Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2001
Publication Date: 6/1/2001
Citation: BLUMMEL, M.R., GRINGS, E.E., MOSS, A.R., GIVENS, D.I. A MECHANISTIC APPROACH TO THE ESTIMATION OF INTAKE OF RUMINANTS BY METHANE EXCRETION AND IN VITRO FERMENTATION CHARACTERISTICS. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2001. v. 79(Suppl. 2). p. 137. Interpretive Summary: Methane measurements in vivo in combination with measurements of in vitro fermentation characteristics such as short chain fatty acids proportions and efficiencies of microbial production provide a promising check for intake estimates based on marker techniques. This approach has also considerable potential for studying carbon efficiencies in grazing ruminants. Methane production, a waste product of ruminal forage conversion, can be contrasted with the generation of useful products, short chain fatty acids and microbial biomass. As seen, the proportional production of both short chain fatty acids and microbial biomass varies considerably. The relative requirement of animals for energy (short chain fatty acids) and protein (microbial biomass) is a function of the physiological status of the animal. Integration of these aspects can help optimize the generation of useful products while reducing the production of waste products.
Technical Abstract: The accuracy of calculating organic matter intake by methane (CH4) production in vivo together with in vitro fermentation characteristics was examined for 15 roughages offered to sheep ad libitum. Methane production was measured by open circuit calorimetry and organic matter intake (OMI) and in vivo digestibility measurements were obtained in metabolic cages. In vitro roughage fermentation characteristics examined were total and proportional short chain fatty acid (SCFA) production, the efficiency of microbial biomass production (EMP), true substrate degradability, and gas production. These variables were used together with stoichiometrical principles of rumen fermentation to compare measured and calculated OMI. Measured OMI and methane production were related (R**2 = 0.86, P < 0.0001) but CH4 production per kilogram organic matter digested in vivo varied significantly (P < 0.05) between roughages. By using CH4 production, in vitro digestibility measurements and various constant values for SCFA proportions (0.7: 0.2: 0.1; 0.6: 0.3: 0.1; 0.5: 0.4: 0.1) for the acetate: propionate: butyrate ratio and for the efficiency (0.2 and 0.4) of microbial production a maximum R**2 of 0.58 was obtained for the relationship between measured and calculated OMI. By measuring the actual in vitro SCFA proportions and EMP, this R**2 could be improved to 0.79 depending which in vitro technique was employed for the estimations of EMP.