Sheep Digestive Physiology and Constituents of Feeds

Abstract

Sheep have a gastrointestinal tract similar to that of other ruminants. Their stomach is made up of four digestive organs: the rumen, the reticulum, the omasum and the abomasum. The rumen plays a role in storing ingested foods, which are fermented by a complex anaerobic rumen microbiota population with different types of interactions, positive or negative, that can occur between their microbial populations. Sheep feeding is largely based on the use of natural or cultivated fodder, which is exploited in green by grazing during the growth period of the grass and in the form of fodder preserved during the winter period. Ruminant foods are essentially of plant origin, and their constituents belong to two types of structures: intracellular constituents and cell wall components. Cellular carbohydrates play a role of metabolites or energy reserves; soluble carbohydrates account for less than 10% dry matter (DM) of foods. The plant cell wall is multi-layered and consists of primary wall and secondary wall. Fundamentally, the walls are deposited at an early stage of growth. A central blade forms the common boundary layer between two adjacent cells and occupies the location of the cell plate. Most of the plant cell walls consist of polysaccharides (cellulose, hemicellulose and pectic substances) and lignin, these constituents being highly polymerized, as well as proteins and tannins.