Effects of Secondary Metabolites from Balsam Poplar and Paper Birch on Cellulose Digestion

Abstract

Inhibitory effects of metabolites from balsam poplar (Pops Unpublished data, P.B. Reichardt) and the relative amounts present in juvenile and mature plants and plant parts are being quantified. In addition, bioassays are being conducted to evaluate deterrent properties of different resin fractions isolated (Bryant and Kuropat 1980, Bryant 1981, Bryant et al. 1983, Unpublished data, P.B. Reichardt). Bryant and Kuropat (1980) speculated that current annual growth (CAG) twigs ofjuvenile Alaska paper birch are less digestible than CAG twigs from mature-growth-form plants due to their higher resin content, which may be toxic to rumen microbes. Previous studies have demonstrated antibacterial effects or inhibition of digestion by rumen microbes exposed to various terpenoids. Nagy et al. (1964) found that essential oils in sagebrush (Artemisia tridentata) inhibited bacterial growth and decreased gas and volatile fatty acid production in rumen of mule deer (Odocoileus hemionus). Oh et al. (1967) and Longhurst et al. (1968) found that oxygenated monoterpenes present in Douglas fir (Psuedotsuga menziesii) needles strongly inhibited Columbian black-tailed deer (0.h.’ columbianus) rumen microbial activity. Schwartz et al. (1980) reported that volatile oils present in various junipers (Juniperus spp.) reduced cellulose digestion in vitro by up to 40%. In this paper, we present evidence that benzyl alcohol, cineok papyrifcric acid, and a steam distillate fraction from juvenile Alaska paper birch depress in vitro fermentation of cellulose SUSpended in rumen fluid from wapiti (Cervus elaphus nelsoni). Material and Methods Four resin components, 2 each from balsam poplar and paper Authorsare research assistant, Department of Biological Sciences, MichiganTechnological University, Houghton 49931; research assistants, Department of Animal Sciences, University of Alberta, Edmonton T6G 2P5. The authors thank the following persons for their support and assistance with various aspects of this study: J. Bryant, P. Reichardt, R. Hudson, L. Jebson, D. Renecker, J. Aalhus, D. Summers, and T. Fenton. Financial support for this study was prowded by Michigan Technological University and the University of Alberta. Manuscript accepted October 15, 1984. 370 birch, were chosen for testing because of their ability to deter browsing by snowshoe hare (Lepus americanus) (Unpublished data, J.P. Bryant). Papyriferic acid, a triterpene carboxylic acid, and a steam distillate fraction, composed primarily of sesquiterpenes, from juvenile Alaska paper birch were provided by Dr. P.B. Reichardt (Department of Chemistry, University of Alaska, Fairbanks). Papyriferic acid was isolated from diethyl ether extract of CAG twigs from winterdormant juvenile plants by column chromatography. The steam distillable fraction of juvenile paper birch was isolated by diethyl ether extraction of the steam distillate (Personal communication, P. Reichardt). In addition, cineole (an isoprenoid) and benzyl alcohol, 2 compounds present in balsam poplar bud resin, were obtained commercially (Sigma Corp., St. Louis, MO.). Sample Preparation Concentrations of resin fractions used for in vitro trials were based on the amount of each resin component available and on the amount estimated to be present in CAG twigs from both mature and juvenile forms of paper birch and balsam poplar (Unpublished data, P.B. Reichardt). Because of the limited availability of papyriferic acid and paper birch steam distillate, treatment concentrations for these compounds were 5 and 20 mg per gram of substrate. Cineole and benzyl alcohol were tested at concentrations of 5, 10, 20,40, and 100 mg per gram of substrate. All treatment concentrations were prepared on a dry weight basis. Commercial purified cellulose (“Alpha floe”, Lee Chemicals Ltd., Toronto, Ont.) was used as a substrate. Resin components were dissolved in excess acetone, placed into a 150-ml round-bottom flask with the cellulose substrate, and swirled until the material was saturated. The flask was then placed on a vacuum rotodistiller with a water bath temperature of 50°C for approximately 10 minutes, or until the acetone had evaporated. The treated cellulose was removed from the flask, placed into metal dishes, and oven-dried at 4O“C for 48 hours. Following drying, samples were mixed in a micro mill and stored in sealed glass containers. In Vitro Techniques The in vitro techniques used to measure digestion of dry matter were developed by Tilley and Terry (1963) and modified by Morgantini and Hudson (in press). Rumen inoculum was obtained from a fistulated wapiti steer which was maintained on pelleted aspen concentrate, alfalfa hay, freshly cut browse, and fresh grass available ad libitum in a l-ha pasture. Triplicate samples were tested at each concentration level. Acetone controls were also tested for antimicrobial effects. Differences were tested by one-way analysis of variance and Duncan’s new multiple range test (KO.05).