Rumen Function and Microbiology

Shane Horrocks M.S.
Wildlife Nutritionist
MaxRax Wildlife Nutrition

Whitetail Deer, like other ruminant animals, have a stomach with four compartments:  the rumen, reticulum, omasum and abomasum.  The rumen is the largest compartment with a volume of approximately 1.85 gallons in a 225lb deer, and it maintains a pH between a 6 and 7.2 depending on feed, age and season. It serves as a storage site for ingested feed that is later regurgitated and re-chewed and as a fermentation vat for the production of volatile fatty acids (primary energy source in ruminants). The micro environment is capable of producing proteins and vitamins (B, and K) and it houses a large, diverse microbial population (beneficial bacteria, protozoa and fungi). The rumen is comprised of a muscle layer that contracts and relaxes to assist the mixing of ingested feed, which allows microorganisms to attach to and utilize swallowed feed particles. The muscle layer also assists with regurgitation of feed for further mastication and passage of feed material out of the rumen and eventually into the intestines. The inner wall of the rumen is made up of specialized epithelial tissue responsible for absorbing volatile fatty acids produced in the rumen and nitrogen from plants. Volatile fatty acids are eventually used as energy and the nitrogen is eventually recycled to the rumen via the saliva to be assimilated into more rumen microorganisms and protein for the deer to use. Consistency of rumen function is critical to overall animal health.  Indicators like pH level, microbial density, and nutrient quality and quantity must be optimal to achieve desired animal performance.
Factors like diet, stress level, and a healthy rumen microbial population contribute to the efficiency of the rumen and its ability to produce nutrients for the deer. Microorganisms are needed to produce energy, proteins and vitamins essential for proper tissue growth, reproduction, and lactation. When a deer consumes hay or grain, the beneficial microorganisms in the rumen will ferment the fibrous (cellulose and hemicellulose) portions of the grain and produce energy products called volatile fatty acids. Volatile fatty acids are made into sugars, like glucose, which are then used to sustain the deer’s energy needs. Microorganisms can also utilize non protein nitrogen from the grains or hay to reproduce and make microbial proteins, which are critical components of rumen microorganisms. Microorganisms that are passed out of the rumen and into the deer’s intestine are digested and the protein from the cells are absorbed just like protein from soybeans or alfalfa. The deer can then use the microbial protein to meet some of their daily protein requirements. For this reason, ruminant feeds are specifically developed and balanced to maintain optimal amounts of protein, non protein nitrogen, and carbohydrates that can be used for efficient production and turnover of rumen microorganisms.
High quality, well balanced feeds can improve rumen health by promoting a diverse microbial population capable of utilizing carbohydrates, proteins, and fatty acids, and can decrease potential rumen problems. For example, as carbohydrates (fibrous and non-fibrous) and proteins are utilized by the microorganisms in the rumen, gases, such as carbon dioxide and methane, will be produced. A healthy functioning rumen is capable of expelling these gases; However, unbalanced diets, like high grain or high legume diets, or the use of drugs can impact the rumen’s ability to function correctly and inhibit the deer’s ability to release the gases. Grain overload in ruminant diets can alter the rumen microbial population many ways. Some grains utilized by rumen microorganisms will produce lactic acid. If a ruminant consumes too much of a particular grain, like corn, a high amount of lactic acid will be produced causing a drop in rumen pH. An acidic rumen environment can kill microorganisms, like fiber degrading organisms, because they are unable to survive under highly acidic conditions.  Consequently, cell death can create an imbalance in the microbial population and lead to lactic acidosis. Acidosis can destroy the epithelial tissue responsible for absorbing nutrients through the rumen wall and into the blood stream. Other problems that can occur with an unbalanced microbial population are bloat (acute or chronic) and reduction or elimination of B vitamin synthesis (which can cause blindness) within the rumen. These potential health threats can all be avoided by feeding a sound and balanced daily feed. A good quality feed has safe concentrations of soluble carbohydrates (starch), adequate levels of fiber, and is well balanced to provide accurate levels of ingredients to not only the animal consuming it, but also the microbial population living in the rumen.