Fermentation Balance Approach to Estimate Extent of Fermentation and Efficiency of Volatile Fatty Acid Formation in Ruminants

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Abstract
A fermentation balance equation was used to estimate the extent of fermentation of rations fed at or near voluntary intake to lactating" dairy cows. The rations va.ried in hay to concentrate ratio from 100:0 to 20:80 and in four trials the high concen- trate ration was fed completely pelleted. The extent of fermentation varied from 71% on the hay ration to 40% on the com- pletely pelleted high concentrate ration. The factors affecting extent of fermenta- tion were: 1) The hay to concentrate ratio, 2) fineness of particles, and 3) level of intake. The residual heat of fermentation was 6.4% of fermented substrate, and the theoretical CO../CH, ratio increased with increasing concentrate in the diet. The assumptions involved in these computations and the implications of the results obtained on efficiency of fermentation and feed ef- ficiency for rurninants were discussed. It has been suggested (28) and further dis- cussed (14) that the extent to which ruminant diets are fermented could be estimated using" information derived from the level of methane production and the proportions of volatile fatty acid (¥FA) produced during the fermentation. This approach is indirect, but can be made without surgical interference involving cannula- tion needed for the more direct approach. In this paper the results of using' a fermenta- tion balance will be given and the most obvious assumptions involved will be discussed. The data were obtained from energy balance ex- periments that have been carried out with dairy cows at the Energy Metabolism Laboratory in Beltsville (8, 10). Measurements The daily intake of digestible carbohydrate, the methane production, the metabolizable en- ergy and the heat production measured with mature Kolstein cows were taken from (8) and