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United States Department of Agriculture

Agricultural Research Service

Title: Predicting the Partitioning of Fermentation Products by Combined in Vitro Gas Volume and True Substrate Degradability Measurements: Opportunities and Limitations

Author
item Blummel, Michael

Submitted to: European Association of Animal Production Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 1, 2000
Publication Date: August 15, 2000
Citation: BLUMMEL, M.R. PREDICTING THE PARTITIONING OF FERMENTATION PRODUCTS BY COMBINED IN VITRO GAS VOLUME AND TRUE SUBSTRATE DEGRADABILITY MEASUREMENTS: OPPORTUNITIES AND LIMITATIONS. EUROPEAN ASSOCIATION OF ANIMAL PRODUCTION PROCEEDINGS. p. 48-57. 2000.

Interpretive Summary: A theoretical model of the relationship between the rumen fermentation products short chain fatty acids (SCFA), microbial biomass and gases is presented and contrasted with in vitro and in vivo findings. A very close relationship was established between SCFA and gas production that allowed the calculation of a stoichiometrical factor (SF) to convert gas volumes into carbon, hydrogen and oxygen requirements for the production of a unit volume of gas. The range in SF values was 2.20 and 2.34 mg/ml for high acetate and high propionate fermentation, respectively with an experimentally determined mean value of 2.26 mg/ml. Microbial biomass production (MBP) varied (P<0.0001) between 16.2 and 46.5 mg per 100 mg of true degraded substrate (TSD) and gas volumes and MBP were inversely (P<0.0001) associated when related to a unit of TSD. The inverse relationship found for proportional gas volume and proportional MBP shows that gas volume measurements give only incomplete information about fermentation. More information was obtained by combining gas volume measurements with a determination of TSD by treatment of the incubation residue with neutral detergent solution (NDS). It is recommended to study substrate-specific differences in the partitioning of fermentation products at similar microbial growth phases. However, NDS treatment was found to be unsuitable for starchy concentrates and also for tannin-rich browses. Except for these feeds microbial biomass production can be estimated as: MBP = TSD - (gas volume x SF). These in vitro estimates were in acceptable agreement with in vivo findings in goats, sheep and cattle.

Technical Abstract: A theoretical model of the relationship between the rumen fermentation products short chain fatty acids (SCFA), microbial biomass and gases is presented and contrasted with in vitro and in vivo findings. A very close relationship was established between SCFA and gas production that allowed the calculation of a stoichiometrical factor (SF) to convert gas volumes into carbon, hydrogen and oxygen requirements for the production of a unit volume of gas. The range in SF values was 2.20 and 2.34 mg/ml for high acetate and high propionate fermentation, respectively with an experimentally determined mean value of 2.26 mg/ml. Microbial biomass production (MBP) varied (P<0.0001) between 16.2 and 46.5 mg per 100 mg of true degraded substrate (TSD) and gas volumes and MBP were inversely (P<0.0001) associated when related to a unit of TSD. The inverse relationship found for proportional gas volume and proportional MBP shows that gas volume measurements give only incomplete information about fermentation. More information was obtained by combining gas volume measurements with a determination of TSD by treatment of the incubation residue with neutral detergent solution (NDS). It is recommended to study substrate-specific differences in the partitioning of fermentation products at similar microbial growth phases. However, NDS treatment was found to be unsuitable for starchy concentrates and also for tannin-rich browses. Except for these feeds microbial biomass production can be estimated as: MBP = TSD - (gas volume x SF). These in vitro estimates were in acceptable agreement with in vivo findings in goats, sheep and cattle.

Last Modified: 12/20/2014
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