A STUDY OF GLUCOSE METABOLISM AND KETOSIS DEVELOPMENT IN PERIPARTURIENT COWS USING A MECHANISTIC MODEL

Abstract

Periparturient cows are susceptible to ketosis. An animal trial was conducted to evaluate the effect of a transition diet on production performance and ketone body (KB) accumulation. The transition diet was fed from 14 days before expected parturition to 14 days after calving. The energy density and nonstructural carbohydrate content in the transition diet was lower compared to the lactation diet, but higher compared to the non-lactating cow diet. Production performance was not affected by transition diet. Plasma glycerol may be an important contributor to gluconeogenesis during the periparturient period. Feeding a transition diet around parturition was associated with greater mobilization of adipose tissue and greater exposure to KB in early lactation. Data from the animal trial were used to develop a mechanistic model to quantify the interrelationship between glucose and lipid metabolism in periparturient cows. The driving variables of the model were dry matter intake, feed composition, calf birth weight, milk production, and milk components. The response variables were body fat content and concentrations of plasma glucose, glycerol, nonesterified fatty acids and total KB. Comparison of model predictions to data collected in an independent experiment revealed that the model over-predicted glucose and KB concentrations by 0.62 and 0.37 mM, respectively. Calf birth weight, dry matter intake, milk yield, and body condition score were increased by one standard deviation to estimate the model response in KB formation. The responses to the increases in the model parameters (e.g. the rate of fat mobilization) were evaluated to identify the likely critical control points in the animal. The model demonstrated that utilization rate of nonesterified fatty acids has a greater impact on KB concentrations in the first few days of lactation than the other parameters tested in the model. Glucose deficiency was closely related to the rate of fat mobilization. And, the excessive KB could result from elevated fat mobilization for glycerol to compensate for the negative glucose balance in periparturient cows. It is important to avoid overfeeding during the pre-lactation period to prevent ketosis development.