The effect of administering multiple doses of tall larkspur (Delphinium barbeyi) to cattle

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

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2015
Publication Date: 8/6/2015
Publication URL: http://handle.nal.usda.gov/10113/62804
Citation: Welch, K.D., Green, B.T., Gardner, D.R., Cook, D., Pfister, J.A. 2015. The effect of administering multiple doses of tall larkspur (Delphinium barbeyi) to cattle. Journal of Animal Science. 93(8):4181-4188.

Interpretive Summary: Larkspurs (Delphinium spp.) are one of the most serious toxic plant problems on foothill and mountain rangelands in the western U.S. A number of valuable management recommendations have been made based upon years of research into larkspur toxicity in livestock. However, in many of these studies cattle were treated with a single bolus dose of finely ground plant material. A single bolus dose of finely ground plant material does not accurately represent the conditions under which animals are poisoned on the range. It has been proposed that cyclic consumption enables cattle to generally regulate larkspur consumption below the second threshold in a typical range setting, which allows most cattle the opportunity to use an otherwise nutritious plant. Consequently, studies need to be conducted using dosing regimens that more realistically mimic the multiple-dose exposures that cattle experience in grazing situations. Therefore, in this study, we performed a dose-response study wherein multiple doses of tall larkspur were administered to cattle at 12 h intervals, with the objective to identify how much tall larkspur cattle can consume daily without serious adverse effects. Additionally, a computer model was generated to simulate multiple-dosing regimens at the various doses and different dosing regimens. The results from this study suggest that a 500 kg cow can consume a daily dose of 1.25 kg of fresh tall larkspur (with a similar alkaloid profile) without becoming severely poisoned (suffering from muscle weakness to the point of recumbency). Additionally, these results indicate that a serum concentration of 355 ng methyllycaconitine / ml may represent a toxic threshold.

Technical Abstract: Larkspurs (Delphinium spp.) are one of the most serious toxic plant problems on foothill and mountain rangelands in the western U.S. A considerable amount of research has been conducted over the years in both field and pen settings. The results of these research efforts have significantly increased our understanding of the poisoning of cattle by larkspur plants. However, most of the pen studies conducted thus far have utilized a dosing regimen of a single bolus dose, which does not accurately mimic the manner by which cattle are poisoned by larkspur while grazing. Consequently, the objective of this study was to evaluate the acute toxicity of tall larkspur (D. barbeyi collected near Manti, UT) when administered in multiple doses, with the intent to identify a No Observable Adverse Effect Level (NOAEL). The adverse effect selected for this study was muscle weakness to the point the cattle could no longer remain ambulatory as would be required in a grazing environment, thus becoming sternally recumbent when exercised. Hereford steers were administered various doses of tall larkspur at 12 h intervals for 4 d or until they showed marked signs of muscle weakness. The results suggest that a dose of 2 mg/kg/d N- (methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids is the NOAEL for a tall larkspur population with a norditerpenoid alkaloid profile containing 4 mg MSAL-type / g plant material and 12 mg non MSAL-type alkaloids / g plant material. Additionally, a computer model was generated to simulate multiple-dosing regimens at the various doses and different dosing regimens. The results from this study suggest that a 500 kg cow can consume a daily dose of 1.25 kg of fresh tall larkspur (with a similar alkaloid profile) without becoming severely poisoned (suffering from muscle weakness to the point of recumbency). Additionally, these results indicate that a serum concentration of 355 ng methyllycaconitine / ml may represent a toxic threshold.