Deer do consume grass, but these plants generally form a small part of their overall diet. Deer are highly adaptable herbivores, which allows them to thrive across diverse habitats. Their feeding behavior is opportunistic, meaning they will eat whatever is available to provide necessary nutrition, even if it is not their first choice. This flexibility allows them to switch between food sources as availability changes throughout the year.
Deer as Ruminant Animals
The ability of a deer to process fibrous vegetation, including grass, is rooted in its anatomy as a ruminant animal. Like cattle and sheep, deer possess a specialized digestive system centered around a four-compartment stomach. The largest compartment is the rumen, a fermentation vat where symbiotic microbes break down complex plant cellulose.
The partially digested material moves to the reticulum, which sorts the material and forms the cud. Deer periodically regurgitate this cud for extensive re-chewing, a process called rumination. This mechanical breakdown significantly increases the efficiency of nutrient extraction from indigestible matter.
The material then passes through the omasum, which absorbs large amounts of water and minerals. Finally, it reaches the abomasum, which functions as the true stomach. Here, standard digestive acids and enzymes break down proteins and remaining nutrients before absorption in the intestines. This specialized pathway makes consuming tough, fibrous material like grass possible.
Browsers Not Grazers
Although their digestive system permits grass consumption, deer are biologically classified as concentrate selectors, or browsers, rather than grazers. Grazers, such as bison or cows, have digestive systems optimized for handling large volumes of low-quality, high-fiber grasses. Browsers, conversely, seek out easily digestible, high-nutrient foods, selecting for quality over quantity.
A deer’s primary diet consists of browse, including the tender shoots, leaves, and twigs of woody plants, along with forbs. Forbs are broad-leafed herbaceous plants like clover and dandelions, which are significantly higher in protein and lower in indigestible fiber than grass. Deer meticulously select the most palatable and nutrient-dense parts of a plant rather than consuming large swaths of vegetation indiscriminately.
Deer have a relatively smaller rumen size and faster digestive throughput compared to true grazers. This means they cannot efficiently process the large quantities of low-quality forage required to sustain themselves on a grass-only diet. Grass is typically relegated to a secondary food source, consumed when preferred, high-quality browse is sparse. Their digestive metabolism is better suited for the concentrated energy found in leaves and soft stems.
Seasonal Changes to the Menu
The proportion of grass in a deer’s diet shifts based on the seasonal availability. During the growing seasons of spring and summer, the diet is dominated by high-quality forbs and woody browse. These months offer maximum nutritional return, allowing deer to build fat reserves and support reproduction.
When winter arrives and herbaceous plants die back, deer rely on lower-quality, dormant food sources. Their diet constricts, consisting mainly of the dried stems and buds of woody vegetation. Grass consumption, including dried grasses or hay, may increase during this period of scarcity because it is one of the few available forms.
Grass consumption also sees a temporary spike in early spring, as the first new shoots emerge before other preferred plants have fully leafed out. However, once tender leaves and high-protein forbs become widely available, deer rapidly shift away from grass to maximize their intake of calorie-dense sustenance.