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Journal of Dairy Science Vol. 84 No. 6 1438-1444
© 2001 by American Dairy Science Association ®
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Assessment of Rumen Processes by Selected-Ion-Flow-Tube Mass Spectrometric Analysis of Rumen Gases

R. J. Dewhurst 1, R. T. Evans 2, T.T. Mottram 3, P. Spanecaronl 4, and D. Smith 5

1 Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK
2 Institute of Grassland and Environmental Research, Trawsgoed Research Farm, Trawsgoed, Ceredigion SY23 4LL, UK
3 Silsoe Research Institute, Wrest Park, Silsoe, Bedfordshire MK45 4HS, UK
4 J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 182 23 Prague 8, Czech Republic and Centre for Science and Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke-on-Trent ST4 7QB, UK
5 Centre for Science and Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke-on-Trent ST4 7QB, UK

This work investigated the potential to use measurement of the concentration of certain gases in the rumen headspace to gain information about rumen processes and as a potential diagnostic tool. We used new equipment (selected-ion-flow-tube mass spectrometer) that allows rapid and precise analysis of many of the gases present in a sample. Samples of rumen headspace gas and corresponding samples of rumen liquor were taken from three lactating cows, prepared with rumen fistulae, at intervals after receiving their morning feed allocation (grass silage and concentrates). Hydrogen sulfide, methyl sulfide, and dimethyl sulfide, were the predominant gases that were measured in the rumen headspace by this technique. The concentrations of these sulfur compounds declined over the interval after feeding, mirroring ammonia concentrations measured in rumen liquor, reflecting their common dependence on the fermentation of sulfur amino acids. Ammonia concentrations in rumen headspace gas varied in the opposite direction to the concentration of ammonia in rumen liquor and likely depend more on the pH of rumen liquor. Consideration of the pKa of ammonia suggests that ammonia concentrations in rumen gas will be very low below pH 6, representing a useful diagnostic for subacute ruminal acidosis. Low concentrations of volatile fatty acids were detected in rumen gas. The molar proportions of volatile fatty acids were similar in gas and liquor samples, with rumen gas containing slightly less acetic acid and disproportionately more valeric and caproic acids.

Key Words: dairy cow • rumen • gas analysis • mass spectrometry

Submitted on September 18, 2000
Accepted on February 8, 2001




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