The Journal of Nutrition Vol. 127 No. 6 June 1997, pp. 1243-1252
Copyright ©1997 by the American Society for Nutritional Sciences

Evaluation of a Model Integrating Protein and Energy Metabolism in Preruminant Calves

Manuscript received 30 April 1996. Initial reviews completed 18 June 1996. Revision accepted 21 January 1997.

Walter J. J. Gerrits^*, , James France, Jan Dijkstra, Marlou W. Bosch, G. Henk Tolman, and Seerp Tamminga

^* Wageningen Institute of Animal Sciences, Wageningen Agricultural University, 6700 AH, Wageningen, The Netherlands;  Institute of Grassland and Environmental Research, North Wyke, Okehampton, EX20 2SB, UK; and  T.N.O. Nutrition and Food Research Institute, Department of Animal Nutrition and Meat Technology (ILOB), 6700 AA, Wageningen, The Netherlands

In a companion paper, a mechanistic model is described, integrating protein and energy metabolism in preruminant calves of 80-240 kg live weight. The model simulates the partitioning of nutrients from ingestion through intermediary metabolism to growth, consisting of accretions of protein, fat, ash and water. The model also includes a routine to check possible dietary amino acid imbalance and can be used to predict amino acid requirements. This paper describes a sensitivity and behavioral analysis of the model, as well as tests against independent data. Increasing the carbohydrate:fat ratio at equal gross energy intakes leads to higher simulated protein- and lower simulated fat-deposition rates. Simulation of two experiments, not used for the development of the model, showed that rates of gain of live weight, protein and fat were predicted satisfactorily. The representation of protein turnover enables the investigation of the quantitative importance of hide, bone and visceral protein in protein and energy metabolism. The model is highly sensitive to 25% changes in kinetic parameters describing muscle protein synthesis and amino acid oxidation. Comparing simulated with experimentally derived amino acid requirements shows agreement for most amino acids for calves of ~90 kg live weight. For calves of ~230 kg live weight, however, lower requirements for lysine and 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.

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