EVALUATION OF A MODEL INTEGRATING PROTEIN AND ENERGY-METABOLISM IN PRERUMINANT CALVES

In a companion paper, a mechanistic model is described, integrating pr otein and energy metabolism in preruminant calves of 80-240 kg live we ight. The model simulates the partitioning of nutrients from ingestion through intermediary metabolism to growth, consisting of accretions o f protein, fat, ash and water. The model also includes a routine to ch eck possible dietary amino acid imbalance and can be used to predict a mino acid requirements, This paper describes a sensitivity and behavio ral analysis of the model, as well as tests against independent data. Increasing the carbohydrate:fat ratio at equal gross energy intakes le ads to higher simulated protein- and lower simulated fat-deposition ra tes. Simulation of two experiments, not used for the development of th e model, showed that rates of gain of live weight, protein and fat wer e predicted satisfactorily. The representation of protein turnover ena bles the investigation of the quantitative importance of hide, bone an d visceral protein in protein and energy metabolism, The model is high ly sensitive to 25% changes in kinetic parameters describing muscle pr otein synthesis and amino acid oxidation. Comparing simulated with exp erimentally derived amino acid requirements shows agreement for most a mino acids for calves of similar to 90 kg live weight. For calves of s imilar to 230 kg live weight, however, lower requirements for lysine a nd for methionine + cystine are suggested by the model. More attention has to be paid to the inevitable oxidative losses of amino acids, It is concluded that the model provides a useful tool for the development of feeding strategies for preruminant calves in this weight range.