Net nutrient flux across the portal-drained viscera and liver of ruminants

Abstract

Tissues of the portal-drained viscera (PDV; reticulo-rumen, omasum, abomasum, small and large intestines, cecum, pancreas, spleen, and omental fat) and the liver are key to the digestion, absorption, transport, metabolism, and recycling of nutrients required for the maintenance, growth and lactation of ruminant animals. Changes in blood flow, oxygen consumption and net nutrient flux across the portal-drained viscera and liver ultimately drives animal production. The PDV is the intermediary between dietary feedstuffs and the profile of nutrients available for maintenance or production. The liver metabolizes components of portal blood as well as arterial blood and serves as a center or “hub” of intermediary metabolism for the entire animal. Splanchnic tissues (PDV and liver) use 40-60?% of the oxygen consumed by the whole body of ruminants. The large partitioning of energy expenditure stems from the important activities that splanchnic tissues contribute to homeostasis, as the removal or release of nutrients and hormones by splanchnic tissues regulates substrates provided to the animal for maintenance, growth and/or lactation. Previous research has demonstrated that differences in age, body weight, diet, and level of intake affect metabolism by the PDV and liver. Understanding rumen function and net portal-drained visceral and liver flux of nutrients is important, because dynamics of the splanchnic tissues are ultimately responsible for providing nutrients to the host animal. This chapter will summarize the literature regarding net nutrient exchange across the PDV and liver relative to specific production scenarios of ruminant animals.