MATHEMATICAL-MODELING OF METABOLIC-REGULATION AND GROWTH

Two problems related to the mathematical modelling of animal growth were pointed out: (1) What are the physiological mechanisms determining sigmoid growth, and how can sigmoid growth curves be simulated by mechanistic principles? (2) Intracellular substrates are partitioned between different metabolic pathways. How is this partition regulated, and how can it be simulated? Two dynamic and mechanistic research models were constructed in order to elucidate these problems. The objective of model 1 was to test if a sigmoid growth curve could be simulated by mechanistic rate equations describing protein synthesis and degradation and without any definition of mature size. The objective of model 2 was to simulate metabolic control of substrate partition between synthetic and oxidative transactions using a principle of allosteric enzyme regulation. Results of simulation showed that both objectives were achieved: with model 1 sigmoid growth curves were simulated in agreement with literature data, and model 2 was able to regulate the rate of body mass retention and the use of nutrients for either synthesis or oxidation in response to a wide range of different feed intakes. By means of the simulated regulations, the intracellular levels of nutrients and metabolic energy could be maintained, and the rate of energy yield by oxidation was in all situations equal to the rate of energy usage for maintenance and growth. The need for physiological and biochemical knowledge in modelling animal performance and the potential benefits of such models in animal science are briefly discussed.