Sixty whitbtailed deer ( Odocoileus virginianus ) were used in three experiments to study the nutritional characteristics of large-toothed aspen ( Populus grandidentata ) . Aspen and white cedar ( Thufa occidentalis) browse were ground and pelleted separately orin mLxtures. Aspen pellets were accepted less readily by deer than were cedar pellets, and the presence of as little as 15 percent aspen in a cedaraspen pellet tended to decrease the digestibilities of dry matter, gross energy, cell-wall constituents, and hemicellulose as compared with 100 percent cedar. This amount of aspen also decreased the concentration of volatile fatty acids, increased the acetate:propionate ratio, and reduced the detectable concentration of protozoa to nearly zero in nlmen fluid. Addifion of urea nitrogen (0.9 percent urea 281) to pellets composed of 85 percent cedar and 15 percent aspen increased digestibility of crude protein and the acetate:propionate ratio of the rumen fluid and decreased the concentration of glucose in the blood plasma. The addition of 10 percenkt cornstarch as a supplementary source of energy improved digestibility of dietary dry matter, gross energy, cell-wall constituents, and hemicellulose and increased the concentration of rumen protozoa. A combination of urea and starch produced the greatest improvement in significant nutritional parameters, except for ie concentration of protozoa. Application of these findings to deer management requires the identification of other native food species that could improve the supply of nitrogen and available energy to wintering deer and that are amenable to techniques of forest management. During extreme winter emergencies, appropriately formulated energy-producing and nitrogen supplements may be helpful in improving utilization of cedar-aspen bronvse. Management of the Michiga,n whitetailed deer is ultimately dependent upon adequate browse to support over-wintering. Largotoothed aspen is a fast-growirlg species of interest to the wood pu,lp industry and amenable to forest management. Under certain circumstances, it is intensively browsed by deer, but when it is ffie only ingredient in the diet of penned de,er, aspen 1 Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 5359. Supported in part by the Michigan Department of Natural Resources and Pittman-Robertson Federal Aid in Wildlife Restoration Project Michigan W-95LR-11. Research conducted at the Houghton Lake Wildlife Research Station. 2 Present address: CSIRO, Division of Plant Industry, Private Bag, P. O. Wembley, W. Australia. 732 is prly consumed and digested ( Ullrey et al. lD64). Because of its importance as a forest specaes and its potential use£ulness as a winter deer food, research has been conducted to characterize aspen browse more completely. We acknowledge the counsel olf B. A. Dehority and W. G. Bergen, the laboratory assistance of Hazel Harte, Elizabeth Rimpau, Colleen Patterson, Karen Jones, and Kay Catton, and the assistance in the collection of browse and in animal care provided by E. H. Cunninghamn \2V. G. Hyden F. L. Shippy, and J. R. Terry. EXPERIMENTAL PROCEDURE Three experiments involved 60 bred does over a period o£ 2 years. This content downloaded from 207.46.13.131 on Sun, 16 Oct 2016 05:25:26 UTC All use subject to http://about.jstor.org/terms ASPEN BROWSE FOR DEER * Ullrey et al. 733