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An integrated, dynamic model of feed hydration anddigestion, and subsequent bacterial mass accumulation in the rumen

Published online by Cambridge University Press:  09 March 2007

Jaap Van Milgen ,
Larry L. Berger  and
Michael R. Murphy
Jaap Van Milgen
Affiliation:
Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801, USA
Larry L. Berger
Affiliation:
Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801, USA
Michael R. Murphy
Affiliation:
Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801, USA
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Abstract

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Hydration of feeds and bacterial attachment to feed particles are thought to play major roles in rumen digestion of fibrous feedstuffs. The objective of the present study was to integrate these phenomena in a mechanistic model that could be used for data analysis. The proposed model was based on the conversion of biomass, where digestion end-products can be used for the synthesis of bacterial mass. Digestion of the potentially digestible fraction and subsequent accumulation of bacterial mass was based on a sequential, three-compartment model. These compartments represented substrate undergoing hydration, digestion, and bacterial mass accumulation. A fraction of the substrate was used for synthesis of bacterial mass. It was assumed that these bacteria associate either temporarily or permanently with the remaining substrate. Dacron bags containing either dry or fully-hydrated lucerne (Medicago sativa), maize (Zea mays) cobs, orchard grass (Dactylis glomeratd), and wheat straw were incubated in the rumen of a steer that was infused continuously with (15NH4)2SO4. The 15N-enrichments of isolated particle-associated bacteria and residue remaining in the bags were used to estimate bacterial attachment. Substrate remaining and microbial mass accumulation were analysed simultaneously. Hydration did not appear to limit digestion. Fractional rate of digestion and appearance of attached bacterial mass was fastest for lucerne. For lucerne, 5 % of the digestion end-products were used for synthesis of bacteria that associated with the substrate, whereas for maize cobs, orchard grass, and wheat straw this was 16, 14, and 19% respectively. Less than 2% of digestion end-products were used for synthesis of bacteria that permanently remained associated with the substrate. Permanent association can occur only with the indigestible fraction, and probably represents bacterial debris. Lysis and/or detachment of bacterial cells was highest for lucerne, and was indicative of the rapid dynamics of lucerne digestion.

Keywords

ModelsBacterial attachmentRumen digestion
Type
Modelling Feed Intake, Digestion and Rumen Bacteria
Information
British Journal of Nutrition , Volume 70 , Issue 2 , September 1993 , pp. 471 - 483
Copyright
Copyright © The Nutrition Society 1993

References

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