Explain that this is what happens to feed in the digestive process. Millions of bacteria and protozoa grow in the mass of water and feed in the rumen. They reproduce and grow using the digested material, primarily the protein. This is a way of life in which two organisms of different species live in intimate association with each other. This begins in the stomach with pepsin, an enzyme found in the gastric juices.
Final digestion is in the small intesting where absorption also occurs.
Fats do not undergo digestion until they reach the small intestine. Put some barley into a beaker and add sulfuric acid to it. Ask the students what is happening. Explain that this is what happens to a feed being digested in the animal's stomach. The blood, containing these nutrients, reaches the capillaries in all the body tissues.