Actually, no animal has a specific requirement for carbohydrates. The soluble carbohydrates (starches and sugars), are the major source of energy for nearly all herbivores (plant-eating animals) and omnivorous (plant and meat eaters), such as we humans. Since the deer is a ruminant (a cud-chewer with a four-chambered stomach), like a cow or sheep, it can digest fiber, better known as cellulose. Since deer are primarily browsing animals, their diets contain forbs, brush (leaves, twig ends, buds, bark), some hard and soft fruits, and a small amount of grass. In short, they eat little starch, but a lot of fiber.
Fiber is useful to deer not only for energy, but also for keeping the rumen healthy. Just like dairy cattle, deer need a fibrous diet, and could not exist for long solely on a concentrated ration. This is important when we consider supplementing deer. A deer consuming a pile of corn could go into toxic acidosis, just like any other ruminant. Supplemental feeds, if used at all, should be food plots, or pelletized, mixed-grain, high-fiber rations.
Lipids are quite simply defined as fats, if they are solid at room temperature, or oils, if they are liquid at room temperature. Deer have no specific requirements for lipids, but the fats and oils in their diets do provide an important source of energy. In fact, lipids have 2.5 times the amount of energy per gram as do proteins or carbohydrates. Thus, the oils in foods like acorns are important as an energy source. Deer milk is 7.7 percent fat, nearly double that of cows milk.
Deer build layers of fat during the summer and fall to prepare for winter. But they do not need fat in the diet to do that. They convert the energy in carbohydrates to saturated adipose fat, then use that fat during hard times. This is a natural phenomenon, and one of the reasons the nutrient requirements and food intake of deer in the winter is so low. Adipose, or depot fat, is readily available to burn for energy when needed, and fat in the muscle, known as marbling, is very low in deer.