White-Tailed Deer Habitat: Ecology and Management on Rangelands

2. White-Tailed Deer Nutrition

Importance of Nutrition in White-Tailed Deer Management Nutrition is fundamental to deer management because it determines how many deer a given landscape can support and the productivity of the population. Deer populations are far less productive in nutritionally inadequate habitats than in habitats where nutritional needs are met. Poor nutrition results in reduced ovulation and conception rates in females (Teer, Thomas, and Walker 1965; Verme 1969). If adequate nutrients are not available, milk production by females is reduced, resulting in lower fawn survival (DePerno et al. 2000). Antler size of yearling males is affected strongly by environmental and maternal factors that influence nutrition, including mothering ability, milk production, and health (Lukefahr and Jacobsen 1998). White-tailed deer will not reach their genetic potential for body mass or antler size in habitats that provide poor nutrition (Geist 1986). Management strategies that improve quality of available forage result in increased antler size and body mass of mature white-tailed deer (fig. 2.1). In rangelands, natural habitat often will not provide an optimum diet on a year-round basis, but the higher and more seasonally stable the nutrient levels provided by the habitat, the closer to their genetic potential deer grow. Properly managing habitat and allowing males to survive to maturity should be the first priority in whitetailed deer management when the objective is to produce large-antlered males. Digestive Anatomy White-tailed deer are ruminants with a stomach consisting of four compartments: rumen, reticulum, omasum, and aboWhite -Tailed Deer Nutrition 2 K e y C o n c e p t s ▼ Nutrition is one of the main environmental factors governing the degree to which white-tailed deer can express their genetic potential for productivity, including antler and body growth. ▼ Energy is commonly limiting for white-tailed deer productivity on rangelands. ▼ Deer habitat management should focus on providing conditions under which deer can maintain a positive physiological energy balance. • Abundant, nutritious, easily digestible food reduces foraging time and energy expended during digestion. • Food, water, and cover should be in close juxtaposition and well interspersed to minimize energy expended in travel. • Sufficient areas of dense woody canopy should be available for thermal cover. ▼ White-tailed deer select plant species to eat as a result of learning , inherited traits, and the ability to discriminate between foods based on their nutrient content. 46 chapter 2 ▼ masum (fig. 2.2; Robbins 1993) The rumen acts as a fermentation vat where microorganisms begin breaking down plant material. Deer do not possess the enzymes necessary for breaking down the cellulose that forms the cell walls of plants, so the bacteria, fungi, and protozoa in the rumen carry out this process (Russell and Rychlik 2001). White-tailed deer in a study in the Texas Gulf Prairies and Marshes region had only one genus of rumen protozoa (Pearson 1965). Number of protozoa varied seasonally and were lower during winter, whereas bacteria numbers did not vary seasonally. In contrast, white-tailed deer from the Edwards Plateau of Texas had eight species of rumen protozoa (Dehority, Demarais, and Osborn 1999). Degradation of the cellulose in plant cell walls by microorganisms in the rumen breaks plant material into smaller particles and releases nutrients inside the cells, making the nutrients readily available to be absorbed in the digestive tract (Brown 1994a). Some of the nutrients released are absorbed directly by fingerlike projections inside the rumen called papillae. The numerous papillae lining the rumen increase its absorptive surface area. White-tailed deer in South Dakota have lower density of papillae than mule deer, possibly because they consume a more concentrate diet than mule deer do (Zimmerman, Figure 2.1. Good nutrition is needed for white-tailed deer to reach their genetic potential in antler size. Photograph © Timothy E. Fulbright. white-tailed deer nutrition 47 ▼ Jenks, and Leslie 2006). Concentrate feeders utilize highly nutritious plants, such as forbs, and plant parts, such as leaves and tips of nonwoody twigs, and retain them for a relatively short time in the rumen. Papillae are longer and wider in lactating female white-tailed deer than in females that are not lactating , possibly reflecting the greater nutritional needs of lactating females. Contraction of muscles in the rumen and reticulum mixes fresh plant fragments with microorganisms, aids in expelling gases produced during fermentation, and enables deer to regurgitate food particles (Russell and Rychlik 2001). While deer are resting, they ruminate by regurgitating boluses of food from the...