Yes, deer chew their cud. This behavior is a fundamental part of their digestive process, classifying them as ruminants, a group of mammals that includes cattle, sheep, and goats. Cud chewing allows deer to efficiently process the fibrous plant material that makes up the majority of their diet. This adaptation enables them to extract maximum nutrition from tough vegetation, which is initially swallowed quickly and later re-chewed at leisure.
Understanding the Ruminant Digestive System
Deer possess a unique four-chambered stomach, distinct from the single-chambered stomach found in many other mammals. The first two chambers, the rumen and the reticulum, act as a large fermentation vat where ingested plant material is initially stored and mixed. The rumen is the largest compartment and houses billions of microorganisms, including bacteria, protozoa, and fungi. These microbes begin breaking down complex carbohydrates like cellulose and hemicellulose found in plant cell walls. The reticulum helps sort food particles and traps larger, undigested material.
From the reticulorumen, partially digested food moves to the omasum, the third chamber, which absorbs water and some volatile fatty acids. The omasum also filters particles, ensuring only finely processed material moves forward. Finally, the food enters the abomasum, the “true stomach,” which functions similarly to a monogastric stomach in humans. Here, digestive enzymes and acids further break down the food and the microbes themselves, preparing nutrients for absorption in the small intestine. This multi-chambered system allows deer to initially consume large quantities of forage quickly, then retreat to a safe location for thorough digestion.
The Mechanism of Cud Chewing
Cud chewing, also known as rumination, is a precise and repetitive process that begins after deer have consumed forage. When at rest, a portion of the partially digested food, or cud, is regurgitated from the reticulorumen back into the mouth. This regurgitation is initiated by a contraction of the rumen and a reverse peristaltic wave in the esophagus. The cud, which can be about the size of a large lemon, is then thoroughly re-chewed.
During this re-chewing, deer employ a side-to-side grinding motion using their molars, which effectively breaks down the plant material into much smaller particles. This mechanical breakdown increases the surface area of the food, making it more accessible to microbial action in the rumen. Concurrently, large amounts of saliva are mixed with the cud, aiding in lubrication and providing a buffering agent to maintain the optimal pH within the rumen. After extensive re-chewing, the now finer particles are re-swallowed, bypassing much of the rumen and moving more directly to the omasum and abomasum for further digestion.
Importance of Cud Chewing for Deer Health
Cud chewing enables deer to maximize nutrient extraction from their diet, particularly from fibrous plant matter. This process significantly breaks down tough components like cellulose and hemicellulose that mammals cannot digest on their own. The repeated chewing increases the efficiency of microbial fermentation in the rumen, making energy and essential nutrients, such as volatile fatty acids, available to the deer. Without this extensive physical and microbial processing, a significant portion of the consumed forage’s nutritional value would remain inaccessible.
Cud chewing also plays a role in detoxifying certain plant compounds by exposing them to rumen microbes for longer periods. The copious saliva produced during rumination helps buffer the acids generated by fermentation, maintaining a stable and healthy environment for the microbial population in the rumen. This ensures optimal digestive efficiency and contributes to the deer’s overall health and well-being, especially when food sources are of lower quality or highly fibrous. Deer can spend several hours a day ruminating.