Role of secondary chemistry of tarbush in herbivory by livestock

TitleRole of secondary chemistry of tarbush in herbivory by livestock
Publication TypeConference Paper
Year of Publication1992
AuthorsEstell R.E., Fredrickson E.L., Havstad K, Anderson D.M.
Conference NameAnnual Meeting, Society for Range Management
Date Published1992

Tarbush (Flourensia cemua) is an abundant shrub in the Chihuahuan desert which is used to a limited degree by ruminants. Related current research has demonstrated differential livestock use within this species. We hypothesize that grazing ruminants express selection preference for individual tarbush plants based upon leaf surface concentrations of epicuticular waxes and terpenoids. The objective of this study was to examine the leaf surface chemistry of tarbush in relation to degree of use by ruminants. Samples were collected in the mature leaf stage on 2 sites from plants exhibiting either high (>40%) or low (<5%) degree of use when browsed by cattle, sheep, and goats confined to a small area (10 plants per use category per site). Use was estimated visually and approximately 50 g of leaves from each plant were removed and placed on dry ice. Epicuticular waxes were determined with a gravimetric procedure, using a chloroform extraction of whole leaves. Leaves were also extracted in ethanol for mono- and sesquiterpenoid analysis with gas chromotography/mass spectrophotometry. The chloroform extraction revealed a greater concentration of epicuticular wax on the leaf surface of plants which were used to a lower degree (P < 0.02). Epicuticular wax concentration was 9.5 and 12.0% (organic matter basis) for high and low use plants, respectively. Data will be presented on surface terpenoid concentrations and their relationship to degree of use of tarbush by grazing ruminants. Information obtained on surface chemistry might be exploited to enhance use of tarbush as a forage.