Ruminant Physiology and Function

Knowledge Nuggets

• The digestive tract is composed of the mouth, tongue, teeth, esophagus, stomach, small and large intestines. A ruminant stomach is comprised of four compartments the rumen, reticulum, omasum and abomasum.

• The mouth is the location where food enters the system and is chewed. Salivary glands are found in the mouth that secrete saliva which has a pH of about 8.2. Saliva helps to reduce acidity in the rumen and also aids in the transfer of food from the mouth to the rumen via the esophagus.

• The rumen and reticulum are often discussed together since each compartment is separated by a low partition within the stomach. Eighty percent of the capacity of the stomach is related to the reticulo-rumen and is located on the left side of the animal.

• The rumen is the main fermentation vat where billions of bacteria, protozoa and fungi attack and break down feed. In the breakdown, they produce Volatile Fatty Acids. The ruminant receives nutrients from a number of sources, including energy from VFA's, and the microbes that have been washed out of the rumen and digested in the small intestine.

• A large portion of the cow's protein needs is supplied by these microbes. It is important to remember to feed the animal and the microbial population in the rumen.

• After fermentation in the reticulum and rumen, the feed passes to the omasum which acts as a filter pump to sort liquid and fine food particles. Also, the omasum is the site for absorption of water, minerals and nitrogen.

• The abomasum is the true stomach and the only site on the digestive tract that produces gastric juices. In the newborn calf, the abomasum makes up about 80 percent of the total stomach volume, while in the mature cow it amounts to only 10 percent. Feed only remains here for 1 to 2 hours.

• The small intestine is the location where a further breakdown of the food material occurs. Secretion of enzymes, pancreatic juice and bile, aid in further digestion of the feed occurring in the upper portions of the intestine. The end products of the digestion process are absorbed in the lower section of the small intestine.

• The large intestine is where residues of the ingested feed are deposited, further fermented and absorbed.

• Residue that exits the large intestine enter the colon and is excreted as manure.