SYSTEMS BIOLOGY OF REGULATORY MECHANISMS OF NUTRIENT METABOLISM IN LACTATION
The role of the dairy cow is to help provide high-quality protein and other nutrients for humans. We must select and manage cows with the goal of reaching the greatest possible efficiency for any given environment. We have increased efficiency tremendously over the years, yet the variation in productive and reproductive efficiency among animals is still quite large. In part this is because of a lack of full integration of genetic, nutritional, and reproductive biology both in research and management decisions. However, integration across these disciplines is increasing as biological research findings show more specific control points at which genetics, nutrition, and reproduction interact. An ordered systems biology approach that focuses on why and how cells regulate nutrient use and on how and why organs interact by endocrine and neurocrine mechanisms will speed improvements in efficiency. Nutrient metabolism is controlled by a number of factors including type and amount of intake, stage of lactation, and amount of milk production; through a complex system of neurocrine and endocrine regulation. In turn, nutrient metabolism in the brain, liver, splanchnic organs and muscle directly affect the efficiency of the animal. The metabolic efficiency of the mammary gland runs at its thermodynamic maximum unless there is a physiological disease or a massively imbalanced ration. The variation in efficiency of animals is a result of variations in metabolism in non-mammary tissues; including nutrient metabolism in the liver, protein turnover in the muscle, and lipid turnover in the adipose tissue. These metabolic paths are allotted to maintenance costs in practical application. Thus, using a systems biology modeling approach, we can design experiments specifically to integrate our knowledge on tissue metabolism, food intake, milk production and overall efficiency. Data from genomic studies, transcriptional arrays, endocrine and neural signals, tissue metabolism and animal level experiments can be integrated to clearly indicate which are the controlling factors. This approach can help focus our research to make faster and large advances in efficiency and show directly how this can be applied on the farms.
Keywords: systems biology, lactation, metabolism