Seasonal nutrient content in food plants of white-tailed deer on the South Texas Plains.

From September 1976, through August 1978, 34 white-tailed deer food plants were collected during the months they were eaten by deer on the H.B. Zachry Randado Ranch in south Texas and analyzed for crude protein (CP), P, Ca, K, Mg, and Na. In vitro dry matter digestibility (DMD) was measured on foods collected only during the first year of the study. Mean levels of CP, Ca, K, and Mg were adequate for deer throughout the year. The P levels were generally inadequate except during spring, whereas Na levels probably were deficient throughout the year. However, these may not be as deficient as indicated because deer select higher quality plants and plant parts. Crude protein content of browse species was generally higher than that of forbs and cacti. Forbs were generally higher in P and Na than were browse and cacti. Although pricklypear cactus generally had low levels of CP, P, and Na, it had a higher DMD (276%) than all other species. However, because of its high soluble ash content (2Oq/), pricklypear cactus averaged about 56% in vitro digestible organic matter. Our data indicated that range managers should provide a diversity of plant species to provide an optimum habitat for deer. Intensive management of deer requires a thorough understanding of the benefit they derive from each range forage species. Many studies have been conducted on the food habits of white-tailed deer (Odocoileus virginianus) in south Texas (Davis 195 1; Davis 1952; Davis and Winkler 1968; Chamrad and Box 1968; Drawe 1968; Everitt and Drawe 1974; Arnold and Drawe 1979). However, deer nutrition was included in only the more recent studies (Varner et al. 1977; Everitt and Gonzalez 1979; Kie et al. 1980). Thus, a more thorough understanding of the nutritive value of important deer foods in south Texas would enhance deer management. Our objective was to measure the seasonal nutritive value of preferred white-tailed deer foods on the H.B. Zachry Randado Ranch (Zachry Ranch) in the western South Texas Plains. Thirtyfour preferred foods were collected during the seasons they were eaten by deer. The foods were selected for study on the basis of studies on white-tailed deer food habits conducted on the Zachry Ranch by Everitt and Drawe (1974), Arnold (1976), and Arnold and Drawe (1979). Study Area and Methods The Zachry Ranch is about 44 km southwest of Hebbronville Authors are range scientists, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Weslaco, Texas 78596. This study is a contribution from U.S. Dep. Agr. , Sci. and Educ. Admin., Agr. Res., Soil and Water Conserv. , Res., Weslaco, Texas. The authors wish to thank personnel of the H.B. Zachry Ranch for their help and cooperation in this study. Special thanks is extended to Dr. Mort Kothmann, Department of Range Science, Texas A&M University, for determining the in vitro digestible organic matter of pricklypear cactus samples. The authors also acknowledge the help of M.A. Alaniz and G.V. Latigo. Weslaco, Texas, for their assistance in chemical analyses. Manuscript received. 506 and 40 km northeast of Zapata in Jim Hogg and Zapata Counties. It is in the South Texas Plains vegetational region (Gould 1975). The ranch has 3,045 ha of rolling brushland intersected by caliche hills and gulleys. Eight soil types and six range sites lie within the ranch, but most of the ranch is a sandy loam site comprised of McAllen (Aridic Ustochrepts) and Brennan (Aridic HaplustalfsY fine sandy loam soil types (Higginbotham 1975). The area’s climate is mild with short winters and relatively warm temperatures throughout the year. The average length of the growing season 300 days (USDC 1970). Average annual rainfall is 52 cm and usually occurs in association with thunderstorms that are unevenly distributed both geographically and seasonally. Occasionally, tropical disturbances produce heavy rainfall, thus September has the highest long term monthly rainfall average with another rainfall peak in May or June from squall-line thunderstorms. The rainfall is lowest in January or February. The 34 preferred white-tailed deer plant foods studied are listed in Table 1. Samples were collected mid-monthly from September 1976 until August 1978. Each plant species was collected during the months that it is usually eaten by deer on the Zachry Ranch. Several plants were collected every month because they were eaten throughout the year. The months were grouped by seasons as follows: spring (March-May); summer (June-August); fall (September-November); winter (December-February). Plant samples were randomly hand-clipped primarily from the sandy loam site, since the major plants were found on this site and because this site comprised most of the ranch. However, samples of the most eaten plant species also were collected from some of the minor range sites and pooled with those from the sandy loam site for chemical analyses. Only leaves and the ends of twigs were clipped from browse plants but both whole plants and leaves were collected from forb species because deer consumed various parts of these plants. Composite samples of 12 or more plants were washed with distilled water, air dried at 65” C, ground in a Wiley mill through a l-mm mesh screen, thoroughly mixed, and stored in sealed jars. Plant samples were analyzed for crude protein (CP), P, Ca, Mg, K, and Na. Total N was determined by the Kjeldahl method (Peech et al. 1947). Nitrogen levels were multiplied by 6.25 and expressed as percent CP. Levels of Ca, Mg, K, and Na were determined by atomic absorption spectrometry (Boettner and Grunder 1968). Lanthanum oxide was added to Ca and Mg samples to reduce interference. Phosphorus was determined by the rapid digestion method (Bolin and Stramberg 1944). Plant samples were analyzed in duplicate, and duplicate results were averaged. In vitro dry matter digestibility (DMD) was determined by the two-stage technique of Tilley and Terry (1963). Within a week after collection, duplicate samples of each plant species were treated with rumen inocula obtained from doe deer, killed on the Zachry Ranch. Rumen contents were placed in a prewarmed insulated container and taken to the USDA laboratory at Weslaco, Texas, within 2 hours after deer were killed. The DMD percentages were JOURNAL OF RANGE MANAGEMENT 34(6), November 1981 Table 1. Crude protein, phosphorus (P), and dry matter digestibility (DMD) of spring and summer foods of white-tailed deer on the Zachry Ranch in south Texas.