Dynamics of larkspur (Delphinium barbeyi) pellet consumption and tolerance of the inhibitory effects of larkspur alkaloids on muscle function in cattle

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

Submitted to: Poisonous Plant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2020
Publication Date: 4/16/2020
Citation: Green, B.T., Pfister, J.A., Gardner, D.R., Welch, K.D., Cook, D. 2020. Dynamics of larkspur (Delphinium barbeyi) pellet consumption and tolerance of the inhibitory effects of larkspur alkaloids on muscle function in cattle. Poisonous Plant Research. 3:28-41. https://doi.org/10.26077/zsrd-d783.
DOI: https://doi.org/10.26077/zsrd-d783

Interpretive Summary: Larkspurs (Delphinium spp.) are native plants on foothill and mountain rangelands in western North America that poison cattle. The severity of the poisoning depends on the genetic background of the cattle, the amount of plant consumed, the rate of consumption, and the concentrations of toxic norditerpene alkaloids in the plants. Identifying cattle which are naturally resistant to larkspur intoxication would improve grazing animal welfare on these rangelands and reduce losses to poisonous plants.

Technical Abstract: Larkspurs (Delphinium spp.) are toxic native plants on foothill and mountain rangelands in western North America. The purpose of this study was to examine in a laboratory setting, the subclinical effects of larkspur intake and toxicosis, by allowing larkspur susceptible and resistant cattle to self-select the amount of larkspur consumed in pellet form. We hypothesized that there would be differences in chronic pellet consumption patterns between susceptible and resistant animals. Two trials were completed, each with 6 larkspur resistant and 6 larkspur susceptible Angus steers. Trial 1 consisted of a 12% larkspur-alfalfa pellet. Trial 2 consisted of a 6% larkspur-alfalfa pellet with 5% molasses to improve palatability. A blood sample was obtained daily during the trials for serum alkaloid analysis and the steers were exercised on day nine during trial 2 to elicit clinical signs of intoxication. There were no differences in larkspur consumption between the groups during either trial. The cattle were quickly averted to the 12% larkspur pellet in trial 1. During trial 2, the resistant steers consumed 6% more larkspur pellets compared to susceptible steers. The susceptible and resistant steers differed in serum concentrations of methyllycaconitine (MLA) on days 9 to 12 (P < 0.01) but did not have significantly different exercise times (38.0 ± 3 min and 27.2 ± 6.5 min for resistant and susceptible steers, respectively, t-test P = 0.11). These results suggest the development of pharmacodynamic tolerance to larkspur alkaloids by the steers through the upregulation of cellular responses and an increase in receptor numbers due to a prolonged blockade of nicotinic acetylcholine receptor function. Further work will be required to determine whether there are differences between susceptible and resistant animals in toxicokinetic responses such as serum absorption and elimination.