Modelling volatile fatty acid dynamics and rumen function in lactating cows

262 Pages·2007·2.28 MB·English

by  André Bannink

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Modelling Volatile Fatty Acid Dynamics
and Rumen Function
in Lactating Cows
Promotoren
Prof. dr. ir. S. Tamminga
Emeritus Hoogleraar in de Diervoeding
Leerstoelgroep Diervoeding
Wageningen Universiteit

Prof. dr. J. France
Professor and Canada Research Chair in Integrative Modelling
Department of Animal and Poultry Science
University of Guelph
Guelph, Canada

Co-promotor
Dr. ir. J. Dijkstra
Universitair Docent
Leerstoelgroep Diervoeding
Wageningen Universiteit

Promotiecommissie
Prof. dr. ir. O. Oenema, Wageningen Universiteit
Prof. dr. J. Molenaar, Wageningen Universiteit
Prof. dr. G.J. Schaafsma, Wageningen Universiteit
Dr. E. Kebreab, University of Manitoba, Canada

Dit onderzoek is uitgevoerd binnen de onderzoeksschool Wageningen Institute of Animal
Sciences (WIAS)
Modelling Volatile Fatty Acid Dynamics
and Rumen Function
in Lactating Cows

André Bannink

Proefschrift
ter verkrijging van de graad van doctor
op gezag van de rector magnificus
van Wageningen Universiteit,
prof. dr. M.J. Kropff,
in het openbaar te verdedigen
op maandag 26 november 2007
des namiddags te vier uur in de Aula
Bannink, A.
Modelling volatile fatty acid dynamics and rumen function in lactating cows
PhD Thesis, Wageningen University, The Netherlands
With references – With summary in English and Dutch

ISBN: 978–90–8504–785-8
Abstract

Bannink, A., 2007. Modelling Volatile Fatty Acid Dynamics and Rumen Function in
Lactating Cows. PhD Thesis, Wageningen University, The Netherlands

Mathematical models are developed to quantity and integrate the various processes
involved with rumen fermentation. Three extant mechanistic models of rumen
fermentation were studied (Baldwin et al., 1987; Danfær, 1990; Dijkstra et al., 1992), each
with a truly dynamic representation but different conceptual approach. The models were
compared on mathematical representation of individual processes and their prediction
accuracy was evaluated. Although the models predicted similar rates of substrate
degradation and rumen outflow of organic matter, total crude protein and microbial
protein, they differed substantially in representation of the underlying microbial
mechanisms. The model of Baldwin et al. (1987) performed best in prediction of the
combination of rumen pool sizes and duodenal flows, whereas the model of Dijkstra et al.
(1992) was evaluated to deliver the most realistic outflow of rapidly fermentable
carbohydrates. Further, it was identified that all models needed improvement with respect
to the prediction of amounts and type of volatile fatty acids (VFA) produced. In a
subsequent evaluation it was investigated to what extent individual model elements, of a
selection of five, could be responsible for inaccurate VFA predictions. The results
suggested that inaccuracy of stoichiometric coefficients of VFA yield from fermented
substrate (VFA coefficients) and incorrect representations of VFA absorption kinetics are
the most likely causes. New values of VFA coefficients were derived by regression of a
stoichiometric model of VFA yield against data of VFA molar proportions observed in
vivo in rumen fluid of lactating cows. Inputs to the model were observed rates of rumen
substrate degradation. Regression against simulated data sets including random error
indicated that the accuracy of this method to estimate VFA coefficients is acceptable.
Estimates from regressions against in vivo data delivered new sets of VFA coefficients for
roughage-rich and concentrate-rich diets. In a follow-up study the representation of
stoichiometry was made pH-dependent. With regression of this model against in vivo data
a profound effect of rumen pH on the type of VFA formed from rapidly fermentable
carbohydrates was established. Besides VFA production, the rumen concentrations and the
amount and profile of VFA available for the cow are also affected by absorption and
metabolism of VFA by epithelial tissues in the rumen wall. A mechanistic model was
constructed that represents the dynamics of these processes, including the effects of
changes in VFA concentration differences between different compartments, the effect of
competitive inhibition between VFA and the effect of changes in surface area and
epithelial mass. Although some essential characteristics of VFA transport and intra-
epithelial metabolism could be reproduced by the model, it was concluded that there is a
definite need for more experimental data. Various levels of aggregation need to be
included when representing whole rumen function. Besides intrinsic degradation
characteristics and passage of ingested substrates, environmental conditions in the rumen
and functionality of the rumen wall need to addressed.

Keywords: Dynamic modelling, Rumen fermentation, Volatile fatty acids, Rumen
absorption, Epithelial metabolism, Rumen wall, Lactating cows

Table of contents

Chapter 1 Introduction to rumen function 1

Chapter 2 Impact of diet-specific input parameters on simulated rumen
Function 15

Chapter 3 Comparison of mechanistic rumen models on mathematical
formulation of extra-microbial and microbial processes 45

Chapter 4 Comparison and evaluation of mechanistic rumen models 81

Chapter 5 Causes of inaccurate prediction of volatile fatty acids by
simulation models of rumen function in lactating cows 109

Chapter 6 Estimation of the stoichiometry of volatile fatty acid production
in the rumen of lactating cows 133

Chapter 7 Modelling the implications of feeding strategy on rumen
fermentation and functioning of the rumen wall 165

Chapter 8 General discussion 195

Summary & Samenvatting 233

Dankwoord / Acknowledgement 249

Curriculum Vitae 251

Chapter 1

Introduction to Rumen Function