The effect of clipping on the growth and miserotoxin content of Columbia milkvetch

Abstract

The growth and miserotoxin content of Columbia milkvetch (Astragalus miser Dougl. var. serotinus (Gray) Barneby) were examined in clipping trials at 2 rangeland sites in southern British Columbia during 1984 and 1986. Growth was determined by measuring the freeze-dried weight of each plant and miserotoxin levels were estimated by a rapid screening method that simplified sample preparation for spectrophotometric determination. In both years and at both sites, growth and toxicity were substantially reduced in response to early clipping in the spring. In comparison to untreated plants, the aboveground biomass of clipped plants was reduced by at least 50% during a 6-wk period of regrowth. A similar reduction was also observed in the miserotoxin content of clipped plants. The results indicate that early grazing may reduce the potential hazard of timber milkvetch to livestock.