A DYNAMIC, MECHANISTIC MODEL OF METABOLISM IN ADIPOSE TISSUE OF LACTATING DAIRY CATTLE

Abstract Text: Research in dairy cattle biology has resulted in a large body of knowledge on nutrition and metabolism supporting and underlying milk production and efficiency.   The adipose tissues are an essential part of the overall efficiency of dairy cattle.  Therefore we constructed a dynamic, mechanistic model of control of metabolism in the adipose tissues of dairy cattle. The model describes the biochemical interconversion of glucose, acetate, glycerol, fatty acids, and triacylglycerols. Data from our own research and published references were used to set equation forms and parameter values. Metabolites are absorbed from blood, and fatty acids are activated to the Acyl CoEnzymeA counterparts.  Fatty acids are partitioned to palmitic, stearic, oleic and linoleic acids. Enzymatically catalyzed reactions are explicitly described with parameters including maximal velocity and substrate sensitivity.  Energetic stoichiometry is maintained by the balance of ATP utilizing and generating reactions.  Changes in gene transcription or post-translational modification of enzyme activity control nutrient metabolism, including control by insulin and norepinephrine. The model behavior to availability of nutrients and insulin or norepinephrine is in agreement with published data. For example, triacylglycerol synthesis when glucose is low (1 mM) is 17.82 + 1.9 X ln (Fatty Acyl CoA); when glucose is high (5 mM) it is 44.96 + 5.67 ln(Fatty Acyl CoA).  Triacylglycerol lipolysis is -13.28 - 4.33 ln (Fatty Acyl CoA)) when norepinephrine is low, and is - 22.14 - 7.22 ln (Fatty Acyl CoA) when it is high (25 % more than basal). This model can form a basis for more sophisticated integration of existing knowledge and future studies on metabolic efficiency of dairy cattle.

Keywords: adipose, metabolism, mechanistic model, lactation