The idea that deer are like grazing livestock, content to spend their days eating vast fields of grass, is a common misunderstanding. While they are ruminants, a deer’s diet is far more nuanced and selective than simple grazing suggests. Their feeding habits are dictated by an evolutionary preference for nutrient density over sheer volume, focused on maximizing the intake of high-quality forage.
Defining Deer as Selective Browsers
Deer, such as the white-tailed deer, are classified as “concentrate selectors” or browsers. This designation sets them apart from “grazers,” which are bulk eaters like cows. Browsers forage on the tender parts of woody plants, shrubs, and trees, unlike grazers who consume large amounts of fibrous material, primarily grass.
Deer anatomy reflects this difference. They possess a narrow snout and an agile tongue, allowing them to carefully pick the most nutritious parts of a plant, such as soft tips or individual leaves. This selective approach means deer favor quality, easily digestible food sources over the quantity of low-quality, high-fiber forage.
The Specific Role of Grass (Graminoids)
While deer are not primarily grazers, they do consume grass and other graminoids under specific circumstances. Grass is generally a secondary food source, becoming more important when preferred forage is limited. Consumption is highest in early spring when new growth is tender, highly digestible, and rich in nutrients.
Mature grass, however, is composed of high levels of cellulose and lignin, which are difficult for a deer’s digestive system to break down efficiently. Grasses are often the least digestible plant class compared to preferred items like forbs and browse. Deer may resort to eating mature perennial grasses during times of scarcity, such as severe winter or drought, but this often leads to nutritional stress due to the low-quality content.
Essential Browse and Forage Components
The majority of a deer’s diet consists of components that offer higher concentrations of protein, energy, and minerals than grass. Primary food sources fall into three categories: browse, forbs, and mast.
Browse refers to the leaves, buds, and tender ends of woody plants and shrubs, serving as a nutritional foundation due to year-round availability. Browse can make up nearly half of a deer’s annual diet.
Forbs, which are non-woody, broad-leaved plants, are highly preferred for their superior nutritional content, being rich in protein and phosphorus. Their availability is seasonal, peaking during favorable growing conditions.
Mast, including hard mast (acorns and nuts) and soft mast (berries and apples), provides a dense pulse of energy, fat, and carbohydrates. This is important for fat storage in the fall and winter, providing necessary building blocks for body maintenance, antler growth, and fawn development.
Digestive System Adaptations
The deer’s preference for high-quality food is rooted in the structure of its four-chambered stomach. As concentrate selectors, deer have a relatively small rumen capacity compared to true grazers like cattle, necessitating a faster passage rate for food.
This smaller “fermentation vat” means the food consumed must be easily fermentable and highly digestible. If a deer consumes large amounts of coarse, fibrous material like mature grass, the rumen is quickly filled with material that cannot be processed efficiently. The low digestibility of mature grass limits the deer’s ability to extract nutrients before the food must pass through the system.
During winter, when only low-quality forage is available, deer can adapt by increasing the overall volume of gut contents. This allows for a longer retention time, which helps maximize the limited nutrient extraction from a poor diet.