Influence of Gut Metabolism on Nutrient Supply in Ruminants: Introduction

Abstract

Much is known about gut metabolism and gut in volvement in nutrient absorption. Yet a more complete understanding of the mechanisms involved in nutrient transport, of the numerous factors regulating and/or influencing nutrient transport and of the extensive met abolic activity of gut tissues is needed. This symposium reviews three areas of gut nutrient transport and meta bolic activity that have been undergoing considerable research in recent years. lonophores are commonly used feed additives in the production of both ruminants and poultry. It is well established that ionophores influence rumen microbial metabolism, with the primary result being a relatively greater proportion of propionate and a relatively lesser proportion of acetate being formed in the rumen from carbohydrate fermentation. The anticoccidial proper ties of ionophores contribute to their wide use in poultry production. Becausevarious cations may be selectively bound by ionophores, because these cations may be important nutrients to be absorbed and because these cations may play critical roles in nutrient transport, we must consider the potential influence ionophores may have on nutrient absorption. The involvement of iono phores in nutrient digestion and absorption is discussed by Spears (1). In ruminants, much information is available describ ing the influence of dietary change on the production of end products of microbial fermentation, primarily in the reticulorumen but also in the large intestine. Even though absorption and metabolism of volatile fatty acids by tissues of the reticulorumen have been studied for many years, it is not completely understood how these tissues may influence the availability of nutrients to peripheral tissues. Also, factors that affect the devel opment and expression of nutrient uptake by the enterocytes are of interest. Information is emerging regarding the interaction of the microbial flora of the gut and nutrient absorption. Parker (2)presents a discussion of how the absorptive activity of the gut may be influ enced by dietary factors and by the control of microbial flora through the use of antibiotics and probiotics. Even small changes in the efficiency with which energy is used by animals can have profound effects on animal productivity. Recently, researchers have learned that visceral tissues, especially the gastrointestinal tract and liver, have a disproportionately high rate of energy use compared to most other tissues. Understanding the factors that influence energy use by these visceral tis sues may enable us to control these processes and thus control the efficiency of animal production. A discus sion of changes in liver and gastrointestinal tract energy demands in response to physiological workload is pre sented by Johnson et al. (3).