SEASONAL GRAZING OF COLUMBIA MILKVETCH BY CATTLE ON RANGELANDS IN BRITISH-COLUMBIA

There is a dearth of knowledge on the selection and utilization of Col umbia milkvetch (Astragalus miser Dougl. ex Hook. var. serotinus) by g razing livestock on rangelands in British Columbia, Four grazing trial s were conducted with cattle on Columbia milkvetch range in southern i nterior British Columbia, In the first 2 trials during 1990 and 1991 c attle grazed an upper grassland site in late spring, In 1992 and 1993, the animals grazed a lodgepole pine forest site during early summer, The density of Columbia milkvetch and its basal area were similar at b oth locations, The Columbia milkvetch was not a preferred species on t he grassland site as indicated by the bite count technique that determ ined its percentage in the diet, Consumption of Columbia milkvetch inc reased gradually as other forage species were preferentially selected and depleted, On the grasslands, consumption of Columbia milkvetch by individual animals did not show an addictive pattern, At the forest si te, utilization of Columbia milkvetch was determined on a weekly basis during 1992 and on a biweekly basis during 1993 by paired plots, In c ontrast to the grassland site, Columbia milkvetch was a preferred spec ies at the forest site where it was utilized to a greater extent than grasses or other forbs, Approximately 80% of the Columbia milkvetch wa s utilized during 1992 and 60% during 1993, which was significantly gr eater than the utilization of grasses or other forbs, Forage nutrient analysis at the forest site indicated Columbia milkvetch had higher cr ude protein and lower ADF content than other forages but it caused liv estock poisoning in 1993.