A kinetic modelling approach was developed and investigated with the
aim of predicting the utilization of major substrates in the mammary gland and milk
secretion rates in the lactating cow at varying concentrations of substrate in arterial
blood. The model includes kinetic equations of transport and metabolism of glucose,
acetate, free amino acids and free fatty acids in secretory cells and a phenomenological
description of autoregulation of local blood flow, in which an energy
criterion of control has been used. The predicted relationships between the rate of
milk secretion and glucose levels in the blood are consistent with experimental
results. Differential stimulation of α-lactalbumin synthesis causes increments in local
blood flow and milk secretion rate in the model. The results of the study suggest that
there is no simple relationship between the level of substrates in the blood and milk
yield and contents of fat and protein in milk. This is because the effect on production
of varying patterns of substrate concentrations in the blood is mediated by network
interactions at the level of secretory cell metabolism and microcirculation. However,
dynamic modelling provides a rational framework for developing such predictive
tools.