Nutritional systems biology to elucidate adaptations in lactation physiology of dairy cows

A fuller understanding of the complexity of physiologic and metabolic adaptations experienced by the modern high-producing dairy cow during the transition into lactation unavoidably requires application of systems biology, i.e. a way to systematically study the biological interactions within the cow using a method of integration instead of reduction. The use of high-throughput technologies, i.e. "omics," along with bioinformatics are ideal for uncovering pathways, regulatory networks, and structural organization within and between tissues (e.g. adipose and liver, skeletal muscle and adipose, gut microorganisms and epithelia). The integration of this information results in a more holistic appreciation of how the cow functions, particularly when used within a framework encompassing nutrition as a tool for optimizing the ability to adapt to lactation without compromising health. This chapter fi rst outlines the current state of biological knowledge on fi ve key areas identifi ed as crucial for achieving marked gains in productivity. After a brief description of high-throughput technologies, we discuss breakthroughs in knowledge at the tissue, cell, and rumen level. Major topics include regulation of feed intake, immune function, fat deposition, and the rumen microbiota. The goal is to provide specifi c examples of how genome- enabled approaches have been used to advance our understanding of tissue and cell function, and microbiota adaptations to dietary changes during the transition into lactation. The available research illustrates how a more widespread application of systems biology in ruminant nutrition will, in the medium-to-long-term, enable scientists to design functional diets that enhance dairy cow productivity and health based on exploiting the plasticity of the rumen microbial ecosystem along with the cow’s full genetic potential.