A novel model to explain dietary factors affecting hypocalcaemia in dairy cattle

Most dairy cows exhibit different degrees of hypocalcaemia around calving because the gestational Ca requirements shift to the disproportionately high Ca requirements of lactation. Ca homeostasis is a robust system that effectively adapts to changes in Ca demand or supply. However, these adaptations often are not rapid enough to avoid hypocalcaemia. A delay in the reconfiguration of intestinal Ca absorption and bone resorption is probably the underlying cause of this transient hypocalcaemia. Several dietary factors that affect different aspects of Ca metabolism are known to reduce the incidence of milk fever. The present review describes the interactions between nutrition and Ca homeostasis using observations from cattle and extrapolations from other species and aims to quantitatively model the effects of the nutritional approaches that are used to induce dry cows into an early adaptation of Ca metabolism. The present model suggests that reducing dietary cation–anion difference (DCAD) increases Ca clearance from the blood by dietary induction of systemic acidosis, which results in hypercalciuria due to the loss of function of the renal Ca transient receptor potential vanilloid channel TRPV5. Alternatively, reducing the gastrointestinal availability of Ca by reducing dietary Ca or its nutritional availability will also induce the activation of Ca metabolism to compensate for basal blood Ca clearance. Our model of gastrointestinal Ca availability as well as blood Ca clearance in the transition dairy cow allowed us to conclude that the most common dietary strategies for milk fever prevention may have analogous modes of action that are based on the principle of metabolic adaptation before calving

The Marginal Utility of Medical Resources in Clinics with Deterministic Patient Arrivals: A Simulation Study

In recent years, dramatic increase in the cost of health care has compelled practitioners to draw a balance between improving efficiency and reducing costs. A discrete-event simulation model has been constructed to assist a typical two-physician family practice healthcare clinic in evaluating potential resource allocations to improve operating efficiencies and patient satisfaction. A performance measure, constructed on a monetary scale (dollars/day), strives to simultaneously satisfy the conflicts of patients, medical staff, and clinic owners by capturing system dynamics. Utility of medical resources is studied from the point of view of a local two-physician nephrology clinic in the light of resource flexibility, resource scheduling, and resource allocation to arrive at an ‘efficient utility frontier’, a reflection of patient satisfaction