A manager should consider deer nutrition on a seasonal basis. Changes in the nutritional requirements of deer that occur with gestation, lactation, breeding and antler growth should be coordinated with seasonal changes in nutrient availability from forage plants. Nutritional requirements of deer are generally separated into five categories: protein, energy, minerals, vitamins and water. Research on deer nutrition has primarily focused on protein, energy and minerals (phosphorus and calcium). These requirements are most often the ones that limit growth, reproduction and antler development.
Protein is very important for body growth in deer, especially for fawns and yearlings. Inadequate protein intake in a given year will also reduce antler development. In fact, a period of inadequate nutrition (low protein) for buck fawns may adversely influence antler development for several succeeding years. A deer must obtain at least a 6 to 7 percent crude protein diet to maintain rumen function, but a protein diet in the 13 to 16 percent range is required for successful growth, antler development and reproduction.
EnergyEnergy requirements of deer are not well-known, particularly how energy demand may be affected by weather conditions and the physiological state of deer. Energy deficiencies can result in cessation of growth, weight loss, reproductive failure and impaired rumen function. Most research in Texas done on deer forage quality has primarily focused on protein and mineral levels of food plants, not on energy content. However, several recent studies have included a qualitative measurement called dry matter digestibility (DMD), a measure closely related to digestible energy. Although DMD will slightly overestimate the energy content, DMD is a good indicator of digestible energy for most plants. A summary of available research data indicates that adult deer require forages with DMD of 50 to 55 percent, which increases to approximately 65 percent for lactating does. As forage plants mature and their quality (including energy) declines in July and August, does experience the stress of lactation and bucks require greater nutrient levels for antler production. Therefore, energy may be limiting during late summer, particularly during the drought years,
Most research on mineral requirements of deer has involved growing fawns. Little information is available on requirements of adult deer, particularly for maximum antler growth in bucks. A phosphorus intake level of approximately 0.35 percent is necessary to provide maximum weight gain, bone growth and antler development in yearling bucks. With the exception of a few plants in early spring, few forage species contain this level of phosphorus. Therefore, phosphorus may be a limiting nutrient in South Texas for a maximum antler growth. Diets containing 0.40 percent calcium and 0.28-0.30 percent phosphorus are required for acceptable growth and development in deer. Sodium, potassium, chlorine, zinc, iron, magnesium and other minerals are important, but most are needed in very small amounts and are usually supplied in common forage plants.
Very little research has been conducted on vitamin requirements of deer. Vitamins A, D and E are among the more important vitamins for proper growth and development in deer. Vitamin A is undoubtedly important for antler growth as hardening (ossification) occurs. Deer can convert carotene in green leaves into vitamin A, which then becomes available for a variety of functions. During most of the year, carotene intake should be more than adequate, but slight vitamin-A deficiencies may occur during harsh, dry winters. Vitamin-D is probably important in promoting calcium absorption and the mineralization of bone as it is in other species. Vitamin-D requirements are probably met by exposure to sunlight (ultraviolet light) and by the consumption of ultraviolet irradiated plant tissues. Vitamin-E is important for preventing muscle tissue damage in deer that are subjected to severe physical exertion.
Water requirements for deer vary with climate, type of food, physiological state and amount of activity. The amount of free water consumed is inversely proportional to the concentration of water in food. Although it has not been experimentally established, deer can probably survive without free water if green forage is abundant. Forage plants often contain significant amounts of water (45 to 65 percent in browse and 70 to 90 percent in forbs). Pricklypear is especially important as a source of water (90 percent) for deer in South Texas. Free water may be important in South Texas than more temperate regions, especially during the hot, dry summers with temperatures commonly rise above 100 degrees F. Water availability can be critical during drought situations when forbs and other succulent vegetation are scarce. Ranchers may improve deer performance by locating a water source every 1000 acres or less during droughts or dry seasons.