TOXIC ALKALOID LEVELS IN TALL LARKSPUR (DELPHINIUM-BARBEYI) IN WESTERN COLORADO

Consumption of tall larkspur (Delphinium barbeyi L. Huth.) can be fata l to cattle grazing mountain rangeland during summer. Tall larkspur co ntains many alkaloids, but virtually all the toxicity is caused by met hyl succidimido anthranoyl lycoctonine-type (MSAL) diterpenoid alkaloi ds. We measured the concentration of MSAL alkaloids (% of dry matter) in tall larkspur in various phenological stages during 1990, 1991, and 1992 near Yampa, Colorado. The site represented tall larkspur-infeste d rangelands on the western slope of the Rocky Mountains. Toxic alkalo id concentrations were greatest (0.4 to 0.6%) early in the growing sea son (bud stage). Toxic alkaloid concentrations were generally static d uring the flower and pod stages, or increased during the pod stage. Im mature leaves had greater MSAL alkaloid concentrations early in the gr owing season compared to flowering parts. Alkaloid concentrations in p ods were greater than in leaves (P<0.05; pod stage), as pod concentrat ions increased to 0.4% late in the growing season. In 2 of 3 years, pl ant parts did not differ in MSAL alkaloid concentrations, although wea ther conditions differed each year. Concentrations of toxic alkaloids did not seem to influence amounts of tall larkspur consumed by grazing cattle on the same sampling dates. Many livestock producers defer gra zing of tall larkspur ranges until the plant is in the pod stage becau se of a general belief that toxicity is greatly reduced. Our results s uggest that grazing tall larkspur ranges during the pod state may exac erbate cattle losses if MSAL alkaloid concentrations do not decrease, yet consumption by cattle increases.