Simulation of nutrient digestion, absorption and outflow in the rumen: model description
Catherine
Lloyd
Auckland Bioengineering Institute, The University of Auckland
Model Status
This CellML model runs in both OpenCell and COR. The units have been checked and they are consistent. In order to balance the units in a couple of equations a "balancing factor" had to be introduced (eqs 4.13 and 14.36). Also note there are two typographical errors in the published paper: eq 1.1 should be C_Pd = Q_Pd/V_Ru (not C_Pd = Q_Pd*V_Ru) and eq 8.2 P_Fu_InFu = Y_Fu_InFu*D_Fu (not P_Fu_InFu = U_Fu_InFu*D_Fu). Finally there are quite a few variables with undefined values. To complete the CellML model, where parameter values were missing, a value of 1.000 has been used. Note that there are some genuine values of 1. These have been entered as just 1 or 1.0. The model simulation output looks reasonable, but with no results figures in the published paper it is hard to say whether or not the CellML model accurately recreates the published results.
Model Structure
ABSTRACT: A mathematical model is described that stimulates the digestion, absorption and outflow of nutrients in the rumen. The model consists of 17 state variables, representing nitrogen, carbohydrate, lipid, microbial and volatile fatty acid pools. The flux equations are described by Michaelis-Menten or mass action forms with model_parameters calculated from the literature. Several specific areas of improvement in representation of rumen processes were reconsidered during model development. These included microbial substrate preference, differential outflow and chemical composition of rumen microbes, recycling of microbial matter within the rumen, uncoupling of fermentation with respect to nitrogen availability, reduced microbial activity at reduced rumen pH and pH-dependent absorption of volatile fatty acids and ammonia. The model was used to examine the effects of the diet on the profile of nutrients available for absorption and was shown to respond appropriately to different intake and nitrogen levels. The validity of the improvements and the predictions of nutrient supply on a variety of dietary inputs are tested in a companion paper.
The original paper reference is cited below:
Simulation of nutrient digestion, absorption and outflow in the rumen: model description, Dijkstra J, Neal HD, Beever DE, and France J, 1992, The Journal of Nutrition, 122, 2239-2256. PubMed ID: 1331382
Diagrammatic representation of the rumen model. Purple boxes indicate state variables and arrows indicate fluxes.
Q_Pd
degradable protein pool
Q_Ps
soluble protein pool
Q_Pu
undegradable protein pool
Q_Am
ammonia pool
Q_Li
lipid pool
Q_Sd
degradable starch pool
Q_Fd
degradable fiber pool
Q_Fu
undegradable fiber pool
Q_Ha
hexose availability to amylolytic microbes
Q_Hc
hexose availability to fibrolytic microbes
Q_Ma
amylolytic microbes pool
Q_As
microbial storage polysaccharides pool
Q_Mc
fibrolytic microbes pool
Q_Ac
aceitic acid pool
Q_Pr
propionic acid pool
Q_Bu
butyric acid pool
Q_Vl
valeric acid pool
Lloyd
Catherine
May
c.lloyd@auckland.ac.nz
The University of Auckland
Auckland Bioengineering Institute
2010-05-28
rumen
keyword
metabolism
digestion
1331382
Dijkstra
J
Neal
H
D
Beever
D
E
France
J
Simulation of nutrient digestion, absorption and outflow in the rumen: model description
1992-11
The Journal of Nutrition
122
2239
2256