In ruminant animals, absorption of nutrients occurs primarily in the small intestine, where the small molecules resulting from the breakdown of food in the rumen and reticulum are further broken down and absorbed into the bloodstream.
The small intestine of ruminants is relatively short compared to non-ruminants, but it has a large surface area due to the presence of villi and microvilli, which are finger-like projections that increase the absorptive surface area. In addition to these structures, the small intestine of ruminants also contains numerous crypts, which are small invaginations in the epithelial lining that produce digestive enzymes and mucus.
The small intestine is divided into three regions in ruminants: the duodenum, the jejunum, and the ileum. The duodenum receives bile and pancreatic juice from the liver and pancreas, respectively, which contain digestive enzymes that help to further break down proteins, fats, and carbohydrates. The jejunum and ileum are primarily responsible for the absorption of nutrients.
As the small molecules from the rumen and reticulum pass through the small intestine, they are absorbed into the bloodstream through the walls of the villi and transported to the liver via the portal vein. The liver plays an important role in the metabolism of nutrients, including the synthesis and breakdown of carbohydrates, fats, and proteins. The liver also helps to regulate the concentration of nutrients in the bloodstream, such as glucose and amino acids.
In addition to the absorption of nutrients in the small intestine, ruminants also absorb some nutrients in the large intestine, specifically the cecum and colon. These regions of the digestive tract contain bacteria that can synthesize certain vitamins, such as vitamin K, and break down cellulose and other plant fibers, releasing additional nutrients for absorption.
Overall, the process of nutrient absorption in ruminants is a complex and highly coordinated process involving multiple organs and structures. The unique digestive system of ruminants, including the fermentation chamber in the rumen and reticulum, allows them to efficiently break down and absorb nutrients from plant-based diets.