Modelling of magnesium metabolism in ruminants

Abstract

A model of magnesium metabolism in sheep is proposed. It is based on standard Michaelis-Menten enzyme kinetics to describe the transport of magnesium across the rumen wall and passive diffusion for the absorption of magnesium in the hindgut. Factors known to have an effect on magnesium metabolism in farm animals, namely the concentrations of potassium and magnesium in the diet, and the physico-chemical conditions within the rumen as determined by the type of the diet, are incorporated into the model. Consideration of the rumen as the only site of magnesium absorption provided an inadequate mechanistic description of magnesium metabolism in sheep. To ensure compatibility between predicted magnesium absorption and recent independent data sets for magnesium balances, it was necessary to include in the model aspects of magnesium absorption that operate in the hindgut. The results from this model suggest that there is need for a series of experiments to determine magnesium transport in the hindgut of sheep.

A section of the model deals with the transport of magnesium between plasma and the cerebrospinal fluid. Results from the model were in reasonable agreement with recent experimental data, but only after parametric values for cerebrospinal fluid volume fractional turnover rates were changed substantially from 7.2 to 0.25.

The possibility of bone acting as a reservoir of magnesium to assist in whole animal magnesium homeostasis was considered and shown to be quantitatively insignificant.

A series of experiments is proposed to challenge the model and to estimate the values of parameters used.