METABOLIC RELATIONSHIPS IN THE SUPPLY OF NUTRIENTS FOR MILK PROTEIN-SYNTHESIS - INTEGRATIVE MODELING

The objective of research under the NC-185 regional project is to iden tify the critical chemical transformations in the rumen, digestive tra ct, gastrointestinal and splanchnic tissues, and adipose and mammary t issues that define patterns of nutrient utilization in lactating dairy cows. This objective includes research on differences in fermentation , digestion, absorption, and tissue utilization of nutrients in suffic iently different situations to permit estimation of parameters definin g various nutrient interconversions. The regional project is utilizing dynamic, mechanistic models of metabolism as tools for integrative an alyses of experimental data generated by the group. During the early p hases of the project emphasized herein, primary emphasis was on develo pment of models of adipose tissue, mammary gland, liver, rumen, and wh ole animal metabolism. Serious inadequacies exist in the detail and sc ope of knowledge of rates of chemical transformations across the wide range of milk yields and nutrient intakes found in production situatio ns. Current knowledge, as described in the various equations and param eters in the models, is presented and discussed. Some characteristics of the current models are illustrated, and methods to utilize the mode ls to identify important experiments are discussed. More cooperative e fforts are necessary, including experimental designs that focus on qua ntification of relationships between input and output, physiological m echanisms that alter patterns of nutrient utilization in lactating dai ry cows, and yield estimates of the parameters describing the pre- and postabsorptive uses of feed nutrients.