Like cattle, whitetails are ruminants, or cud chewers. They gulp food without chewing and store it in the rumen, the first and largest chamber of their 4-part stomach. This feeding behavior is advantageous in severe weather or when hunting pressure is heavy. The deer can feed rapidly when the opportunity presents itself, easily consuming 5 pounds of food in a half-hour. Then they retreat to the safety of heavy cover.
Once bedded, the deer regurgitates food from its rumen, chews its cud (the term for regurgitated food) and swallows it. The food then passes through the other stomach chambers for further digestion.
The rumination process allows whitetails to digest a wide variety of plant material. Primarily grazers, deer gain weight quickly during the growing season by consuming grasses, forbs, legumes, agricultural crops (especially corn and soybeans), flowers, nuts, fruits, vegetables, emergent aquatics, mushrooms, winter buds of woody plants and high-moisture succulents such as cactus.
Heat produced by the digestive process affects deer behavior. Hot weather, along with the heat of digestion, reduces their activity; they seek cover in a cool, shady spot. On winter nights, the rumen acts like a furnace. Except in the coldest weather, deer can stay bedded without losing so much heat that they have to get up and move around.
Digestion is very efficient; only about 5 percent of the food cannot be digested and is expelled as hard, relatively dry pellets.
Deer have no upper front teeth. To eat a bud, for instance, they pinch it between their lower front teeth and the “tire tread” roof of their mouth, then pull. Frayed twig ends are a sure sign of deer feeding activity.
Bucks feed heavily and build up fat reserves in spring and summer. But during the breeding season, adult bucks eat very little and use up fat as they pursue does and spar with other bucks. Although does consume large quantities of food in summer, they lose weight while nursing their fawns. They regain weight rapidly in fall in preparation for pregnancy.
Whitetails may have a tough time finding nourishing food in winter. Snow covers high-quality foods such as acorns and crop residue, forcing deer to eat browse. Their activity and metabolism slow down, and they typically lose 20 percent of their weight as they use up fat reserves. Severe cold and deep snow aggravate the problem even more because they increase the energy drain.
The stomach consists of four chambers. The largest is the rumen, which stores food until it is regurgitated and rechewed. Reswallowed food ferments in the rumen and the second chamber, the reticulum. Then it passes to the omasum and abomasum, which absorb water and minerals and break down proteins.
Severe droughts and floods can also cause food shortages. Conservation agencies monitor the condition of deer herds, and if these conditions persist too long, may call upon sportsmen’s groups to cooperate in distributing high-quality deer foods such as alfalfa pellets. Although feeding programs are expensive and deer in remote habitats, such as northern forests, are difficult to reach, they can be saved if feeding starts early enough. In a severe winter, however, deer may not have time to develop the rumen bacteria that will digest the new food, so they could starve to death with a full stomach. Any deer that loses more than 40 percent of its body weight will not recover.
How much water deer require depends on the climate, time of year, their activity level and the moisture content of their food. Given a choice, deer eat the food with the highest moisture level. In wet climates, deer get practically all of their water from their food. In dry climates, they require additional water and may visit water holes several times a day. In winter, they get additional water by eating snow.