Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


School of Animal Science

First Advisor

Donald L. Thompson, Jr


Three experiments were designed to provide a comprehensive reference for the responses of plasma metabolites and hormones to control and restricted intakes of protein and(or) energy and to feed deprivation. The objectives of the first and second experiments were to characterize the effects of protein and(or) energy restriction on glucose, insulin, nonesterified fatty acids (NEFA), urea nitrogen (N), insulin like growth factor-1 (IGF-1), cortisol, triiodothyronine ($T\sb3$, thyroxine ($T\sb4$), prolactin, and growth hormone (GH) concentrations in plasma on a daily basis, after feeding, and after i.v. administration of glucose or epinephrine. The third experiment was conducted to answer questions of how these plasma constituents, plus $\beta$-hydroxybutyrate, lactate, and glucagon, respond to feed deprivation and exercise. In the first experiment, energy restriction increased daily plasma concentrations of NEFA (P =.0001) and urea N (P =.013), whereas protein restriction decreased (P =.002) urea N concentrations. Restriction of protein and(or) energy reduced (P =.0001) plasma IGF-1 concentrations. These effects of protein and energy restriction occurred within 24 h of dietary initiation and were consistent (day effect, P $>$.1) throughout the experiment. Plasma NEFA concentrations were altered by energy restriction during feeding (energy x time, P =.005) and the epinephrine challenge (energy x time, P =.06). Protein restriction increased (P =.09) GH episodes during a 14 h feeding period. In the second experiment, immediate responses of a dietary switch were observed for NEFA (control to restricted; time x diet interaction, P =.009; restricted to control; time x diet interaction, P =.04). In the third experiment, feed deprivation elevated plasma NEFA, $\beta$-hydroxybutyrate, urea N, glucagon, and cortisol (day x diet, P $<$.1), and reduced IGF-1 (day x diet, P =.04) concentrations. Feed deprivation increased the plasma glucose (time x diet, P =.07) and prolactin (time x diet, P =.09), and decreased the NEFA (time x diet, P =.006) response to exercise. It was concluded that metabolic and hormonal responses occur within 24 h of dietary changes and that plasma constituents are altered by protein and(or) energy restriction during feeding, glucose, and epinephrine challenges, and also by feed deprivation on a daily basis and during exercise.