Grazing of Delphinium occidentale (duncecap larkspur) by susceptible and resistant cattle

Authors: Pfister, James; Green, Benedict - Ben; Gardner, Dale; Welch, Kevin; Cook, Daniel; Stonecipher, Clinton - Clint

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2018
Publication Date: 12/10/2018
Citation: Pfister, J.A., Green, B.T., Gardner, D.R., Welch, K.D., Cook, D., Stonecipher, C.A. 2018. Grazing of Delphinium occidentale (duncecap larkspur) by susceptible and resistant cattle. Professional Animal Scientist. 34(6):581-593. https://doi.org/10.15232/pas.2018-01775.
DOI: https://doi.org/10.15232/pas.2018-01775

Interpretive Summary: Delphinium spp. (larkspurs) often fatally poison grazing cattle. Angus cattle differing in susceptibility (i.e., either susceptible or resistant) to larkspur poisoning were used to assess diet selection of duncecap larkspur (Delphinium occidentale) while grazing. During July 2015, 2016, and 2017, diet selection of 12 cattle (6 susceptible, 6 resistant) was determined for 2 to 3 weeks. During 2015 resistant steers ate 6% of their diets as total larkspur compared to 7% for susceptible steers. During 2016 resistant steers consumed more larkspur on 5 trial days than did susceptible steers. Overall in 2016, resistant steers ate 6% of their diets as larkspur compared to 3% for susceptible steers. During 2017 resistant heifers consumed more larkspur on 2 trial days than did susceptible heifers. Overall, during 2017 resistant heifers ate 7% of their diets as larkspur compared to 3% for susceptible heifers. The average blood concentration of the dominant alkaloid, methyllycaconitine, in severely intoxicated, susceptible animals was approximately 700 ng/mL compared to approximately 1000 ng/mL for severely intoxicated, resistant animals. Two susceptible animals died during the study, whereas no resistant animals died. The diet selection and comparative responses of resistant and susceptible animals on rangeland appears to validate the phenotyping done in the laboratory. Selecting resistant cattle to graze larkspur-infested rangelands may reduce losses, however, further research is required to develop genetic biomarkers to identify such animals.

Technical Abstract: Delphinium spp. (larkspurs) often fatally poison grazing cattle. Angus cattle differing in susceptibility to larkspur poisoning were used to assess selection of larkspur (Delphinium occidentale) while grazing. During July 2015, 2016, and 2017, diet selection of 12 cattle (6 susceptible, 6 resistant) was determined for 2 to 3 weeks. During 2015 resistant steers ate 6% of their diets as total larkspur compared to 7% (P > 0.34) for susceptible steers. During 2016 there was a treatment x day interaction (P = 0.02) for total larkspur consumption as resistant steers consumed more larkspur on 5 trial days than did susceptible steers. Overall, resistant steers ate 6% of their diets as larkspur compared to 3% for susceptible steers. During 2017 there was a treatment x day interaction (P = 0.03) for total larkspur consumption as resistant heifers consumed more larkspur on 2 trial days than did susceptible heifers. Overall, during 2017 resistant heifers ate 7% of their diets as larkspur compared to 3% for susceptible heifers. The average serum concentration of the dominant alkaloid, methyllycaconitine, in severely intoxicated, susceptible animals was approximately 700 ng/mL compared to approximately 1000 ng/mL for severely intoxicated, resistant animals. The only fatalities (2) were in susceptible animals. The diet selection and comparative responses of resistant and susceptible animals on rangeland appears to validate the phenotyping done in the laboratory. Selecting resistant cattle to graze larkspur-infested rangelands may reduce losses, however, further research is required to develop genetic biomarkers to identify such animals.