Consumption of Low Larkspur (Delphinium nuttallianum) by Grazing Sheep

Authors: Pfister, James; Gardner, Dale; Panter, Kip

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2009
Publication Date: 5/1/2010
Citation: Pfister, J.A., Gardner, D.R., Panter, K.E. 2010. Consumption of Low Larkspur (Delphinium nuttallianum) by Grazing Sheep. Rangeland Ecology and Management, 63(2):263-266.

Interpretive Summary: Low larkspur (Delphinium nuttallianum) poisoning causes serious death loss to livestock producers that graze cattle on foothill and mountain ranges. In general, all Delphinium spp. are five times less toxic to sheep than to cattle. Because sheep are less susceptible to larkspur toxicity, ranchers may be able to graze sheep before cattle on rangelands with dense low larkspur populations to reduce larkspur density, and thus reduce later risk to grazing cattle. These studies were conducted to determine if sheep would consume sufficient low larkspur to reduce subsequent risk to cattle. Four summer trials were conducted in Collbran, CO, and Soda Springs, ID on pastures with dense (> 9 plants/m2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (2 sheep/0.015 ha for 9 days), sheep consumed little low larkspur, but animals trampled much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 to 1.6 mg/g 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. Sheep may be used under some circumstances, however, to trample dense low larkspur populations.

Technical 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 sheep are less susceptible to larkspur toxicity, ranchers may be able to graze sheep before cattle on rangelands with dense low larkspur populations to reduce larkspur density, and thus reduce later risk 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, CO, and Soda Springs, ID on pastures with dense (> 9 plants/m2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (2 sheep/0.015 ha for 9 days), sheep consumed little low larkspur, but animals trampled much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 to 1.6 mg/g 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. Sheep may be used, however, to trample dense low larkspur populations.