Nutritional Regulation of Milk Fat and Protein Synthesis

Hatch (project ILLU-538-307)

Objectives: The overall objective is to characterize nutrient-gene interactions during milk fat and protein synthesis. We will use genomic analysis along with blood metabolites/hormones and milk composition to identify nutrient-regulated genes that may play crucial roles during milk fat and protein synthesis. Our hypothesis is that cells in the mammary gland possess homeostatic regulators that can sense nutrient levels and/or cellular energy status resulting in an anabolic or catabolic phenotype according to nutrient availability. Furthermore, we hypothesize that several of these pathways operate both independently from and coordinately with the hormonal pathways. It is through these mechanisms that the tissue responds to glucose, amino acids, and fatty acids, or the products of their catabolism.

Specific objectives are 1) To determine global gene expression patterns in mammary tissue in response to nutrients both in vivo and in vitro, and 2) To relate mammary gene expression profiles with other physiological measurements such as mammary nutrient uptake from blood, milk composition, and milk component output.

Potential benefits: The U.S. multiple component pricing (MCP) system provides powerful economic incentives for dairy producers to produce milk solids that have high commercial value (fat and protein) while providing no incentive for production of components directly tied to milk volume (lactose and minerals) that have little or no value. It has been speculated for some time that although alteration of milk fat and milk protein composition could be achieved, they are unlikely to be an important component of genetic improvement in dairy cattle (Gibson, 1989). Therefore, producer responses to short term market fluctuations such as those that have recently occurred in the U.S. will require rapid and targeted approaches. In these instances, the ability to rapidly alter milk fat or milk protein concentrations would be highly advantageous. Research into targeted feeding practices that make use of feed supplements including oil seeds, vegetable and fish oils, and rumen-protected amino acids (e.g., Lys, Met) have shown the potential to increase the management options available to dairy farmers for the production of milks that differ in their composition.

Results from previous investigations with non-ruminant species suggest that cellular nutrient signaling is a key mechanism by which diet regulates tissue metabolism. Most of those studies have monitored the changes in gene expression that take place in cells or tissues after exposure with a specific nutrient.  Although the basic metabolic aspects underlying milk fat and protein synthesis in the cow were previously examined in classical studies at the University of Illinois (Andersen & Larson, 1970; Mellenberger et al., 1973; Collier et al., 1977), there is a great paucity of information on nutrient-gene interactions in key metabolic tissues. Transcriptional profiling coupled with metabolic end points in blood and milk should provide a wealth of information on as yet unknown molecular adaptations in response to nutrition and physiological state.