Simulation analysis of substrate utilization in the mammary gland of lactating cows

A kinetic modelling approach was developed and investigated with the aim of predicting the utilization of major substrates in the mammary gland and mi lk secretion rates in the lactating cow at varying concentrations of substr ate in arterial blood. The model includes kinetic equations of transport an d metabolism of glucose, acetate, free amino acids and free fatty acids in secretory cells and a phenomenological description of autoregulation of loc al blood flow, in which an energy criterion of control has been used. The p redicted relationships between the rate of milk secretion and glucose level s in the blood are consistent with experimental results. Differential stimu lation of alpha-lactalbumin synthesis causes increments in local blood flow and milk secretion rate in the model. The results of the study suggest tha t there is no simple relationship between the level of substrates in the bl ood and milk yield and contents of fat and protein in milk. This is because the effect on production of varying patterns of substrate concentrations i n the blood is mediated by network interactions at the level of secretory c ell metabolism and microcirculation. However, dynamic modelling provides a rational framework for developing such predictive tools.