In vivo kinetic techniques were used to quantify changes in metabolism of propionate, glucose, and blood CO2 when glucose was infused intravenously at 0, 342, or 737 g/d into four lactating cows. Neither production of milk or milk fat nor composition of milk was changed. Production of milk protein increased for the high glucose treatment. Isotope dilution data were used to calculate irreversible losses of rumen propionate, plasma glucose, and blood CO2 and to determine a unique solution for flux of C in this three-pool system. Irreversible losses of propionate and CO2 were not changed. Infusions of glucose increased irreversible loss of glucose in proportion to amounts infused, thus indicating there was no change in endogenous production of glucose. For the control, 52% of the C flux of blood glucose was derived directly from rumen propionate and another 26% came from other gluconeogenic substrates. Flux of C into glucose from exogenous sources increased in proportion to amounts of glucose infused. Flux of C from rumen propionate remained constant. The rate of C leaving the glucose pool, other than as CO2, tended to increase with infusion of glucose, and oxidation of glucose tended to increase for the high glucose treatment. High producing cows adjusted to increased exogenous glucose by increasing glucose utilization and without decreasing endogenous glucose production.

Igniting excitement for physics in our students is a goal of every instructor. In this paper, we discuss a unique example of the concept of density, a subject that is rarely viewed as intriguing by students. By combining a problem involving dinosaurs and an effective density, our students’ interest is often captured through calculating an estimated mass of hatchling tyrannosaur and sauropod dinosaurs. This unusual kind of density also provides an interesting backdrop for students to test their understanding of density. We also discuss how this result can be used to learn more about dinosaurs.

Exciting examples of physics principles illuminate the power and scope of our discipline. In this paper, we discuss a conservation of energy example for an introductory course. Energy conservation is applied to bird and dinosaur eggs to derive a method to predict the incubation period and the embryonic metabolism solely from the egg geometry. The power of this fundamental principle to yield insights into a biological example helps to demonstrate the utility of conservation of energy.