a two stage process: (i) the enzymatic degradation of feed sources in the rumen with the release of a range of monomers (sugars, amino acids, glycerol and fatty acids) and (ii) the fermentation of those compounds rumen microbiota (bacteria, protozoa and fungi).  The primary fermentation products are short chain volatile fatty acids (acetate, propionate and butyrate), fermentation acids such as lactic acid, formic acid, a range of alcohols (for example ethanol), succinate and branched chain volatile fatty acids.  In addition, CH4, CO2, H2 and ammonia are also produced.

To maintain ruminal functionality, clearance of volatile fatty acids, H2 and CO2 must occur or there will be (i) a substantial reduction in yield of microbial biomass reflecting change in pH and (ii) an alteration in the rumen DM pool turnover (REF).  Volatile fatty acids are transported across the rumen and omasal walls and utilized by the animal whereas CO2 is released to the head space of the rumen and lost via eructation or transported via circulation to the lungs and respired.  Clearance of metabolic H2 is via formation of VFA or converted to CH4 as part of the mechanism to clear the product from the site of fermentation. This process is facilitated by methanogenic Archaea.  If this process is not maintained, H2 accumulates and re-oxidation of NADH, NADPH and FADH to NAD+, NADP+ and FAD+ is reduced leading to a reduction in dehydrogenase activity involved in the oxidation of reduced cofactors, microbial yield and production of fermentation products (volatile fatty acids and fermentation acids: REF).  McAllister and Newbold (2008) suggested that if H2 was removed efficiently from the rumen environment, the rate of fermentation may increase reflecting the removal the potent inhibitor (H2) of microbial degradation of ingested feeds. It is not a simple proposition to calculate hydrogen yield from VFA as there are three metabolic pathways to consider: 

Major metabolic pathways

 Hydrogenotrophic

CO2 + 4H2 > CH4 + 2H2O

Methylotrophic

CH3OH + H2 > CH4 + H2O

4CH3OH > 3CH4 + CO2 + 2H2O

CH3NH2 + H2 > CH4 + NH3

Aceticlastic

Minor in rumen

In general, the production of VFAs ratios in the rumen, depends on the hydrogen production.  The production  of propynic acid in the rumen is a hydrogen utilizer and production of acetic and butyric acids in the rumen is hydrogen releaser. So, there is  no short cut formula to estimate hydrogen in the rumen. but you can postulate some equations depends on the above answer given by     Dr. Julian  and Mariono. Further, you can go through  some review articles of Afshar and Naser 2011 and another article by Lee and Beauchemin Published in Canadian Journal of Animal sciences, 3 Sept. 2014. I think you can get some answer.