Gluconeogenesis is a process of major physiological importance in all species, especially in lactating ruminants. The long-term objective of this project is to quantitate the carbon sources contributing to the total glucose utilized by ruminants in various dietary and physiological states. Our "standard" animals, chosen to minimize physiological variables, are 160-205 kg calves fed a high-grain ration every 2 hours in amounts which will promote slow growth. Our first step was to determine glucose turnover rates in these calves, and this has been accomplished for our initial diet and conditions. Next, we found that less than 10% of the total glucose turnover is accounted for by absorbed glucose, indicating that gluconeogenesis must account for over 90% of the glucose utilized. During the past year, we have studied propionate production rates in the rumen and studied the repeatability and reliability of techniques. Studies have been initiated to quantitate the contribution of absorbed propionate to gluconeogenesis and subsequent glucose turnover. Preliminary calculations suggest that slightly over 50% of the glucose arises from propionate. During 1976, we will continue to study the contribution of propionate to gluconeogenesis and will begin to explore the contribution of amino acids, especially alanine, to ruminant gluconeogenesis. BIBLIOGRAPHIC REFERENCE: Schmidt, S. P., J. A. Smith and J. W. Young. Rapid determination of (carbon-14) glucose specific radioactivity for in vivo glucose kinetics. J. Dairy Sci. 58:952-956. 1975.