Modelling mammary metabolism in the dairy cow to predict milk constituent yield, with emphasis on amino acid metabolism and milk protein production: Model construction

Hanigan, MD Crompton, LA Metcalf, JA France, J

Md. Hanigan et al., Modelling mammary metabolism in the dairy cow to predict milk constituent yield, with emphasis on amino acid metabolism and milk protein production: Model construction, J THEOR BIO, 213(2), 2001, pp. 223-239

45

INGLESE

Article

Multidisciplinary

JOURNAL OF THEORETICAL BIOLOGY

0022-5193 → ACNP

213

2

2001

223 - 239

ISI

0022-5193(20011121)213:2<223:MMMITD>2.0.ZU;2-L

Previous efforts to simulate mammary metabolism have focused on energy, mos tly considering amino acids (AA) in aggregate. The main objective of this w ork was to build a model of mammary metabolism, based on data from arterio- venous difference studies, which considered AA in sufficient detail to pred ict yields of milk solids. The model contains 19 state variables and consid ers the removal of 37 metabolites from blood, including 22 AA. It is driven by blood flow and arterial concentrations, and outputs include milk protei n, milk lactose, and three classes of milk fat (by chain length). The model was parameterized using a balance version of it and the mean observations from four arterio-venous difference experiments, with a limited number of a ssumptions, and evaluated against these experiments. In assembling the bala nce model, milk protein output was not predicted satisfactorily, as some es sential AA were not present in quantities great enough to support the rates of milk protein synthesis observed experimentally. Tryptophan showed the g reatest deficit, followed by tyrosine plus phenylalanine, methionine, and h istidine. In addition, significant quantities of pyruvate were needed to sy nthesize serine, glycine, and alanine. The supply of a-ketoglutarate plus g lutamate to synthesize proline and glutamine was provided in part by catabo lism of arginine; the remainder was derived from catabolism of other AA and energetic substrates. (C) 2001 Academic Press.