Nutritive Content of Sheep, Goat, and White- tailed Deer Diets on Rangeland in Texas Excellent Condition

A one-year study was initiated in August, 1975, to examine the nutritive content in diets of four kinds of sympatric ruminants on excellent condition rangeland of the Edwards Plateau in Texas. Sheep, Angora goat, and Spanish goat diets were collected from animals fitted with permanent esophageal cannulae. Nutritive content of white-tailed deer diets was estimated by hand-plucking representative forages as the deer were observed grazing them. Mean, annual levels of crude protein (CP) were similar among the four kinds of animals. All diets were lowest in CP during January and February, with livestock diets showing higher levels than deer. However, deer diets were higher in CP than sheep and goat diets during spring and summer. During January and February, the livestock diets warranted only minimum protein supplementation while deer diets were significantly below recommended levels. Digestible energy (DE) levels were higher for sheep diets than for diets of either goats or deer. Similarly, the goat diets were higher in DE than deer diets. The DE levels were generally adequate for sheep but critically low for Angora goats during late gestation. Deer diets were very low in DE during winter and again in early summer, coinciding with the period of peak lactation. Energy would appear to be more limiting for animal production than protein under the conditions of this research. Several kinds of herbivores are sympatric on the Edwards Plateau of Texas. The smaller herbivores using the rangeland are sheep, Angora goats, Spanish goats, and whitetailed deer (Odocoileus virginianus L.). Sheep and Angora goats were introduced at the turn of the century, while Spanish goats are a more recent introduction. White-tailed deer have long been part of the endemic fauna. Sheep differ from goats in their foraging preference (McMahan 1964). There are indications that Spanish and Angora goats express different forage preferences under certain conditions (C.A. Taylor, pers. comm.); however, these differences apparently were minor on excellent condition rangeland (Bryant et al. 1979). Differences in observed forage preferences and in nutrient requirements of the different kinds of animals suggest that each may require different management to obtain optimum production. Good range management practices have generally been thought to benefit animal production. Thus, as more producers strive to improve their ranges, it is important to determine, seasonally, nutrients that may limit animal production on ranges in higher condition classes. Information Authors are assistant professor, Range and Wildlife Management, Texas Tech University, Lubbock 79409; professor, Department of Range Science, Texas A&M University, College Station 77843; and professor in charge, Texas A&M University Research Station at Sonora 76950. Portions of this research were submitted in partial fulfillment of requirements for the Ph.D. degree in Range Science at Texas A&M University by Bryant. The authors gratefully acknowledge the assistance of Charles A. Taylor and Ed Huston of the Texas Agricultural Experiment Station. This report is TA 14973 from the Texas Agricultural Experiment Station. Manuscript received March 26, 1979. 410 on nutrient levels in diets from excellent condition rangeland was not available for the Edwards Plateau. The objective of this study was to determine the nutritive content of diets selected by sheep, Angora goats, Spanish goats, and white-tailed deer on an excellent condition rangeland. Study Area and Methods The field research was conducted at the Texas A&M University Agricultural Research Station located on the Edwards Plateau near Sonora, Texas. Topography, climate, and vegetation there have been described by Smeins et al. (1976) and Bryant and Kothmann (1979). Briefly the study area occurs at 735 m elevation, has an average rainfall of 65 cm, and a growing season of 235 days. The study area was an 8-ha enclosure located within a 33-ha pasture and was described in detail by Bryant et al. (1979). From 1948 to 1970, the pasture received light continuous grazing (16 ha/animal unit [au]) with a 2:l:l au ratio of cattle, sheep, and Angora goats, respectively. In 1970, it was rootplowed and seeded with both introduced and native grass species. Stocking rate was subsequently increased to 6.5 ha/au and the Merrill grazing system (four pastures, three herds, 12 mo grazing followed by 4 mo rest) was applied. To take advantage of high forage production, the stocking rate was further increased to 5.4 ha/au in 1974 and to 5.2 ha/au in 1977. This pasture was considered to be in excellent range condition and has consistently yielded the greatest production per animal of any pasture on the Sonora Research Station (L.B. Merrill, pers. comm.). Diets of all four kinds of animals were sampled on five consecutive days each month for 1 yr, beginning August 20, 1975. The livestock and deer were fasted overnight before each collection day. Bryant et al. (1979) reported how the animals were handled and the collection regime. Livestock diets were obtained from four each of Angora goats, Spanish goats, and sheep fitted with permanent esophageal cannulae described by Taylor and Bryant (1977). Due to losses, a total of 8 Angora goats, 11 Spanish goats, and 9 sheep were used to collect diet samples throughout the study. Each sampling day, the extrusa samples were collected in screen-bottomed bags, thoroughly handmixed, and a sub-sample was taken and stored at -20” C for chemical analysis. Twenty, wild-trapped white-tailed deer fawns were raised and trained following the guidelines of Reichert (1972). Two adapted to the rigors of transporting and handling and could still be allowed free range of the study area without the confines of a leash (Fig. 1). At project initiation one fawn was 5 mo old while the other was-4 mo. Thus, the deer used were in their most critical nutritional stage of life, weanling to yearling age (4 to 17 months). Samples of species and their plant parts were hand-plucked each collection day to represent those selected by the deer as they were observed grazing the study area. The basic criteria suggested for use of hand-plucking, the selection of plant parts (Halls 1954) and JOURNAL OF RANGE MANAGEMENT 33(6), November 1960 use of lightly grazed areas (Cook 1964), were observed in tixs study. Hand-plucked samples were frozen within 1 hr of collection and stored at -20” C. All diet and hand-plucked samples were freeze-dried (-50” C, 20-100 microns of pressure) and ground in a Wiley mill to pass a l-mm screen. They were composited across individual animals within days and across days within individual animals for each kind of animal within collection periods. Chemical analyses included organic matter (%), organic nitrogen (%), and in vitro digestible organic matter (%). Crude protein (CP) was calculated by multiplying total organic nitrogen X 6.25; digestible energy (DE) was estimated by the procedure described later. All values reported are expressed on an oven-dry, organic matter basis to avoid variability from ash contamination by saliva. Organic matter was determined by ashing duplicate samples in a muffle furnace at 550° C for 5 hr. Nitrogen determination, expressed as crude protein, followed the micro-Kjeldahl procedure (A.O.A.C. 1970). Invitrodigestibleorganicmatterwasdetermined following the procedures of Van Soest (1970). Sheep and goat samples were incubated 48 hr using steer innocula. The handplucked deer samples were incubated for48 hrusinginnocula from one of the deer used during the study and later fitted with a rumen fistula. Following the incubation, samples were killed with mercuric chloride and stored in a refrigerator until they were refluxed in a neutral detergent solution. Digestible energy was calculated from in vitro digestible and neutral detergent extractable organic matter using the formula: