Cattle grazing toxic Delphinium andersonii in South-Central Idaho

Authors: Pfister, James; Cook, Daniel; Gardner, Dale

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2011
Publication Date: 11/1/2011
Citation: Pfister, J.A., Cook, D., Gardner, D.R. 2011. Cattle grazing toxic Delphinium andersonii in South-Central Idaho. Rangeland Ecology and Management. 64(6): 664-8.

Interpretive Summary: Anderson larkspur (Delphinium andersonii) is a toxic plant responsible for many cattle deaths on western U.S. rangelands. There is no published information about cattle grazing of Anderson larkspur, thus the objectives of the study were to determine when cattle consumed larkspur in relation to plant growth and toxicity, and to determine if animal age (heifers vs. mature cows) influenced selection of larkspur. These grazing studies were conducted during spring and early summer, 2008 and 2009, on sagebrush rangeland near Picabo, Idaho. Total toxic alkaloid concentrations were relatively high, above or near 0.5%. During 2008 cows began to consume Anderson larkspur when flowers appeared, but the consumption peaked during the late flower and pod stage of growth. Over the entire 2008 trial cows ate 3% of their bites as larkspur. During 2009 heifers ate about twice as much Anderson larkspur as did mature cows (5.1% of bites vs. 2.9%, respectively). Heifers ate more Anderson larkspur on several trial days compared to mature cows. Heifers repeatedly consumed sufficient larkspur that they collapsed into lateral recumbency; however, no animals were fatally intoxicated. Heifers appeared to become transiently averted to larkspur; however, heifers resumed consumption of D. andersonii after a period of one to several days of low or no consumption. Livestock management to reduce losses to Anderson larkspur should include timed grazing to avoid infested pastures during full flower to pod phenological stages, and grazing with older animals rather than yearling heifers.

Technical Abstract: Anderson larkspur (Delphinium andersonii A. Gray) is a toxic plant responsible for cattle death losses on semi-arid rangelands in the western United States. There is no published information about cattle grazing of Anderson larkspur, thus the objectives of the present study were to determine when cattle consumed Anderson larkspur in relation to plant phenology and toxicity, and to determine if animal age influenced selection of Anderson larkspur. These grazing studies were conducted during spring and early summer, 2008 and 2009, on sagebrush rangeland near Picabo, Idaho. Eight, six to seven year old mature Angus cows were used in 2008; whereas during 2009, 12 Angus cattle were used, including six yearling heifers and six, five-year old cows. The overall density of Anderson larkspur was 2.8 plants • m-2 during 2008, and 4.9 plants • m-2 during 2009. Total toxic alkaloid concentrations in Anderson larkspur plants were near or above 5 mg • g-1 during both studies. During 2008 cows began to consume Anderson larkspur when flowers appeared, but the consumption peaked during the late flower and pod stage of growth. Over the entire 2008 trial cows ate 3% of their bites as larkspur. During 2009 heifers ate about twice as much Anderson larkspur as did mature cows (5.1% of bites vs. 2.9%, respectively). Heifers ate more (P < 0.05) Anderson larkspur on several trial days compared to mature cows. Heifers repeatedly consumed sufficient larkspur that they collapsed into lateral recumbency; however, no animals were fatally intoxicated. Heifers appeared to become transiently averted to larkspur; however, heifers resumed consumption of D. andersonii after a period of one to several days of low or no consumption. Livestock management to reduce losses to Anderson larkspur should include timed grazing to avoid infested pastures during full flower to pod phenological stages, and grazing with older animals rather than yearling heifers.