Consumption of Low Larkspur (Delphinium nuttallianum) by Grazing Sheep

Abstract

Low larkspur (Delphinium nuttallianum Pritz.) poisoning causes serious economic loss to livestock producers that graze cattle on foothill and mountain ranges in western North America. In general, all Delphinium spp. are five times less toxic to sheep than to cattle. Because low larkspurs are less toxic to sheep than cattle, grazing sheep before cattle on rangelands with dense populations of low larkspur can reduce larkspur density and risk of poisoning to grazing cattle. All previous published work on sheep and larkspur interactions has involved tall larkspurs. This series of studies was conducted to determine if sheep would consume sufficient low larkspur to reduce subsequent risk to cattle. Four summer trials were conducted in Collbran, Colorado, and Soda Springs, Idaho on pastures with dense (> 9 plants m-2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (two sheep 0.015 ha-1 for 9 d), sheep consumed little low larkspur, but animals appeared to trample much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 mg g-1 to 1.6 mg g-1 in all trials. The use of sheep to graze low larkspurs to reduce subsequent consumption by grazing cattle does not appear to be a viable option.